[v8,4/5] gdb: introduce ability to disable frame unwinders

  Sometimes, in the GDB testsuite, we want to test the ability of specific
unwinders to handle some piece of code. Usually this is done by trying
to outsmart GDB, or by coercing the compiler to remove information that
GDB would rely on.  Both approaches have problems as GDB gets smarter
with time, and that compilers might differ in version and behavior, or
simply introduce new useful information. This was requested back in 2003
in PR backtrace/8434.

To improve our ability to thoroughly test GDB, this patch introduces a
new maintenance command that allows a user to disable some unwinders,
based on either the name of the unwinder or on its class. With this
change, it will now be possible for GDB to not find any frame unwinders
for a given frame, which would previously cause GDB to assert. GDB will
now check if any frame unwinder has been disabled, and if some has, it
will just error out instead of asserting.

Unwinders can be disabled or re-enabled in 3 different ways:
* Disabling/enabling all at once (using '-all').
* By specifying an unwinder class to be disabled (option '-class').
* By specifying the name of an unwinder (option '-name').

If you give no options to the command, GDB assumes the input is an
unwinder class. '-class' would make no difference if used, is just here
for completeness.

This command is meant to be used once the inferior is already at the
desired location for the test. An example session would be:

(gdb) start
Temporary breakpoint 1, main () at omp.c:17
17          func();
(gdb) maint frame-unwinder disable ARCH
(gdb) bt
\#0  main () at omp.c:17
(gdb) maint frame-unwinder enable ARCH
(gdb) cont
Continuing.

This commit is a more generic version of commit 3c3bb0580be0,
and so, based on the final paragraph of the commit message:
    gdb: Add switch to disable DWARF stack unwinders
<...>
    If in the future we find ourselves adding more switches to disable
    different unwinders, then we should probably move to a more generic
    solution, and remove this patch.
this patch also reverts 3c3bb0580be0

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=8434
Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
---
 gdb/NEWS                                      |  17 ++
 gdb/doc/gdb.texinfo                           |  49 ++--
 gdb/dwarf2/frame-tailcall.c                   |   3 -
 gdb/dwarf2/frame.c                            |  30 ---
 gdb/dwarf2/frame.h                            |   6 -
 gdb/frame-unwind.c                            | 237 +++++++++++++++++-
 gdb/frame-unwind.h                            |   9 +
 .../gdb.base/frame-info-consistent.exp        |   8 +-
 gdb/testsuite/gdb.base/frame-unwind-disable.c |  22 ++
 .../gdb.base/frame-unwind-disable.exp         | 137 ++++++++++
 gdb/testsuite/gdb.base/maint.exp              |   4 -
 11 files changed, 437 insertions(+), 85 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.c
 create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.exp
  

Guinevere Larsen <guinevere@redhat.com> writes:

> Sometimes, in the GDB testsuite, we want to test the ability of specific
> unwinders to handle some piece of code. Usually this is done by trying
> to outsmart GDB, or by coercing the compiler to remove information that
> GDB would rely on.  Both approaches have problems as GDB gets smarter
> with time, and that compilers might differ in version and behavior, or
> simply introduce new useful information. This was requested back in 2003
> in PR backtrace/8434.
>
> To improve our ability to thoroughly test GDB, this patch introduces a
> new maintenance command that allows a user to disable some unwinders,
> based on either the name of the unwinder or on its class. With this
> change, it will now be possible for GDB to not find any frame unwinders
> for a given frame, which would previously cause GDB to assert. GDB will
> now check if any frame unwinder has been disabled, and if some has, it
> will just error out instead of asserting.
>
> Unwinders can be disabled or re-enabled in 3 different ways:
> * Disabling/enabling all at once (using '-all').
> * By specifying an unwinder class to be disabled (option '-class').
> * By specifying the name of an unwinder (option '-name').
>
> If you give no options to the command, GDB assumes the input is an
> unwinder class. '-class' would make no difference if used, is just here
> for completeness.
>
> This command is meant to be used once the inferior is already at the
> desired location for the test. An example session would be:
>
> (gdb) start
> Temporary breakpoint 1, main () at omp.c:17
> 17          func();
> (gdb) maint frame-unwinder disable ARCH
> (gdb) bt
> \#0  main () at omp.c:17
> (gdb) maint frame-unwinder enable ARCH
> (gdb) cont
> Continuing.
>
> This commit is a more generic version of commit 3c3bb0580be0,
> and so, based on the final paragraph of the commit message:
>     gdb: Add switch to disable DWARF stack unwinders
> <...>
>     If in the future we find ourselves adding more switches to disable
>     different unwinders, then we should probably move to a more generic
>     solution, and remove this patch.
> this patch also reverts 3c3bb0580be0
>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=8434
> Reviewed-By: Eli Zaretskii <eliz@gnu.org>
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
> ---
>  gdb/NEWS                                      |  17 ++
>  gdb/doc/gdb.texinfo                           |  49 ++--
>  gdb/dwarf2/frame-tailcall.c                   |   3 -
>  gdb/dwarf2/frame.c                            |  30 ---
>  gdb/dwarf2/frame.h                            |   6 -
>  gdb/frame-unwind.c                            | 237 +++++++++++++++++-
>  gdb/frame-unwind.h                            |   9 +
>  .../gdb.base/frame-info-consistent.exp        |   8 +-
>  gdb/testsuite/gdb.base/frame-unwind-disable.c |  22 ++
>  .../gdb.base/frame-unwind-disable.exp         | 137 ++++++++++
>  gdb/testsuite/gdb.base/maint.exp              |   4 -
>  11 files changed, 437 insertions(+), 85 deletions(-)
>  create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.c
>  create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.exp
>
> diff --git a/gdb/NEWS b/gdb/NEWS
> index 245b355669a..ef3317c11cb 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -125,6 +125,13 @@ maintenance info blocks [ADDRESS]
>    are listed starting at the inner global block out to the most inner
>    block.
>  
> +maintenance frame-unwinder disable [-all | -name NAME | [-class] CLASS]
> +maintenance frame-unwinder enable [-all | -name NAME | [-class] CLASS]
> +  Enable or disable frame unwinders.  This is only meant to be used when
> +  testing unwinders themselves, and you want to ensure that a fallback
> +  algorithm won't obscure a regression.  GDB is not expected to behave
> +  well if you try to execute the inferior with unwinders disabled.
> +
>  info missing-objfile-handlers
>    List all the registered missing-objfile handlers.
>  
> @@ -167,6 +174,16 @@ maintenance print remote-registers
>  mainenance info frame-unwinders
>    Add a CLASS column to the output.  This class is a somewhat arbitrary
>    grouping of unwinders, based on which area of GDB adds the unwinder.
> +  Also add an ENABLED column, that will show if the unwinder is enabled
> +  or not.
> +
> +maintenance set dwarf unwinders (on|off)
> +  This command has been removed because the same functionality can be
> +  achieved with maint frame-unwinder (enable|disable) DEBUGINFO.
> +
> +maintenance show dwarf unwinders
> +  This command has been removed since the functionality can be achieved
> +  by checking the last column of maint info frame-unwinders.
>  
>  show configuration
>    Now includes the version of GNU Readline library that GDB is using.
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index 115c1f46b7f..10e6654a03b 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -42210,31 +42210,6 @@ On hosts without threading, or where worker threads have been disabled
>  at runtime, this setting has no effect, as DWARF reading is always
>  done on the main thread, and is therefore always synchronous.
>  
> -@kindex maint set dwarf unwinders
> -@kindex maint show dwarf unwinders
> -@item maint set dwarf unwinders
> -@itemx maint show dwarf unwinders
> -Control use of the DWARF frame unwinders.
> -
> -@cindex DWARF frame unwinders
> -Many targets that support DWARF debugging use @value{GDBN}'s DWARF
> -frame unwinders to build the backtrace.  Many of these targets will
> -also have a second mechanism for building the backtrace for use in
> -cases where DWARF information is not available, this second mechanism
> -is often an analysis of a function's prologue.
> -
> -In order to extend testing coverage of the second level stack
> -unwinding mechanisms it is helpful to be able to disable the DWARF
> -stack unwinders, this can be done with this switch.
> -
> -In normal use of @value{GDBN} disabling the DWARF unwinders is not
> -advisable, there are cases that are better handled through DWARF than
> -prologue analysis, and the debug experience is likely to be better
> -with the DWARF frame unwinders enabled.
> -
> -If DWARF frame unwinders are not supported for a particular target
> -architecture, then enabling this flag does not cause them to be used.
> -
>  @kindex maint info frame-unwinders
>  @item maint info frame-unwinders
>  List the frame unwinders currently in effect, starting with the highest
> @@ -42252,6 +42227,30 @@ Unwinders installed by debug information readers.
>  Unwinders installed by the architecture specific code.
>  @end table
>  
> +@kindex maint frame-unwinder disable
> +@kindex maint frame-unwinder enable
> +@item maint frame-unwinder disable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
> +@item maint frame-unwinder enable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
> +Disable or enable frame unwinders.  This is meant only as a testing tool, and
> +@value{GDBN} is not guaranteed to work properly if it is unable to find
> +valid frame unwinders.
> +
> +The meaning of each of the invocations are as follows:
> +
> +@table @samp
> +@item @code{-all}
> +Disable or enable all unwinders.
> +@item @code{-name} @var{name}
> +@var{name} is the exact name of the unwinder to be disabled or enabled.
> +@item [@code{-class}] @var{class}
> +@var{class} is the class of frame unwinders to be disabled or enabled.
> +The class may include the prefix @code{FRAME_UNWINDER_}, but it is not
> +required.
> +@end table
> +
> +@var{name} and @var{class} are always case insensitive.  If no option
> +starting wth @code{-} is given, @value{GDBN} assumes @code{-class}.
> +
>  @kindex maint set worker-threads
>  @kindex maint show worker-threads
>  @item maint set worker-threads
> diff --git a/gdb/dwarf2/frame-tailcall.c b/gdb/dwarf2/frame-tailcall.c
> index 54813d00b03..2d7ab740f62 100644
> --- a/gdb/dwarf2/frame-tailcall.c
> +++ b/gdb/dwarf2/frame-tailcall.c
> @@ -321,9 +321,6 @@ tailcall_frame_sniffer (const struct frame_unwind *self,
>    int next_levels;
>    struct tailcall_cache *cache;
>  
> -  if (!dwarf2_frame_unwinders_enabled_p)
> -    return 0;
> -
>    /* Inner tail call element does not make sense for a sentinel frame.  */
>    next_frame = get_next_frame (this_frame);
>    if (next_frame == NULL)
> diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
> index 85e1d59bc09..e0e8eb5dbec 100644
> --- a/gdb/dwarf2/frame.c
> +++ b/gdb/dwarf2/frame.c
> @@ -183,9 +183,6 @@ static ULONGEST read_encoded_value (struct comp_unit *unit, gdb_byte encoding,
>  				    unrelocated_addr func_base);
>  
>  
> -/* See dwarf2/frame.h.  */
> -bool dwarf2_frame_unwinders_enabled_p = true;
> -
>  /* Store the length the expression for the CFA in the `cfa_reg' field,
>     which is unused in that case.  */
>  #define cfa_exp_len cfa_reg
> @@ -1306,9 +1303,6 @@ static int
>  dwarf2_frame_sniffer (const struct frame_unwind *self,
>  		      const frame_info_ptr &this_frame, void **this_cache)
>  {
> -  if (!dwarf2_frame_unwinders_enabled_p)
> -    return 0;
> -
>    /* Grab an address that is guaranteed to reside somewhere within the
>       function.  get_frame_pc(), with a no-return next function, can
>       end up returning something past the end of this function's body.
> @@ -2253,34 +2247,10 @@ dwarf2_build_frame_info (struct objfile *objfile)
>    set_comp_unit (objfile, unit.release ());
>  }
>  
> -/* Handle 'maintenance show dwarf unwinders'.  */
> -
> -static void
> -show_dwarf_unwinders_enabled_p (struct ui_file *file, int from_tty,
> -				struct cmd_list_element *c,
> -				const char *value)
> -{
> -  gdb_printf (file,
> -	      _("The DWARF stack unwinders are currently %s.\n"),
> -	      value);
> -}
> -
>  void _initialize_dwarf2_frame ();
>  void
>  _initialize_dwarf2_frame ()
>  {
> -  add_setshow_boolean_cmd ("unwinders", class_obscure,
> -			   &dwarf2_frame_unwinders_enabled_p , _("\
> -Set whether the DWARF stack frame unwinders are used."), _("\
> -Show whether the DWARF stack frame unwinders are used."), _("\
> -When enabled the DWARF stack frame unwinders can be used for architectures\n\
> -that support the DWARF unwinders.  Enabling the DWARF unwinders for an\n\
> -architecture that doesn't support them will have no effect."),
> -			   NULL,
> -			   show_dwarf_unwinders_enabled_p,
> -			   &set_dwarf_cmdlist,
> -			   &show_dwarf_cmdlist);
> -
>  #if GDB_SELF_TEST
>    selftests::register_test_foreach_arch ("execute_cfa_program",
>  					 selftests::execute_cfa_program_test);
> diff --git a/gdb/dwarf2/frame.h b/gdb/dwarf2/frame.h
> index 2167310fbdf..fe2d669a983 100644
> --- a/gdb/dwarf2/frame.h
> +++ b/gdb/dwarf2/frame.h
> @@ -198,12 +198,6 @@ struct dwarf2_frame_state
>    bool armcc_cfa_offsets_reversed = false;
>  };
>  
> -/* When this is true the DWARF frame unwinders can be used if they are
> -   registered with the gdbarch.  Not all architectures can or do use the
> -   DWARF unwinders.  Setting this to true on a target that does not
> -   otherwise support the DWARF unwinders has no effect.  */
> -extern bool dwarf2_frame_unwinders_enabled_p;
> -
>  /* Set the architecture-specific register state initialization
>     function for GDBARCH to INIT_REG.  */
>  
> diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
> index 3ab6af1c4da..968bb846402 100644
> --- a/gdb/frame-unwind.c
> +++ b/gdb/frame-unwind.c
> @@ -29,6 +29,7 @@
>  #include "gdbarch.h"
>  #include "dwarf2/frame-tailcall.h"
>  #include "cli/cli-cmds.h"
> +#include "cli/cli-option.h"
>  #include "inferior.h"
>  
>  /* Conversion list between the enum for frame_unwind_class and
> @@ -89,6 +90,20 @@ frame_unwinder_class_str (frame_unwind_class uclass)
>    return unwind_class_conversion[uclass];
>  }
>  
> +/* Case insensitive search for a frame_unwind_class based on the given
> +   string.  */
> +static enum frame_unwind_class
> +str_to_frame_unwind_class (const char *class_str)
> +{
> +  for (int i = 0; i < UNWIND_CLASS_NUMBER; i++)
> +    {
> +      if (strcasecmp (unwind_class_conversion[i], class_str) == 0)
> +	return (frame_unwind_class) i;
> +    }
> +
> +  error (_("Unknown frame unwind class: %s"), class_str);
> +}
> +
>  void
>  frame_unwind_prepend_unwinder (struct gdbarch *gdbarch,
>  				const struct frame_unwind *unwinder)
> @@ -175,27 +190,46 @@ frame_unwind_find_by_frame (const frame_info_ptr &this_frame, void **this_cache)
>    FRAME_SCOPED_DEBUG_ENTER_EXIT;
>    frame_debug_printf ("this_frame=%d", frame_relative_level (this_frame));
>  
> -  const struct frame_unwind *unwinder_from_target;
> +  /* If we see a disabled unwinder, we assume some test is being run on
> +     GDB, and we don't want to internal_error at the end of this function.  */
> +  bool seen_disabled_unwinder = false;
> +  /* Lambda to factor out the logic of checking if an unwinder is enabled,
> +     testing it and otherwise recording if we saw a disable unwinder.  */
> +  auto test_unwinder = [&] (const struct frame_unwind *unwinder)
> +    {
> +      if (unwinder == nullptr)
> +	return false;
> +
> +      if (!unwinder->enabled ())
> +	{
> +	  seen_disabled_unwinder = true;
> +	  return false;
> +	}
> +
> +      return frame_unwind_try_unwinder (this_frame,
> +					this_cache,
> +					unwinder);
> +    };
>  
> -  unwinder_from_target = target_get_unwinder ();
> -  if (unwinder_from_target != NULL
> -      && frame_unwind_try_unwinder (this_frame, this_cache,
> -				   unwinder_from_target))
> +  if (test_unwinder (target_get_unwinder ()))
>      return;
>  
> -  unwinder_from_target = target_get_tailcall_unwinder ();
> -  if (unwinder_from_target != NULL
> -      && frame_unwind_try_unwinder (this_frame, this_cache,
> -				   unwinder_from_target))
> +  if (test_unwinder (target_get_tailcall_unwinder ()))
>      return;
>  
>    struct gdbarch *gdbarch = get_frame_arch (this_frame);
>    std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>    for (auto unwinder : *table)
> -    if (frame_unwind_try_unwinder (this_frame, this_cache, unwinder))
> -      return;
> +    {
> +      if (test_unwinder (unwinder))
> +	return;
> +    }
>  
> -  internal_error (_("frame_unwind_find_by_frame failed"));
> +  if (seen_disabled_unwinder)
> +    error (_("Required frame unwinder may have been disabled"
> +	     ", see 'maint info frame-unwinders'"));
> +  else
> +    internal_error (_("frame_unwind_find_by_frame failed"));
>  }
>  
>  /* A default frame sniffer which always accepts the frame.  Used by
> @@ -394,10 +428,11 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>    std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>  
>    ui_out *uiout = current_uiout;
> -  ui_out_emit_table table_emitter (uiout, 3, -1, "FrameUnwinders");
> +  ui_out_emit_table table_emitter (uiout, 4, -1, "FrameUnwinders");
>    uiout->table_header (27, ui_left, "name", "Name");
>    uiout->table_header (25, ui_left, "type", "Type");
>    uiout->table_header (9, ui_left, "class", "Class");
> +  uiout->table_header (8, ui_left, "enabled", "Enabled");
>    uiout->table_body ();
>  
>    for (auto unwinder : *table)
> @@ -407,10 +442,145 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>        uiout->field_string ("type", frame_type_str (unwinder->type ()));
>        uiout->field_string ("class", frame_unwinder_class_str (
>  					unwinder->unwinder_class ()));
> +      uiout->field_string ("enabled", unwinder->enabled () ? "Y" : "N");
>        uiout->text ("\n");
>      }
>  }
>  
> +/* Options for disabling frame unwinders.  */
> +struct maint_frame_unwind_options
> +{
> +  std::string unwinder_name;
> +  const char *unwinder_class = nullptr;
> +  bool all = false;
> +};
> +
> +static const gdb::option::option_def maint_frame_unwind_opt_defs[] = {
> +
> +  gdb::option::flag_option_def<maint_frame_unwind_options> {
> +    "all",
> +    [] (maint_frame_unwind_options *opt) { return &opt->all; },
> +    nullptr,
> +    N_("Change the state of all unwinders")
> +  },
> +  gdb::option::string_option_def<maint_frame_unwind_options> {
> +    "name",
> +    [] (maint_frame_unwind_options *opt) { return &opt->unwinder_name; },
> +    nullptr,
> +    N_("The name of the unwinder to have its state changed")
> +  },
> +  gdb::option::enum_option_def<maint_frame_unwind_options> {
> +    "class",
> +    unwind_class_conversion,
> +    [] (maint_frame_unwind_options *opt) { return &opt->unwinder_class; },
> +    nullptr,
> +    N_("The class of unwinders to have their states changed")
> +  }
> +};
> +
> +static inline gdb::option::option_def_group
> +make_frame_unwind_enable_disable_options (maint_frame_unwind_options *opts)
> +{
> +  return {{maint_frame_unwind_opt_defs}, opts};
> +}
> +
> +/* Helper function to both enable and disable frame unwinders.
> +   If ENABLE is true, this call will be enabling unwinders,
> +   otherwise the unwinders will be disabled.  */
> +static void
> +enable_disable_frame_unwinders (const char *args, int from_tty, bool enable)
> +{
> +  if (args == nullptr)
> +    {
> +      if (enable)
> +	error (_("Specify which frame unwinder(s) should be enabled"));
> +      else
> +	error (_("Specify which frame unwinder(s) should be disabled"));
> +    }
> +
> +  struct gdbarch* gdbarch = current_inferior ()->arch ();
> +  std::vector<const frame_unwind *> *unwinder_list
> +    = get_frame_unwind_table (gdbarch);
> +
> +  maint_frame_unwind_options opts;
> +  gdb::option::process_options
> +    (&args, gdb::option::PROCESS_OPTIONS_UNKNOWN_IS_ERROR,
> +     make_frame_unwind_enable_disable_options (&opts));
> +
> +  if ((opts.all && !opts.unwinder_name.empty ())
> +      || (opts.all && opts.unwinder_class != nullptr)
> +      || (!opts.unwinder_name.empty () && opts.unwinder_class != nullptr))
> +    error (_("Options are mutually exclusive"));
> +
> +  /* First see if the user wants to change all unwinders.  */
> +  if (opts.all)
> +    {
> +      for (const frame_unwind *u : *unwinder_list)
> +	u->set_enabled (enable);
> +
> +      reinit_frame_cache ();
> +      return;
> +    }
> +
> +  /* If user entered a specific unwinder name, handle it here.  If the
> +     unwinder is already at the expected state, error out.  */
> +  if (!opts.unwinder_name.empty ())
> +    {
> +      bool did_something = false;
> +      for (const frame_unwind *unwinder : *unwinder_list)
> +	{
> +	  if (strcasecmp (unwinder->name (),
> +			  opts.unwinder_name.c_str ()) == 0)
> +	    {
> +	      if (unwinder->enabled () == enable)
> +		{
> +		  if (unwinder->enabled ())
> +		    error (_("unwinder %s is already enabled"),
> +			     unwinder->name ());
> +		  else
> +		    error (_("unwinder %s is already disabled"),
> +			     unwinder->name ());
> +		}
> +	      unwinder->set_enabled (enable);
> +
> +	      did_something = true;
> +	      break;
> +	    }
> +	}
> +      if (!did_something)
> +	error (_("couldn't find unwinder named %s"),
> +	       opts.unwinder_name.c_str ());
> +    }
> +  else
> +    {
> +      if (opts.unwinder_class == nullptr)
> +	opts.unwinder_class = args;
> +      enum frame_unwind_class dclass = str_to_frame_unwind_class
> +	(opts.unwinder_class);
> +      for (auto unwinder: *unwinder_list)

I think you should stick with the form you use earlier:

  (const frame_unwind *unwinder : *unwinder_list)

But if you really want to stick with auto, then I think:

 (const auto &unwinder : *unwinder_list)

would be OK.


> +	{
> +	  if (unwinder->unwinder_class () == dclass)
> +	    unwinder->set_enabled (enable);
> +	}
> +    }
> +
> +  reinit_frame_cache ();
> +}
> +
> +/* Implement "maint frame-unwinder disable" command.  */
> +static void
> +maintenance_disable_frame_unwinders (const char *args, int from_tty)
> +{
> +  enable_disable_frame_unwinders (args, from_tty, false);
> +}
> +
> +/* Implement "maint frame-unwinder enable" command.  */
> +static void
> +maintenance_enable_frame_unwinders (const char *args, int from_tty)
> +{
> +  enable_disable_frame_unwinders (args, from_tty, true);
> +}
> +
>  void _initialize_frame_unwind ();
>  void
>  _initialize_frame_unwind ()
> @@ -423,4 +593,45 @@ _initialize_frame_unwind ()
>  List the frame unwinders currently in effect.\n\
>  Unwinders are listed starting with the highest priority."),
>  	   &maintenanceinfolist);
> +
> +  /* Add "maint frame-unwinder disable/enable".  */
> +  static struct cmd_list_element *maint_frame_unwinder;
> +
> +  add_basic_prefix_cmd ("frame-unwinder", class_maintenance,
> +			_("Commands handling frame unwinders."),
> +			&maint_frame_unwinder, 0, &maintenancelist);
> +
> +  add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
> +	   _("\
> +Disable one or more frame unwinder(s).\n\
> +Usage: maint frame-unwinder disable [-all | -name NAME | [-class] CLASS]\n\
> +\n\
> +These are the meanings of the options:\n\
> +\t-all    - All available unwinders will be disabled\n\
> +\t-name   - NAME is the exact name of the frame unwinder to be disabled\n\
> +\t-class  - CLASS is the class of unwinders to be disabled. Valid classes are:\n\
> +\t\tGDB       - Unwinders added by GDB core;\n\
> +\t\tEXTENSION - Unwinders added by extension languages;\n\
> +\t\tDEBUGINFO - Unwinders that handle debug information;\n\
> +\t\tARCH      - Unwinders that use architecture-specific information;\n\
> +\n\
> +UNWINDER and NAME are case insensitive."),
> +	   &maint_frame_unwinder);
> +
> +  add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
> +	   _("\
> +Enable one or more frame unwinder(s).\n\
> +Usage: maint frame-unwinder enable [-all | -name NAME | [-class] CLASS]\n\
> +\n\
> +These are the meanings of the options:\n\
> +\t-all    - All available unwinders will be enabled\n\
> +\t-name   - NAME is the exact name of the frame unwinder to be enabled\n\
> +\t-class  - CLASS is the class of unwinders to be enabled. Valid classes are:\n\
> +\t\tGDB       - Unwinders added by GDB core;\n\
> +\t\tEXTENSION - Unwinders added by extension languages;\n\
> +\t\tDEBUGINFO - Unwinders that handle debug information;\n\
> +\t\tARCH      - Unwinders that use architecture-specific information;\n\
> +\n\
> +UNWINDER and NAME are case insensitive."),
> +	   &maint_frame_unwinder);
>  }

At the bottom of this email you'll find a small patch which applies on
top of this and adds some basic command completion.  It doesn't complete
the NAMEs, I'm not sure if there's a good way to do that (yet).  It also
doesn't switch the help text to use the %OPTIONS% mechanism, I tried
that, but I think there may be some bugs with the formatting (I'll look
into it), so I've left that off.

You don't have to, we can add completion later, but I do think it would
be good to merge the patch below with this one.  But it is up to you.
Take a look and see what you think.

> diff --git a/gdb/frame-unwind.h b/gdb/frame-unwind.h
> index 13f18618d24..adf8b47982c 100644
> --- a/gdb/frame-unwind.h
> +++ b/gdb/frame-unwind.h
> @@ -192,6 +192,12 @@ class frame_unwind
>    const frame_data *unwind_data () const
>    { return m_unwind_data; }
>  
> +  bool enabled () const
> +  { return m_enabled; }
> +
> +  void set_enabled (bool state) const
> +  { m_enabled = state; }
> +
>    /* Default stop_reason implementation.  It reports NO_REASON, unless the
>       frame is the outermost.  */
>  
> @@ -245,6 +251,9 @@ class frame_unwind
>    frame_unwind_class m_unwinder_class;
>  
>    const frame_data *m_unwind_data;
> +
> +  /* Whether this unwinder can be used when sniffing.  */
> +  mutable bool m_enabled = true;
>  };
>  
>  /* This is a legacy version of the frame unwinder.  The original struct
> diff --git a/gdb/testsuite/gdb.base/frame-info-consistent.exp b/gdb/testsuite/gdb.base/frame-info-consistent.exp
> index fe0cfad95bc..4f483111a91 100644
> --- a/gdb/testsuite/gdb.base/frame-info-consistent.exp
> +++ b/gdb/testsuite/gdb.base/frame-info-consistent.exp
> @@ -95,11 +95,11 @@ proc compare_frames {frames} {
>      }
>  }
>  
> -proc test {dwarf_unwinder} {
> +proc test {enable} {
>  
>      clean_restart $::binfile
>  
> -    gdb_test_no_output "maint set dwarf unwinder $dwarf_unwinder"
> +    gdb_test_no_output "maint frame-unwinder $enable DEBUGINFO"
>  
>      if {![runto_main]} {
>  	return 0
> @@ -134,6 +134,6 @@ proc test {dwarf_unwinder} {
>      }
>  }
>  
> -foreach_with_prefix dwarf {"off" "on"} {
> -    test $dwarf
> +foreach_with_prefix action {"disable" "enable"} {
> +    test $action
>  }
> diff --git a/gdb/testsuite/gdb.base/frame-unwind-disable.c b/gdb/testsuite/gdb.base/frame-unwind-disable.c
> new file mode 100644
> index 00000000000..bbcfb01316e
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/frame-unwind-disable.c
> @@ -0,0 +1,22 @@
> +/* This testcase is part of GDB, the GNU debugger.
> +
> +   Copyright 2024 Free Software Foundation, Inc.

Remember to update the copyright date when rebasing.

> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +int
> +main ()
> +{
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.base/frame-unwind-disable.exp b/gdb/testsuite/gdb.base/frame-unwind-disable.exp
> new file mode 100644
> index 00000000000..f4cad9a47fd
> --- /dev/null
> +++ b/gdb/testsuite/gdb.base/frame-unwind-disable.exp
> @@ -0,0 +1,137 @@
> +# Copyright 2024 Free Software Foundation, Inc.

And again with the date.

> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +# Test multiple situations in which we may use the maintenance command to
> +# disable and enable frame unwinders, and check that they really are
> +# disabled when they say the are.
> +
> +standard_testfile .c

You can drop '.c' here, it's the default.

> +
> +# Proc to check if the unwinder of the given name is in the desired state.
> +# STATE can be either Y or N.
> +proc check_unwinder_state { unwinder_name state {testname ""} } {
> +    set should_pass false
> +    set command "maint info frame-unwinders"
> +    if {${testname} == ""} {
> +	set testname "checking state ${state} for ${unwinder_name}"
> +    }
> +    gdb_test_multiple "${command}" "${testname}" -lbl {
> +	-re "${unwinder_name}\\s+\\w+\\s+\\w+\\s+${state}\\s+(?=\r\n)" {
> +	    set should_pass true
> +	    exp_continue
> +	}
> +	-re "${command}" {
> +	    exp_continue
> +	}
> +	-re "\\w+\\s+\\w+\\s+\\w+\\s+\\w+\\s+(?=\r\n)" {
> +	    exp_continue
> +	}
> +	-re -wrap "" {
> +	    gdb_assert ${should_pass} "${gdb_test_name}"

I don't think the quotes around "${gdb_test_name}" are needed here?  In
fact, there seem to be a few places where you place quotes around
expansion of a single variable (e.g. "${command}" on the
gdb_test_multiple line), I don't think any of these are needed.

With these changes (and with or without the completion patch):

Approved-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew

> +	}
> +    }
> +}
> +
> +# Check if all unwinders of class UNWINDER_CLASS are in the state STATE.
> +# STATE can be either Y or N.
> +# UNWINDER_CLASS can be one of: GDB, ARCH, EXTENSION, DEBUGINFO.  It can
> +# also be \\w+ if checking all unwinders.
> +proc check_unwinder_class { unwinder_class state {testname ""} } {
> +    set command "maint info frame-unwinders"
> +    set should_pass true
> +    if {$testname == ""} {
> +	set testname "checking if ${unwinder_class} state is ${state}"
> +    }
> +    gdb_test_multiple "${command}" "${testname}" -lbl {
> +	-re "^\[^\r\n\]+\\s+\\w+\\s+${unwinder_class}\\s+\(\[YN\]\)\\s+(?=\r\n)" {
> +	    # The unwinder name may have multiple words, so we need to use the
> +	    # more generic [^\r\n] pattern to match the unwinders.
> +	    set cur_state $expect_out(1,string)
> +	    if {$cur_state == $state} {
> +		set should_pass false
> +	    }
> +	    exp_continue
> +	}
> +	-re "${command}" {
> +	    exp_continue
> +	}
> +	-re -wrap "" {
> +	    gdb_assert ${should_pass} "${gdb_test_name}"
> +	}
> +    }
> +}
> +
> +if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
> +    return -1
> +}
> +
> +if {![runto_main]} {
> +    untested "couldn't run to main"
> +    return
> +}
> +
> +# Test disabling all unwinders.
> +check_unwinder_class "\\w+" "Y" \
> +    "all unwinders enabled before any changes"
> +gdb_test_no_output "maint frame-unwinder disable -all"
> +check_unwinder_class "\\w+" "N" \
> +    "all unwinders were properly disabled"
> +
> +# Test if GDB can still make a backtrace once all unwinders are disabled.
> +# It should be impossible.
> +gdb_test "backtrace" \
> +    ".*Required frame unwinder may have been disabled, see 'maint info frame-unwinders'.*" \
> +    "no suitable unwinders should be found"
> +
> +# Reenable all unwinders.
> +gdb_test_no_output "maint frame-unwinder enable -all"
> +check_unwinder_class "\\w+" "Y" \
> +    "all unwinders should be re-enabled"
> +
> +# Check that we are able to get backtraces once again.
> +gdb_test "backtrace" ".0\\s+main .. at.*" \
> +    "we can get usable backtraces again"
> +
> +# Check if we can disable an unwinder based on the name.
> +check_unwinder_state "dummy" "Y"
> +gdb_test_no_output "maint frame-unwinder disable -name dummy"
> +check_unwinder_state "dummy" "N"
> +# And verify what happens if you try to disable it again.
> +gdb_test "maint frame-unwinder disable -name dummy" \
> +    "unwinder dummy is already disabled" \
> +    "disable already disabled unwinder"
> +check_unwinder_state "dummy" "N" "dummy should continue disabled"
> +
> +foreach class {GDB ARCH DEBUGINFO EXTENSION} {
> +    # Disable all unwinders of type CLASS, and check that the command worked.
> +    gdb_test_no_output "maint frame-unwinder disable ${class}"
> +    check_unwinder_class "${class}" "N"
> +}
> +
> +# Now check if we are able to enable a single unwinder, and what happens if we
> +# enable it twice.
> +gdb_test_no_output "maint frame-unwinder enable -name dummy"
> +check_unwinder_state "dummy" "Y" "successfully enabled dummy unwinder"
> +gdb_test "maint frame-unwinder enable -name dummy" \
> +    "unwinder dummy is already enabled" \
> +    "enable already enabled unwinder"
> +check_unwinder_state "dummy" "Y" "dummy should continue enabled"
> +
> +foreach class {GDB ARCH DEBUGINFO EXTENSION} {
> +    # Enable all unwinders of type CLASS, and check that the command worked,
> +    # using "-class" option to ensure it works.  Should make no difference.
> +    gdb_test_no_output "maint frame-unwinder enable -class ${class}"
> +    check_unwinder_class "${class}" "Y"
> +}
> diff --git a/gdb/testsuite/gdb.base/maint.exp b/gdb/testsuite/gdb.base/maint.exp
> index 2c58ffa36c5..ae7ad0787e6 100644
> --- a/gdb/testsuite/gdb.base/maint.exp
> +++ b/gdb/testsuite/gdb.base/maint.exp
> @@ -454,10 +454,6 @@ gdb_test_no_output "maint info line-table xxx.c" \
>  
>  set timeout $oldtimeout
>  
> -# Just check that the DWARF unwinders control flag is visible.
> -gdb_test "maint show dwarf unwinders" \
> -    "The DWARF stack unwinders are currently (on|off)\\."
> -
>  #============test help on maint commands
>  
>  test_prefix_command_help {"maint info" "maintenance info"} {
> -- 
> 2.47.0

---

diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
index 1417651108f..f3019b7ec18 100644
--- a/gdb/frame-unwind.c
+++ b/gdb/frame-unwind.c
@@ -40,6 +40,7 @@ static const char * unwind_class_conversion[] =
   "EXTENSION",
   "DEBUGINFO",
   "ARCH",
+  nullptr
 };
 
 /* Default sniffers, that must always be the first in the unwinder list,
@@ -579,6 +580,29 @@ enable_disable_frame_unwinders (const char *args, int from_tty, bool enable)
   reinit_frame_cache ();
 }
 
+/* Completer for the "maint frame-unwinder enable|disable" commands.  */
+
+static void
+enable_disable_frame_unwinders_completer (struct cmd_list_element *ignore,
+					  completion_tracker &tracker,
+					  const char *text,
+					  const char */*word*/)
+{
+  maint_frame_unwind_options opts;
+  const auto group = make_frame_unwind_enable_disable_options (&opts);
+
+  const char *start = text;
+  if (gdb::option::complete_options
+      (tracker, &text, gdb::option::PROCESS_OPTIONS_UNKNOWN_IS_OPERAND, group))
+    return;
+
+  /* Only complete a class name as a stand-alone operand when no options
+     are given.  */
+  if (start == text)
+    complete_on_enum (tracker, unwind_class_conversion, text, text);
+  return;
+}
+
 /* Implement "maint frame-unwinder disable" command.  */
 static void
 maintenance_disable_frame_unwinders (const char *args, int from_tty)
@@ -613,8 +637,9 @@ Unwinders are listed starting with the highest priority."),
 			_("Commands handling frame unwinders."),
 			&maint_frame_unwinder, 0, &maintenancelist);
 
-  add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
-	   _("\
+  cmd_list_element *c
+    = add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
+	       _("\
 Disable one or more frame unwinder(s).\n\
 Usage: maint frame-unwinder disable [-all | -name NAME | [-class] CLASS]\n\
 \n\
@@ -628,10 +653,13 @@ These are the meanings of the options:\n\
 \t\tARCH      - Unwinders that use architecture-specific information;\n\
 \n\
 UNWINDER and NAME are case insensitive."),
-	   &maint_frame_unwinder);
+	       &maint_frame_unwinder);
+  set_cmd_completer_handle_brkchars (c,
+				     enable_disable_frame_unwinders_completer);
 
-  add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
-	   _("\
+  c =
+    add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
+	     _("\
 Enable one or more frame unwinder(s).\n\
 Usage: maint frame-unwinder enable [-all | -name NAME | [-class] CLASS]\n\
 \n\
@@ -645,5 +673,7 @@ These are the meanings of the options:\n\
 \t\tARCH      - Unwinders that use architecture-specific information;\n\
 \n\
 UNWINDER and NAME are case insensitive."),
-	   &maint_frame_unwinder);
+	     &maint_frame_unwinder);
+  set_cmd_completer_handle_brkchars (c,
+				     enable_disable_frame_unwinders_completer);
 }
  

Guinevere Larsen <guinevere@redhat.com> writes:

> Sometimes, in the GDB testsuite, we want to test the ability of specific
> unwinders to handle some piece of code. Usually this is done by trying
> to outsmart GDB, or by coercing the compiler to remove information that
> GDB would rely on.  Both approaches have problems as GDB gets smarter
> with time, and that compilers might differ in version and behavior, or
> simply introduce new useful information. This was requested back in 2003
> in PR backtrace/8434.
>
> To improve our ability to thoroughly test GDB, this patch introduces a
> new maintenance command that allows a user to disable some unwinders,
> based on either the name of the unwinder or on its class. With this
> change, it will now be possible for GDB to not find any frame unwinders
> for a given frame, which would previously cause GDB to assert. GDB will
> now check if any frame unwinder has been disabled, and if some has, it
> will just error out instead of asserting.
>
> Unwinders can be disabled or re-enabled in 3 different ways:
> * Disabling/enabling all at once (using '-all').
> * By specifying an unwinder class to be disabled (option '-class').
> * By specifying the name of an unwinder (option '-name').
>
> If you give no options to the command, GDB assumes the input is an
> unwinder class. '-class' would make no difference if used, is just here
> for completeness.
>
> This command is meant to be used once the inferior is already at the
> desired location for the test. An example session would be:
>
> (gdb) start
> Temporary breakpoint 1, main () at omp.c:17
> 17          func();
> (gdb) maint frame-unwinder disable ARCH
> (gdb) bt
> \#0  main () at omp.c:17
> (gdb) maint frame-unwinder enable ARCH
> (gdb) cont
> Continuing.
>
> This commit is a more generic version of commit 3c3bb0580be0,
> and so, based on the final paragraph of the commit message:
>     gdb: Add switch to disable DWARF stack unwinders
> <...>
>     If in the future we find ourselves adding more switches to disable
>     different unwinders, then we should probably move to a more generic
>     solution, and remove this patch.
> this patch also reverts 3c3bb0580be0
>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=8434
> Reviewed-By: Eli Zaretskii <eliz@gnu.org>
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
> ---
>  gdb/NEWS                                      |  17 ++
>  gdb/doc/gdb.texinfo                           |  49 ++--
>  gdb/dwarf2/frame-tailcall.c                   |   3 -
>  gdb/dwarf2/frame.c                            |  30 ---
>  gdb/dwarf2/frame.h                            |   6 -
>  gdb/frame-unwind.c                            | 237 +++++++++++++++++-
>  gdb/frame-unwind.h                            |   9 +
>  .../gdb.base/frame-info-consistent.exp        |   8 +-
>  gdb/testsuite/gdb.base/frame-unwind-disable.c |  22 ++
>  .../gdb.base/frame-unwind-disable.exp         | 137 ++++++++++
>  gdb/testsuite/gdb.base/maint.exp              |   4 -
>  11 files changed, 437 insertions(+), 85 deletions(-)
>  create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.c
>  create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.exp
>
> diff --git a/gdb/NEWS b/gdb/NEWS
> index 245b355669a..ef3317c11cb 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -125,6 +125,13 @@ maintenance info blocks [ADDRESS]
>    are listed starting at the inner global block out to the most inner
>    block.
>  
> +maintenance frame-unwinder disable [-all | -name NAME | [-class] CLASS]
> +maintenance frame-unwinder enable [-all | -name NAME | [-class] CLASS]
> +  Enable or disable frame unwinders.  This is only meant to be used when
> +  testing unwinders themselves, and you want to ensure that a fallback
> +  algorithm won't obscure a regression.  GDB is not expected to behave
> +  well if you try to execute the inferior with unwinders disabled.
> +
>  info missing-objfile-handlers
>    List all the registered missing-objfile handlers.
>  
> @@ -167,6 +174,16 @@ maintenance print remote-registers
>  mainenance info frame-unwinders
>    Add a CLASS column to the output.  This class is a somewhat arbitrary
>    grouping of unwinders, based on which area of GDB adds the unwinder.
> +  Also add an ENABLED column, that will show if the unwinder is enabled
> +  or not.
> +
> +maintenance set dwarf unwinders (on|off)
> +  This command has been removed because the same functionality can be
> +  achieved with maint frame-unwinder (enable|disable) DEBUGINFO.
> +
> +maintenance show dwarf unwinders
> +  This command has been removed since the functionality can be achieved
> +  by checking the last column of maint info frame-unwinders.
>  
>  show configuration
>    Now includes the version of GNU Readline library that GDB is using.
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index 115c1f46b7f..10e6654a03b 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -42210,31 +42210,6 @@ On hosts without threading, or where worker threads have been disabled
>  at runtime, this setting has no effect, as DWARF reading is always
>  done on the main thread, and is therefore always synchronous.
>  
> -@kindex maint set dwarf unwinders
> -@kindex maint show dwarf unwinders
> -@item maint set dwarf unwinders
> -@itemx maint show dwarf unwinders
> -Control use of the DWARF frame unwinders.
> -
> -@cindex DWARF frame unwinders
> -Many targets that support DWARF debugging use @value{GDBN}'s DWARF
> -frame unwinders to build the backtrace.  Many of these targets will
> -also have a second mechanism for building the backtrace for use in
> -cases where DWARF information is not available, this second mechanism
> -is often an analysis of a function's prologue.
> -
> -In order to extend testing coverage of the second level stack
> -unwinding mechanisms it is helpful to be able to disable the DWARF
> -stack unwinders, this can be done with this switch.
> -
> -In normal use of @value{GDBN} disabling the DWARF unwinders is not
> -advisable, there are cases that are better handled through DWARF than
> -prologue analysis, and the debug experience is likely to be better
> -with the DWARF frame unwinders enabled.
> -
> -If DWARF frame unwinders are not supported for a particular target
> -architecture, then enabling this flag does not cause them to be used.
> -
>  @kindex maint info frame-unwinders
>  @item maint info frame-unwinders
>  List the frame unwinders currently in effect, starting with the highest
> @@ -42252,6 +42227,30 @@ Unwinders installed by debug information readers.
>  Unwinders installed by the architecture specific code.
>  @end table
>  
> +@kindex maint frame-unwinder disable
> +@kindex maint frame-unwinder enable
> +@item maint frame-unwinder disable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
> +@item maint frame-unwinder enable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
> +Disable or enable frame unwinders.  This is meant only as a testing tool, and
> +@value{GDBN} is not guaranteed to work properly if it is unable to find
> +valid frame unwinders.
> +
> +The meaning of each of the invocations are as follows:
> +
> +@table @samp
> +@item @code{-all}
> +Disable or enable all unwinders.
> +@item @code{-name} @var{name}
> +@var{name} is the exact name of the unwinder to be disabled or enabled.
> +@item [@code{-class}] @var{class}
> +@var{class} is the class of frame unwinders to be disabled or enabled.
> +The class may include the prefix @code{FRAME_UNWINDER_}, but it is not
> +required.
> +@end table
> +
> +@var{name} and @var{class} are always case insensitive.  If no option
> +starting wth @code{-} is given, @value{GDBN} assumes @code{-class}.
> +
>  @kindex maint set worker-threads
>  @kindex maint show worker-threads
>  @item maint set worker-threads
> diff --git a/gdb/dwarf2/frame-tailcall.c b/gdb/dwarf2/frame-tailcall.c
> index 54813d00b03..2d7ab740f62 100644
> --- a/gdb/dwarf2/frame-tailcall.c
> +++ b/gdb/dwarf2/frame-tailcall.c
> @@ -321,9 +321,6 @@ tailcall_frame_sniffer (const struct frame_unwind *self,
>    int next_levels;
>    struct tailcall_cache *cache;
>  
> -  if (!dwarf2_frame_unwinders_enabled_p)
> -    return 0;
> -
>    /* Inner tail call element does not make sense for a sentinel frame.  */
>    next_frame = get_next_frame (this_frame);
>    if (next_frame == NULL)
> diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
> index 85e1d59bc09..e0e8eb5dbec 100644
> --- a/gdb/dwarf2/frame.c
> +++ b/gdb/dwarf2/frame.c
> @@ -183,9 +183,6 @@ static ULONGEST read_encoded_value (struct comp_unit *unit, gdb_byte encoding,
>  				    unrelocated_addr func_base);
>  
>  
> -/* See dwarf2/frame.h.  */
> -bool dwarf2_frame_unwinders_enabled_p = true;
> -
>  /* Store the length the expression for the CFA in the `cfa_reg' field,
>     which is unused in that case.  */
>  #define cfa_exp_len cfa_reg
> @@ -1306,9 +1303,6 @@ static int
>  dwarf2_frame_sniffer (const struct frame_unwind *self,
>  		      const frame_info_ptr &this_frame, void **this_cache)
>  {
> -  if (!dwarf2_frame_unwinders_enabled_p)
> -    return 0;
> -
>    /* Grab an address that is guaranteed to reside somewhere within the
>       function.  get_frame_pc(), with a no-return next function, can
>       end up returning something past the end of this function's body.
> @@ -2253,34 +2247,10 @@ dwarf2_build_frame_info (struct objfile *objfile)
>    set_comp_unit (objfile, unit.release ());
>  }
>  
> -/* Handle 'maintenance show dwarf unwinders'.  */
> -
> -static void
> -show_dwarf_unwinders_enabled_p (struct ui_file *file, int from_tty,
> -				struct cmd_list_element *c,
> -				const char *value)
> -{
> -  gdb_printf (file,
> -	      _("The DWARF stack unwinders are currently %s.\n"),
> -	      value);
> -}
> -
>  void _initialize_dwarf2_frame ();
>  void
>  _initialize_dwarf2_frame ()
>  {
> -  add_setshow_boolean_cmd ("unwinders", class_obscure,
> -			   &dwarf2_frame_unwinders_enabled_p , _("\
> -Set whether the DWARF stack frame unwinders are used."), _("\
> -Show whether the DWARF stack frame unwinders are used."), _("\
> -When enabled the DWARF stack frame unwinders can be used for architectures\n\
> -that support the DWARF unwinders.  Enabling the DWARF unwinders for an\n\
> -architecture that doesn't support them will have no effect."),
> -			   NULL,
> -			   show_dwarf_unwinders_enabled_p,
> -			   &set_dwarf_cmdlist,
> -			   &show_dwarf_cmdlist);
> -
>  #if GDB_SELF_TEST
>    selftests::register_test_foreach_arch ("execute_cfa_program",
>  					 selftests::execute_cfa_program_test);
> diff --git a/gdb/dwarf2/frame.h b/gdb/dwarf2/frame.h
> index 2167310fbdf..fe2d669a983 100644
> --- a/gdb/dwarf2/frame.h
> +++ b/gdb/dwarf2/frame.h
> @@ -198,12 +198,6 @@ struct dwarf2_frame_state
>    bool armcc_cfa_offsets_reversed = false;
>  };
>  
> -/* When this is true the DWARF frame unwinders can be used if they are
> -   registered with the gdbarch.  Not all architectures can or do use the
> -   DWARF unwinders.  Setting this to true on a target that does not
> -   otherwise support the DWARF unwinders has no effect.  */
> -extern bool dwarf2_frame_unwinders_enabled_p;
> -
>  /* Set the architecture-specific register state initialization
>     function for GDBARCH to INIT_REG.  */
>  
> diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
> index 3ab6af1c4da..968bb846402 100644
> --- a/gdb/frame-unwind.c
> +++ b/gdb/frame-unwind.c
> @@ -29,6 +29,7 @@
>  #include "gdbarch.h"
>  #include "dwarf2/frame-tailcall.h"
>  #include "cli/cli-cmds.h"
> +#include "cli/cli-option.h"
>  #include "inferior.h"
>  
>  /* Conversion list between the enum for frame_unwind_class and
> @@ -89,6 +90,20 @@ frame_unwinder_class_str (frame_unwind_class uclass)
>    return unwind_class_conversion[uclass];
>  }
>  
> +/* Case insensitive search for a frame_unwind_class based on the given
> +   string.  */
> +static enum frame_unwind_class
> +str_to_frame_unwind_class (const char *class_str)
> +{
> +  for (int i = 0; i < UNWIND_CLASS_NUMBER; i++)
> +    {
> +      if (strcasecmp (unwind_class_conversion[i], class_str) == 0)
> +	return (frame_unwind_class) i;
> +    }
> +
> +  error (_("Unknown frame unwind class: %s"), class_str);
> +}
> +
>  void
>  frame_unwind_prepend_unwinder (struct gdbarch *gdbarch,
>  				const struct frame_unwind *unwinder)
> @@ -175,27 +190,46 @@ frame_unwind_find_by_frame (const frame_info_ptr &this_frame, void **this_cache)
>    FRAME_SCOPED_DEBUG_ENTER_EXIT;
>    frame_debug_printf ("this_frame=%d", frame_relative_level (this_frame));
>  
> -  const struct frame_unwind *unwinder_from_target;
> +  /* If we see a disabled unwinder, we assume some test is being run on
> +     GDB, and we don't want to internal_error at the end of this function.  */
> +  bool seen_disabled_unwinder = false;
> +  /* Lambda to factor out the logic of checking if an unwinder is enabled,
> +     testing it and otherwise recording if we saw a disable unwinder.  */
> +  auto test_unwinder = [&] (const struct frame_unwind *unwinder)
> +    {
> +      if (unwinder == nullptr)
> +	return false;
> +
> +      if (!unwinder->enabled ())
> +	{
> +	  seen_disabled_unwinder = true;
> +	  return false;
> +	}
> +
> +      return frame_unwind_try_unwinder (this_frame,
> +					this_cache,
> +					unwinder);
> +    };
>  
> -  unwinder_from_target = target_get_unwinder ();
> -  if (unwinder_from_target != NULL
> -      && frame_unwind_try_unwinder (this_frame, this_cache,
> -				   unwinder_from_target))
> +  if (test_unwinder (target_get_unwinder ()))
>      return;
>  
> -  unwinder_from_target = target_get_tailcall_unwinder ();
> -  if (unwinder_from_target != NULL
> -      && frame_unwind_try_unwinder (this_frame, this_cache,
> -				   unwinder_from_target))
> +  if (test_unwinder (target_get_tailcall_unwinder ()))
>      return;
>  
>    struct gdbarch *gdbarch = get_frame_arch (this_frame);
>    std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>    for (auto unwinder : *table)
> -    if (frame_unwind_try_unwinder (this_frame, this_cache, unwinder))
> -      return;
> +    {
> +      if (test_unwinder (unwinder))
> +	return;
> +    }
>  
> -  internal_error (_("frame_unwind_find_by_frame failed"));
> +  if (seen_disabled_unwinder)
> +    error (_("Required frame unwinder may have been disabled"
> +	     ", see 'maint info frame-unwinders'"));
> +  else
> +    internal_error (_("frame_unwind_find_by_frame failed"));
>  }
>  
>  /* A default frame sniffer which always accepts the frame.  Used by
> @@ -394,10 +428,11 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>    std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>  
>    ui_out *uiout = current_uiout;
> -  ui_out_emit_table table_emitter (uiout, 3, -1, "FrameUnwinders");
> +  ui_out_emit_table table_emitter (uiout, 4, -1, "FrameUnwinders");
>    uiout->table_header (27, ui_left, "name", "Name");
>    uiout->table_header (25, ui_left, "type", "Type");
>    uiout->table_header (9, ui_left, "class", "Class");
> +  uiout->table_header (8, ui_left, "enabled", "Enabled");
>    uiout->table_body ();
>  
>    for (auto unwinder : *table)
> @@ -407,10 +442,145 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>        uiout->field_string ("type", frame_type_str (unwinder->type ()));
>        uiout->field_string ("class", frame_unwinder_class_str (
>  					unwinder->unwinder_class ()));
> +      uiout->field_string ("enabled", unwinder->enabled () ? "Y" : "N");
>        uiout->text ("\n");
>      }
>  }
>  
> +/* Options for disabling frame unwinders.  */
> +struct maint_frame_unwind_options
> +{
> +  std::string unwinder_name;
> +  const char *unwinder_class = nullptr;
> +  bool all = false;
> +};
> +
> +static const gdb::option::option_def maint_frame_unwind_opt_defs[] = {
> +
> +  gdb::option::flag_option_def<maint_frame_unwind_options> {
> +    "all",
> +    [] (maint_frame_unwind_options *opt) { return &opt->all; },
> +    nullptr,
> +    N_("Change the state of all unwinders")

I think for flag_option_def, this should be:

  gdb::option::flag_option_def<maint_frame_unwind_options> {
    "all",
    [] (maint_frame_unwind_options *opt) { return &opt->all; },
    N_("Change the state of all unwinders")
  }

dropping the 'nullptr'.  If/when we use %OPTIONS% this will then print
that 'Change the state of all unwinders' text as the description of this
option.

Thanks,
Andrew
  

On 1/16/25 9:06 AM, Andrew Burgess wrote:
> Guinevere Larsen <guinevere@redhat.com> writes:
>
>> Sometimes, in the GDB testsuite, we want to test the ability of specific
>> unwinders to handle some piece of code. Usually this is done by trying
>> to outsmart GDB, or by coercing the compiler to remove information that
>> GDB would rely on.  Both approaches have problems as GDB gets smarter
>> with time, and that compilers might differ in version and behavior, or
>> simply introduce new useful information. This was requested back in 2003
>> in PR backtrace/8434.
>>
>> To improve our ability to thoroughly test GDB, this patch introduces a
>> new maintenance command that allows a user to disable some unwinders,
>> based on either the name of the unwinder or on its class. With this
>> change, it will now be possible for GDB to not find any frame unwinders
>> for a given frame, which would previously cause GDB to assert. GDB will
>> now check if any frame unwinder has been disabled, and if some has, it
>> will just error out instead of asserting.
>>
>> Unwinders can be disabled or re-enabled in 3 different ways:
>> * Disabling/enabling all at once (using '-all').
>> * By specifying an unwinder class to be disabled (option '-class').
>> * By specifying the name of an unwinder (option '-name').
>>
>> If you give no options to the command, GDB assumes the input is an
>> unwinder class. '-class' would make no difference if used, is just here
>> for completeness.
>>
>> This command is meant to be used once the inferior is already at the
>> desired location for the test. An example session would be:
>>
>> (gdb) start
>> Temporary breakpoint 1, main () at omp.c:17
>> 17          func();
>> (gdb) maint frame-unwinder disable ARCH
>> (gdb) bt
>> \#0  main () at omp.c:17
>> (gdb) maint frame-unwinder enable ARCH
>> (gdb) cont
>> Continuing.
>>
>> This commit is a more generic version of commit 3c3bb0580be0,
>> and so, based on the final paragraph of the commit message:
>>      gdb: Add switch to disable DWARF stack unwinders
>> <...>
>>      If in the future we find ourselves adding more switches to disable
>>      different unwinders, then we should probably move to a more generic
>>      solution, and remove this patch.
>> this patch also reverts 3c3bb0580be0
>>
>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=8434
>> Reviewed-By: Eli Zaretskii <eliz@gnu.org>
>> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
>> ---
>>   gdb/NEWS                                      |  17 ++
>>   gdb/doc/gdb.texinfo                           |  49 ++--
>>   gdb/dwarf2/frame-tailcall.c                   |   3 -
>>   gdb/dwarf2/frame.c                            |  30 ---
>>   gdb/dwarf2/frame.h                            |   6 -
>>   gdb/frame-unwind.c                            | 237 +++++++++++++++++-
>>   gdb/frame-unwind.h                            |   9 +
>>   .../gdb.base/frame-info-consistent.exp        |   8 +-
>>   gdb/testsuite/gdb.base/frame-unwind-disable.c |  22 ++
>>   .../gdb.base/frame-unwind-disable.exp         | 137 ++++++++++
>>   gdb/testsuite/gdb.base/maint.exp              |   4 -
>>   11 files changed, 437 insertions(+), 85 deletions(-)
>>   create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.c
>>   create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.exp
>>
>> diff --git a/gdb/NEWS b/gdb/NEWS
>> index 245b355669a..ef3317c11cb 100644
>> --- a/gdb/NEWS
>> +++ b/gdb/NEWS
>> @@ -125,6 +125,13 @@ maintenance info blocks [ADDRESS]
>>     are listed starting at the inner global block out to the most inner
>>     block.
>>   
>> +maintenance frame-unwinder disable [-all | -name NAME | [-class] CLASS]
>> +maintenance frame-unwinder enable [-all | -name NAME | [-class] CLASS]
>> +  Enable or disable frame unwinders.  This is only meant to be used when
>> +  testing unwinders themselves, and you want to ensure that a fallback
>> +  algorithm won't obscure a regression.  GDB is not expected to behave
>> +  well if you try to execute the inferior with unwinders disabled.
>> +
>>   info missing-objfile-handlers
>>     List all the registered missing-objfile handlers.
>>   
>> @@ -167,6 +174,16 @@ maintenance print remote-registers
>>   mainenance info frame-unwinders
>>     Add a CLASS column to the output.  This class is a somewhat arbitrary
>>     grouping of unwinders, based on which area of GDB adds the unwinder.
>> +  Also add an ENABLED column, that will show if the unwinder is enabled
>> +  or not.
>> +
>> +maintenance set dwarf unwinders (on|off)
>> +  This command has been removed because the same functionality can be
>> +  achieved with maint frame-unwinder (enable|disable) DEBUGINFO.
>> +
>> +maintenance show dwarf unwinders
>> +  This command has been removed since the functionality can be achieved
>> +  by checking the last column of maint info frame-unwinders.
>>   
>>   show configuration
>>     Now includes the version of GNU Readline library that GDB is using.
>> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
>> index 115c1f46b7f..10e6654a03b 100644
>> --- a/gdb/doc/gdb.texinfo
>> +++ b/gdb/doc/gdb.texinfo
>> @@ -42210,31 +42210,6 @@ On hosts without threading, or where worker threads have been disabled
>>   at runtime, this setting has no effect, as DWARF reading is always
>>   done on the main thread, and is therefore always synchronous.
>>   
>> -@kindex maint set dwarf unwinders
>> -@kindex maint show dwarf unwinders
>> -@item maint set dwarf unwinders
>> -@itemx maint show dwarf unwinders
>> -Control use of the DWARF frame unwinders.
>> -
>> -@cindex DWARF frame unwinders
>> -Many targets that support DWARF debugging use @value{GDBN}'s DWARF
>> -frame unwinders to build the backtrace.  Many of these targets will
>> -also have a second mechanism for building the backtrace for use in
>> -cases where DWARF information is not available, this second mechanism
>> -is often an analysis of a function's prologue.
>> -
>> -In order to extend testing coverage of the second level stack
>> -unwinding mechanisms it is helpful to be able to disable the DWARF
>> -stack unwinders, this can be done with this switch.
>> -
>> -In normal use of @value{GDBN} disabling the DWARF unwinders is not
>> -advisable, there are cases that are better handled through DWARF than
>> -prologue analysis, and the debug experience is likely to be better
>> -with the DWARF frame unwinders enabled.
>> -
>> -If DWARF frame unwinders are not supported for a particular target
>> -architecture, then enabling this flag does not cause them to be used.
>> -
>>   @kindex maint info frame-unwinders
>>   @item maint info frame-unwinders
>>   List the frame unwinders currently in effect, starting with the highest
>> @@ -42252,6 +42227,30 @@ Unwinders installed by debug information readers.
>>   Unwinders installed by the architecture specific code.
>>   @end table
>>   
>> +@kindex maint frame-unwinder disable
>> +@kindex maint frame-unwinder enable
>> +@item maint frame-unwinder disable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
>> +@item maint frame-unwinder enable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
>> +Disable or enable frame unwinders.  This is meant only as a testing tool, and
>> +@value{GDBN} is not guaranteed to work properly if it is unable to find
>> +valid frame unwinders.
>> +
>> +The meaning of each of the invocations are as follows:
>> +
>> +@table @samp
>> +@item @code{-all}
>> +Disable or enable all unwinders.
>> +@item @code{-name} @var{name}
>> +@var{name} is the exact name of the unwinder to be disabled or enabled.
>> +@item [@code{-class}] @var{class}
>> +@var{class} is the class of frame unwinders to be disabled or enabled.
>> +The class may include the prefix @code{FRAME_UNWINDER_}, but it is not
>> +required.
>> +@end table
>> +
>> +@var{name} and @var{class} are always case insensitive.  If no option
>> +starting wth @code{-} is given, @value{GDBN} assumes @code{-class}.
>> +
>>   @kindex maint set worker-threads
>>   @kindex maint show worker-threads
>>   @item maint set worker-threads
>> diff --git a/gdb/dwarf2/frame-tailcall.c b/gdb/dwarf2/frame-tailcall.c
>> index 54813d00b03..2d7ab740f62 100644
>> --- a/gdb/dwarf2/frame-tailcall.c
>> +++ b/gdb/dwarf2/frame-tailcall.c
>> @@ -321,9 +321,6 @@ tailcall_frame_sniffer (const struct frame_unwind *self,
>>     int next_levels;
>>     struct tailcall_cache *cache;
>>   
>> -  if (!dwarf2_frame_unwinders_enabled_p)
>> -    return 0;
>> -
>>     /* Inner tail call element does not make sense for a sentinel frame.  */
>>     next_frame = get_next_frame (this_frame);
>>     if (next_frame == NULL)
>> diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
>> index 85e1d59bc09..e0e8eb5dbec 100644
>> --- a/gdb/dwarf2/frame.c
>> +++ b/gdb/dwarf2/frame.c
>> @@ -183,9 +183,6 @@ static ULONGEST read_encoded_value (struct comp_unit *unit, gdb_byte encoding,
>>   				    unrelocated_addr func_base);
>>   
>>   
>> -/* See dwarf2/frame.h.  */
>> -bool dwarf2_frame_unwinders_enabled_p = true;
>> -
>>   /* Store the length the expression for the CFA in the `cfa_reg' field,
>>      which is unused in that case.  */
>>   #define cfa_exp_len cfa_reg
>> @@ -1306,9 +1303,6 @@ static int
>>   dwarf2_frame_sniffer (const struct frame_unwind *self,
>>   		      const frame_info_ptr &this_frame, void **this_cache)
>>   {
>> -  if (!dwarf2_frame_unwinders_enabled_p)
>> -    return 0;
>> -
>>     /* Grab an address that is guaranteed to reside somewhere within the
>>        function.  get_frame_pc(), with a no-return next function, can
>>        end up returning something past the end of this function's body.
>> @@ -2253,34 +2247,10 @@ dwarf2_build_frame_info (struct objfile *objfile)
>>     set_comp_unit (objfile, unit.release ());
>>   }
>>   
>> -/* Handle 'maintenance show dwarf unwinders'.  */
>> -
>> -static void
>> -show_dwarf_unwinders_enabled_p (struct ui_file *file, int from_tty,
>> -				struct cmd_list_element *c,
>> -				const char *value)
>> -{
>> -  gdb_printf (file,
>> -	      _("The DWARF stack unwinders are currently %s.\n"),
>> -	      value);
>> -}
>> -
>>   void _initialize_dwarf2_frame ();
>>   void
>>   _initialize_dwarf2_frame ()
>>   {
>> -  add_setshow_boolean_cmd ("unwinders", class_obscure,
>> -			   &dwarf2_frame_unwinders_enabled_p , _("\
>> -Set whether the DWARF stack frame unwinders are used."), _("\
>> -Show whether the DWARF stack frame unwinders are used."), _("\
>> -When enabled the DWARF stack frame unwinders can be used for architectures\n\
>> -that support the DWARF unwinders.  Enabling the DWARF unwinders for an\n\
>> -architecture that doesn't support them will have no effect."),
>> -			   NULL,
>> -			   show_dwarf_unwinders_enabled_p,
>> -			   &set_dwarf_cmdlist,
>> -			   &show_dwarf_cmdlist);
>> -
>>   #if GDB_SELF_TEST
>>     selftests::register_test_foreach_arch ("execute_cfa_program",
>>   					 selftests::execute_cfa_program_test);
>> diff --git a/gdb/dwarf2/frame.h b/gdb/dwarf2/frame.h
>> index 2167310fbdf..fe2d669a983 100644
>> --- a/gdb/dwarf2/frame.h
>> +++ b/gdb/dwarf2/frame.h
>> @@ -198,12 +198,6 @@ struct dwarf2_frame_state
>>     bool armcc_cfa_offsets_reversed = false;
>>   };
>>   
>> -/* When this is true the DWARF frame unwinders can be used if they are
>> -   registered with the gdbarch.  Not all architectures can or do use the
>> -   DWARF unwinders.  Setting this to true on a target that does not
>> -   otherwise support the DWARF unwinders has no effect.  */
>> -extern bool dwarf2_frame_unwinders_enabled_p;
>> -
>>   /* Set the architecture-specific register state initialization
>>      function for GDBARCH to INIT_REG.  */
>>   
>> diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
>> index 3ab6af1c4da..968bb846402 100644
>> --- a/gdb/frame-unwind.c
>> +++ b/gdb/frame-unwind.c
>> @@ -29,6 +29,7 @@
>>   #include "gdbarch.h"
>>   #include "dwarf2/frame-tailcall.h"
>>   #include "cli/cli-cmds.h"
>> +#include "cli/cli-option.h"
>>   #include "inferior.h"
>>   
>>   /* Conversion list between the enum for frame_unwind_class and
>> @@ -89,6 +90,20 @@ frame_unwinder_class_str (frame_unwind_class uclass)
>>     return unwind_class_conversion[uclass];
>>   }
>>   
>> +/* Case insensitive search for a frame_unwind_class based on the given
>> +   string.  */
>> +static enum frame_unwind_class
>> +str_to_frame_unwind_class (const char *class_str)
>> +{
>> +  for (int i = 0; i < UNWIND_CLASS_NUMBER; i++)
>> +    {
>> +      if (strcasecmp (unwind_class_conversion[i], class_str) == 0)
>> +	return (frame_unwind_class) i;
>> +    }
>> +
>> +  error (_("Unknown frame unwind class: %s"), class_str);
>> +}
>> +
>>   void
>>   frame_unwind_prepend_unwinder (struct gdbarch *gdbarch,
>>   				const struct frame_unwind *unwinder)
>> @@ -175,27 +190,46 @@ frame_unwind_find_by_frame (const frame_info_ptr &this_frame, void **this_cache)
>>     FRAME_SCOPED_DEBUG_ENTER_EXIT;
>>     frame_debug_printf ("this_frame=%d", frame_relative_level (this_frame));
>>   
>> -  const struct frame_unwind *unwinder_from_target;
>> +  /* If we see a disabled unwinder, we assume some test is being run on
>> +     GDB, and we don't want to internal_error at the end of this function.  */
>> +  bool seen_disabled_unwinder = false;
>> +  /* Lambda to factor out the logic of checking if an unwinder is enabled,
>> +     testing it and otherwise recording if we saw a disable unwinder.  */
>> +  auto test_unwinder = [&] (const struct frame_unwind *unwinder)
>> +    {
>> +      if (unwinder == nullptr)
>> +	return false;
>> +
>> +      if (!unwinder->enabled ())
>> +	{
>> +	  seen_disabled_unwinder = true;
>> +	  return false;
>> +	}
>> +
>> +      return frame_unwind_try_unwinder (this_frame,
>> +					this_cache,
>> +					unwinder);
>> +    };
>>   
>> -  unwinder_from_target = target_get_unwinder ();
>> -  if (unwinder_from_target != NULL
>> -      && frame_unwind_try_unwinder (this_frame, this_cache,
>> -				   unwinder_from_target))
>> +  if (test_unwinder (target_get_unwinder ()))
>>       return;
>>   
>> -  unwinder_from_target = target_get_tailcall_unwinder ();
>> -  if (unwinder_from_target != NULL
>> -      && frame_unwind_try_unwinder (this_frame, this_cache,
>> -				   unwinder_from_target))
>> +  if (test_unwinder (target_get_tailcall_unwinder ()))
>>       return;
>>   
>>     struct gdbarch *gdbarch = get_frame_arch (this_frame);
>>     std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>>     for (auto unwinder : *table)
>> -    if (frame_unwind_try_unwinder (this_frame, this_cache, unwinder))
>> -      return;
>> +    {
>> +      if (test_unwinder (unwinder))
>> +	return;
>> +    }
>>   
>> -  internal_error (_("frame_unwind_find_by_frame failed"));
>> +  if (seen_disabled_unwinder)
>> +    error (_("Required frame unwinder may have been disabled"
>> +	     ", see 'maint info frame-unwinders'"));
>> +  else
>> +    internal_error (_("frame_unwind_find_by_frame failed"));
>>   }
>>   
>>   /* A default frame sniffer which always accepts the frame.  Used by
>> @@ -394,10 +428,11 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>>     std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>>   
>>     ui_out *uiout = current_uiout;
>> -  ui_out_emit_table table_emitter (uiout, 3, -1, "FrameUnwinders");
>> +  ui_out_emit_table table_emitter (uiout, 4, -1, "FrameUnwinders");
>>     uiout->table_header (27, ui_left, "name", "Name");
>>     uiout->table_header (25, ui_left, "type", "Type");
>>     uiout->table_header (9, ui_left, "class", "Class");
>> +  uiout->table_header (8, ui_left, "enabled", "Enabled");
>>     uiout->table_body ();
>>   
>>     for (auto unwinder : *table)
>> @@ -407,10 +442,145 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>>         uiout->field_string ("type", frame_type_str (unwinder->type ()));
>>         uiout->field_string ("class", frame_unwinder_class_str (
>>   					unwinder->unwinder_class ()));
>> +      uiout->field_string ("enabled", unwinder->enabled () ? "Y" : "N");
>>         uiout->text ("\n");
>>       }
>>   }
>>   
>> +/* Options for disabling frame unwinders.  */
>> +struct maint_frame_unwind_options
>> +{
>> +  std::string unwinder_name;
>> +  const char *unwinder_class = nullptr;
>> +  bool all = false;
>> +};
>> +
>> +static const gdb::option::option_def maint_frame_unwind_opt_defs[] = {
>> +
>> +  gdb::option::flag_option_def<maint_frame_unwind_options> {
>> +    "all",
>> +    [] (maint_frame_unwind_options *opt) { return &opt->all; },
>> +    nullptr,
>> +    N_("Change the state of all unwinders")
>> +  },
>> +  gdb::option::string_option_def<maint_frame_unwind_options> {
>> +    "name",
>> +    [] (maint_frame_unwind_options *opt) { return &opt->unwinder_name; },
>> +    nullptr,
>> +    N_("The name of the unwinder to have its state changed")
>> +  },
>> +  gdb::option::enum_option_def<maint_frame_unwind_options> {
>> +    "class",
>> +    unwind_class_conversion,
>> +    [] (maint_frame_unwind_options *opt) { return &opt->unwinder_class; },
>> +    nullptr,
>> +    N_("The class of unwinders to have their states changed")
>> +  }
>> +};
>> +
>> +static inline gdb::option::option_def_group
>> +make_frame_unwind_enable_disable_options (maint_frame_unwind_options *opts)
>> +{
>> +  return {{maint_frame_unwind_opt_defs}, opts};
>> +}
>> +
>> +/* Helper function to both enable and disable frame unwinders.
>> +   If ENABLE is true, this call will be enabling unwinders,
>> +   otherwise the unwinders will be disabled.  */
>> +static void
>> +enable_disable_frame_unwinders (const char *args, int from_tty, bool enable)
>> +{
>> +  if (args == nullptr)
>> +    {
>> +      if (enable)
>> +	error (_("Specify which frame unwinder(s) should be enabled"));
>> +      else
>> +	error (_("Specify which frame unwinder(s) should be disabled"));
>> +    }
>> +
>> +  struct gdbarch* gdbarch = current_inferior ()->arch ();
>> +  std::vector<const frame_unwind *> *unwinder_list
>> +    = get_frame_unwind_table (gdbarch);
>> +
>> +  maint_frame_unwind_options opts;
>> +  gdb::option::process_options
>> +    (&args, gdb::option::PROCESS_OPTIONS_UNKNOWN_IS_ERROR,
>> +     make_frame_unwind_enable_disable_options (&opts));
>> +
>> +  if ((opts.all && !opts.unwinder_name.empty ())
>> +      || (opts.all && opts.unwinder_class != nullptr)
>> +      || (!opts.unwinder_name.empty () && opts.unwinder_class != nullptr))
>> +    error (_("Options are mutually exclusive"));
>> +
>> +  /* First see if the user wants to change all unwinders.  */
>> +  if (opts.all)
>> +    {
>> +      for (const frame_unwind *u : *unwinder_list)
>> +	u->set_enabled (enable);
>> +
>> +      reinit_frame_cache ();
>> +      return;
>> +    }
>> +
>> +  /* If user entered a specific unwinder name, handle it here.  If the
>> +     unwinder is already at the expected state, error out.  */
>> +  if (!opts.unwinder_name.empty ())
>> +    {
>> +      bool did_something = false;
>> +      for (const frame_unwind *unwinder : *unwinder_list)
>> +	{
>> +	  if (strcasecmp (unwinder->name (),
>> +			  opts.unwinder_name.c_str ()) == 0)
>> +	    {
>> +	      if (unwinder->enabled () == enable)
>> +		{
>> +		  if (unwinder->enabled ())
>> +		    error (_("unwinder %s is already enabled"),
>> +			     unwinder->name ());
>> +		  else
>> +		    error (_("unwinder %s is already disabled"),
>> +			     unwinder->name ());
>> +		}
>> +	      unwinder->set_enabled (enable);
>> +
>> +	      did_something = true;
>> +	      break;
>> +	    }
>> +	}
>> +      if (!did_something)
>> +	error (_("couldn't find unwinder named %s"),
>> +	       opts.unwinder_name.c_str ());
>> +    }
>> +  else
>> +    {
>> +      if (opts.unwinder_class == nullptr)
>> +	opts.unwinder_class = args;
>> +      enum frame_unwind_class dclass = str_to_frame_unwind_class
>> +	(opts.unwinder_class);
>> +      for (auto unwinder: *unwinder_list)
> I think you should stick with the form you use earlier:
>
>    (const frame_unwind *unwinder : *unwinder_list)
>
> But if you really want to stick with auto, then I think:
>
>   (const auto &unwinder : *unwinder_list)
>
> would be OK.
>
>
>> +	{
>> +	  if (unwinder->unwinder_class () == dclass)
>> +	    unwinder->set_enabled (enable);
>> +	}
>> +    }
>> +
>> +  reinit_frame_cache ();
>> +}
>> +
>> +/* Implement "maint frame-unwinder disable" command.  */
>> +static void
>> +maintenance_disable_frame_unwinders (const char *args, int from_tty)
>> +{
>> +  enable_disable_frame_unwinders (args, from_tty, false);
>> +}
>> +
>> +/* Implement "maint frame-unwinder enable" command.  */
>> +static void
>> +maintenance_enable_frame_unwinders (const char *args, int from_tty)
>> +{
>> +  enable_disable_frame_unwinders (args, from_tty, true);
>> +}
>> +
>>   void _initialize_frame_unwind ();
>>   void
>>   _initialize_frame_unwind ()
>> @@ -423,4 +593,45 @@ _initialize_frame_unwind ()
>>   List the frame unwinders currently in effect.\n\
>>   Unwinders are listed starting with the highest priority."),
>>   	   &maintenanceinfolist);
>> +
>> +  /* Add "maint frame-unwinder disable/enable".  */
>> +  static struct cmd_list_element *maint_frame_unwinder;
>> +
>> +  add_basic_prefix_cmd ("frame-unwinder", class_maintenance,
>> +			_("Commands handling frame unwinders."),
>> +			&maint_frame_unwinder, 0, &maintenancelist);
>> +
>> +  add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
>> +	   _("\
>> +Disable one or more frame unwinder(s).\n\
>> +Usage: maint frame-unwinder disable [-all | -name NAME | [-class] CLASS]\n\
>> +\n\
>> +These are the meanings of the options:\n\
>> +\t-all    - All available unwinders will be disabled\n\
>> +\t-name   - NAME is the exact name of the frame unwinder to be disabled\n\
>> +\t-class  - CLASS is the class of unwinders to be disabled. Valid classes are:\n\
>> +\t\tGDB       - Unwinders added by GDB core;\n\
>> +\t\tEXTENSION - Unwinders added by extension languages;\n\
>> +\t\tDEBUGINFO - Unwinders that handle debug information;\n\
>> +\t\tARCH      - Unwinders that use architecture-specific information;\n\
>> +\n\
>> +UNWINDER and NAME are case insensitive."),
>> +	   &maint_frame_unwinder);
>> +
>> +  add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
>> +	   _("\
>> +Enable one or more frame unwinder(s).\n\
>> +Usage: maint frame-unwinder enable [-all | -name NAME | [-class] CLASS]\n\
>> +\n\
>> +These are the meanings of the options:\n\
>> +\t-all    - All available unwinders will be enabled\n\
>> +\t-name   - NAME is the exact name of the frame unwinder to be enabled\n\
>> +\t-class  - CLASS is the class of unwinders to be enabled. Valid classes are:\n\
>> +\t\tGDB       - Unwinders added by GDB core;\n\
>> +\t\tEXTENSION - Unwinders added by extension languages;\n\
>> +\t\tDEBUGINFO - Unwinders that handle debug information;\n\
>> +\t\tARCH      - Unwinders that use architecture-specific information;\n\
>> +\n\
>> +UNWINDER and NAME are case insensitive."),
>> +	   &maint_frame_unwinder);
>>   }
> At the bottom of this email you'll find a small patch which applies on
> top of this and adds some basic command completion.  It doesn't complete
> the NAMEs, I'm not sure if there's a good way to do that (yet).  It also
> doesn't switch the help text to use the %OPTIONS% mechanism, I tried
> that, but I think there may be some bugs with the formatting (I'll look
> into it), so I've left that off.
>
> You don't have to, we can add completion later, but I do think it would
> be good to merge the patch below with this one.  But it is up to you.
> Take a look and see what you think.
>
>> diff --git a/gdb/frame-unwind.h b/gdb/frame-unwind.h
>> index 13f18618d24..adf8b47982c 100644
>> --- a/gdb/frame-unwind.h
>> +++ b/gdb/frame-unwind.h
>> @@ -192,6 +192,12 @@ class frame_unwind
>>     const frame_data *unwind_data () const
>>     { return m_unwind_data; }
>>   
>> +  bool enabled () const
>> +  { return m_enabled; }
>> +
>> +  void set_enabled (bool state) const
>> +  { m_enabled = state; }
>> +
>>     /* Default stop_reason implementation.  It reports NO_REASON, unless the
>>        frame is the outermost.  */
>>   
>> @@ -245,6 +251,9 @@ class frame_unwind
>>     frame_unwind_class m_unwinder_class;
>>   
>>     const frame_data *m_unwind_data;
>> +
>> +  /* Whether this unwinder can be used when sniffing.  */
>> +  mutable bool m_enabled = true;
>>   };
>>   
>>   /* This is a legacy version of the frame unwinder.  The original struct
>> diff --git a/gdb/testsuite/gdb.base/frame-info-consistent.exp b/gdb/testsuite/gdb.base/frame-info-consistent.exp
>> index fe0cfad95bc..4f483111a91 100644
>> --- a/gdb/testsuite/gdb.base/frame-info-consistent.exp
>> +++ b/gdb/testsuite/gdb.base/frame-info-consistent.exp
>> @@ -95,11 +95,11 @@ proc compare_frames {frames} {
>>       }
>>   }
>>   
>> -proc test {dwarf_unwinder} {
>> +proc test {enable} {
>>   
>>       clean_restart $::binfile
>>   
>> -    gdb_test_no_output "maint set dwarf unwinder $dwarf_unwinder"
>> +    gdb_test_no_output "maint frame-unwinder $enable DEBUGINFO"
>>   
>>       if {![runto_main]} {
>>   	return 0
>> @@ -134,6 +134,6 @@ proc test {dwarf_unwinder} {
>>       }
>>   }
>>   
>> -foreach_with_prefix dwarf {"off" "on"} {
>> -    test $dwarf
>> +foreach_with_prefix action {"disable" "enable"} {
>> +    test $action
>>   }
>> diff --git a/gdb/testsuite/gdb.base/frame-unwind-disable.c b/gdb/testsuite/gdb.base/frame-unwind-disable.c
>> new file mode 100644
>> index 00000000000..bbcfb01316e
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.base/frame-unwind-disable.c
>> @@ -0,0 +1,22 @@
>> +/* This testcase is part of GDB, the GNU debugger.
>> +
>> +   Copyright 2024 Free Software Foundation, Inc.
> Remember to update the copyright date when rebasing.
>
>> +
>> +   This program is free software; you can redistribute it and/or modify
>> +   it under the terms of the GNU General Public License as published by
>> +   the Free Software Foundation; either version 3 of the License, or
>> +   (at your option) any later version.
>> +
>> +   This program is distributed in the hope that it will be useful,
>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> +   GNU General Public License for more details.
>> +
>> +   You should have received a copy of the GNU General Public License
>> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
>> +
>> +int
>> +main ()
>> +{
>> +  return 0;
>> +}
>> diff --git a/gdb/testsuite/gdb.base/frame-unwind-disable.exp b/gdb/testsuite/gdb.base/frame-unwind-disable.exp
>> new file mode 100644
>> index 00000000000..f4cad9a47fd
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.base/frame-unwind-disable.exp
>> @@ -0,0 +1,137 @@
>> +# Copyright 2024 Free Software Foundation, Inc.
> And again with the date.
>
>> +
>> +# This program is free software; you can redistribute it and/or modify
>> +# it under the terms of the GNU General Public License as published by
>> +# the Free Software Foundation; either version 3 of the License, or
>> +# (at your option) any later version.
>> +#
>> +# This program is distributed in the hope that it will be useful,
>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> +# GNU General Public License for more details.
>> +#
>> +# You should have received a copy of the GNU General Public License
>> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
>> +
>> +# Test multiple situations in which we may use the maintenance command to
>> +# disable and enable frame unwinders, and check that they really are
>> +# disabled when they say the are.
>> +
>> +standard_testfile .c
> You can drop '.c' here, it's the default.
>
>> +
>> +# Proc to check if the unwinder of the given name is in the desired state.
>> +# STATE can be either Y or N.
>> +proc check_unwinder_state { unwinder_name state {testname ""} } {
>> +    set should_pass false
>> +    set command "maint info frame-unwinders"
>> +    if {${testname} == ""} {
>> +	set testname "checking state ${state} for ${unwinder_name}"
>> +    }
>> +    gdb_test_multiple "${command}" "${testname}" -lbl {
>> +	-re "${unwinder_name}\\s+\\w+\\s+\\w+\\s+${state}\\s+(?=\r\n)" {
>> +	    set should_pass true
>> +	    exp_continue
>> +	}
>> +	-re "${command}" {
>> +	    exp_continue
>> +	}
>> +	-re "\\w+\\s+\\w+\\s+\\w+\\s+\\w+\\s+(?=\r\n)" {
>> +	    exp_continue
>> +	}
>> +	-re -wrap "" {
>> +	    gdb_assert ${should_pass} "${gdb_test_name}"
> I don't think the quotes around "${gdb_test_name}" are needed here?  In
> fact, there seem to be a few places where you place quotes around
> expansion of a single variable (e.g. "${command}" on the
> gdb_test_multiple line), I don't think any of these are needed.
>
> With these changes (and with or without the completion patch):

I applied all the changes, and I like the idea of adding completion, but 
I wonder: should we add a test for completion? If so, I think this is 
better saved for a later patch, so that we can work on a good test and 
further improve the completion, because it would be nice to also 
complete for "-class", "-name" and "-all", but I'm not sure how that'd 
work yet.

If a test isn't all that important we can add it now and do more work 
later on. I also have an inlined styling question

>
> Approved-By: Andrew Burgess <aburgess@redhat.com>
>
> Thanks,
> Andrew
>
>> +	}
>> +    }
>> +}
>> +
>> +# Check if all unwinders of class UNWINDER_CLASS are in the state STATE.
>> +# STATE can be either Y or N.
>> +# UNWINDER_CLASS can be one of: GDB, ARCH, EXTENSION, DEBUGINFO.  It can
>> +# also be \\w+ if checking all unwinders.
>> +proc check_unwinder_class { unwinder_class state {testname ""} } {
>> +    set command "maint info frame-unwinders"
>> +    set should_pass true
>> +    if {$testname == ""} {
>> +	set testname "checking if ${unwinder_class} state is ${state}"
>> +    }
>> +    gdb_test_multiple "${command}" "${testname}" -lbl {
>> +	-re "^\[^\r\n\]+\\s+\\w+\\s+${unwinder_class}\\s+\(\[YN\]\)\\s+(?=\r\n)" {
>> +	    # The unwinder name may have multiple words, so we need to use the
>> +	    # more generic [^\r\n] pattern to match the unwinders.
>> +	    set cur_state $expect_out(1,string)
>> +	    if {$cur_state == $state} {
>> +		set should_pass false
>> +	    }
>> +	    exp_continue
>> +	}
>> +	-re "${command}" {
>> +	    exp_continue
>> +	}
>> +	-re -wrap "" {
>> +	    gdb_assert ${should_pass} "${gdb_test_name}"
>> +	}
>> +    }
>> +}
>> +
>> +if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
>> +    return -1
>> +}
>> +
>> +if {![runto_main]} {
>> +    untested "couldn't run to main"
>> +    return
>> +}
>> +
>> +# Test disabling all unwinders.
>> +check_unwinder_class "\\w+" "Y" \
>> +    "all unwinders enabled before any changes"
>> +gdb_test_no_output "maint frame-unwinder disable -all"
>> +check_unwinder_class "\\w+" "N" \
>> +    "all unwinders were properly disabled"
>> +
>> +# Test if GDB can still make a backtrace once all unwinders are disabled.
>> +# It should be impossible.
>> +gdb_test "backtrace" \
>> +    ".*Required frame unwinder may have been disabled, see 'maint info frame-unwinders'.*" \
>> +    "no suitable unwinders should be found"
>> +
>> +# Reenable all unwinders.
>> +gdb_test_no_output "maint frame-unwinder enable -all"
>> +check_unwinder_class "\\w+" "Y" \
>> +    "all unwinders should be re-enabled"
>> +
>> +# Check that we are able to get backtraces once again.
>> +gdb_test "backtrace" ".0\\s+main .. at.*" \
>> +    "we can get usable backtraces again"
>> +
>> +# Check if we can disable an unwinder based on the name.
>> +check_unwinder_state "dummy" "Y"
>> +gdb_test_no_output "maint frame-unwinder disable -name dummy"
>> +check_unwinder_state "dummy" "N"
>> +# And verify what happens if you try to disable it again.
>> +gdb_test "maint frame-unwinder disable -name dummy" \
>> +    "unwinder dummy is already disabled" \
>> +    "disable already disabled unwinder"
>> +check_unwinder_state "dummy" "N" "dummy should continue disabled"
>> +
>> +foreach class {GDB ARCH DEBUGINFO EXTENSION} {
>> +    # Disable all unwinders of type CLASS, and check that the command worked.
>> +    gdb_test_no_output "maint frame-unwinder disable ${class}"
>> +    check_unwinder_class "${class}" "N"
>> +}
>> +
>> +# Now check if we are able to enable a single unwinder, and what happens if we
>> +# enable it twice.
>> +gdb_test_no_output "maint frame-unwinder enable -name dummy"
>> +check_unwinder_state "dummy" "Y" "successfully enabled dummy unwinder"
>> +gdb_test "maint frame-unwinder enable -name dummy" \
>> +    "unwinder dummy is already enabled" \
>> +    "enable already enabled unwinder"
>> +check_unwinder_state "dummy" "Y" "dummy should continue enabled"
>> +
>> +foreach class {GDB ARCH DEBUGINFO EXTENSION} {
>> +    # Enable all unwinders of type CLASS, and check that the command worked,
>> +    # using "-class" option to ensure it works.  Should make no difference.
>> +    gdb_test_no_output "maint frame-unwinder enable -class ${class}"
>> +    check_unwinder_class "${class}" "Y"
>> +}
>> diff --git a/gdb/testsuite/gdb.base/maint.exp b/gdb/testsuite/gdb.base/maint.exp
>> index 2c58ffa36c5..ae7ad0787e6 100644
>> --- a/gdb/testsuite/gdb.base/maint.exp
>> +++ b/gdb/testsuite/gdb.base/maint.exp
>> @@ -454,10 +454,6 @@ gdb_test_no_output "maint info line-table xxx.c" \
>>   
>>   set timeout $oldtimeout
>>   
>> -# Just check that the DWARF unwinders control flag is visible.
>> -gdb_test "maint show dwarf unwinders" \
>> -    "The DWARF stack unwinders are currently (on|off)\\."
>> -
>>   #============test help on maint commands
>>   
>>   test_prefix_command_help {"maint info" "maintenance info"} {
>> -- 
>> 2.47.0
> ---
>
> diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
> index 1417651108f..f3019b7ec18 100644
> --- a/gdb/frame-unwind.c
> +++ b/gdb/frame-unwind.c
> @@ -40,6 +40,7 @@ static const char * unwind_class_conversion[] =
>     "EXTENSION",
>     "DEBUGINFO",
>     "ARCH",
> +  nullptr
>   };
>   
>   /* Default sniffers, that must always be the first in the unwinder list,
> @@ -579,6 +580,29 @@ enable_disable_frame_unwinders (const char *args, int from_tty, bool enable)
>     reinit_frame_cache ();
>   }
>   
> +/* Completer for the "maint frame-unwinder enable|disable" commands.  */
> +
> +static void
> +enable_disable_frame_unwinders_completer (struct cmd_list_element *ignore,
> +					  completion_tracker &tracker,
> +					  const char *text,
> +					  const char */*word*/)
Would it be alright to write "const char * /*word*/" ? the */* is 
confusing my editor and it looks like malformed comments, and if I add 
the space, the red highlights go away.
  

Guinevere Larsen <guinevere@redhat.com> writes:

> On 1/16/25 9:06 AM, Andrew Burgess wrote:
>> Guinevere Larsen <guinevere@redhat.com> writes:
>>
>>> Sometimes, in the GDB testsuite, we want to test the ability of specific
>>> unwinders to handle some piece of code. Usually this is done by trying
>>> to outsmart GDB, or by coercing the compiler to remove information that
>>> GDB would rely on.  Both approaches have problems as GDB gets smarter
>>> with time, and that compilers might differ in version and behavior, or
>>> simply introduce new useful information. This was requested back in 2003
>>> in PR backtrace/8434.
>>>
>>> To improve our ability to thoroughly test GDB, this patch introduces a
>>> new maintenance command that allows a user to disable some unwinders,
>>> based on either the name of the unwinder or on its class. With this
>>> change, it will now be possible for GDB to not find any frame unwinders
>>> for a given frame, which would previously cause GDB to assert. GDB will
>>> now check if any frame unwinder has been disabled, and if some has, it
>>> will just error out instead of asserting.
>>>
>>> Unwinders can be disabled or re-enabled in 3 different ways:
>>> * Disabling/enabling all at once (using '-all').
>>> * By specifying an unwinder class to be disabled (option '-class').
>>> * By specifying the name of an unwinder (option '-name').
>>>
>>> If you give no options to the command, GDB assumes the input is an
>>> unwinder class. '-class' would make no difference if used, is just here
>>> for completeness.
>>>
>>> This command is meant to be used once the inferior is already at the
>>> desired location for the test. An example session would be:
>>>
>>> (gdb) start
>>> Temporary breakpoint 1, main () at omp.c:17
>>> 17          func();
>>> (gdb) maint frame-unwinder disable ARCH
>>> (gdb) bt
>>> \#0  main () at omp.c:17
>>> (gdb) maint frame-unwinder enable ARCH
>>> (gdb) cont
>>> Continuing.
>>>
>>> This commit is a more generic version of commit 3c3bb0580be0,
>>> and so, based on the final paragraph of the commit message:
>>>      gdb: Add switch to disable DWARF stack unwinders
>>> <...>
>>>      If in the future we find ourselves adding more switches to disable
>>>      different unwinders, then we should probably move to a more generic
>>>      solution, and remove this patch.
>>> this patch also reverts 3c3bb0580be0
>>>
>>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=8434
>>> Reviewed-By: Eli Zaretskii <eliz@gnu.org>
>>> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
>>> ---
>>>   gdb/NEWS                                      |  17 ++
>>>   gdb/doc/gdb.texinfo                           |  49 ++--
>>>   gdb/dwarf2/frame-tailcall.c                   |   3 -
>>>   gdb/dwarf2/frame.c                            |  30 ---
>>>   gdb/dwarf2/frame.h                            |   6 -
>>>   gdb/frame-unwind.c                            | 237 +++++++++++++++++-
>>>   gdb/frame-unwind.h                            |   9 +
>>>   .../gdb.base/frame-info-consistent.exp        |   8 +-
>>>   gdb/testsuite/gdb.base/frame-unwind-disable.c |  22 ++
>>>   .../gdb.base/frame-unwind-disable.exp         | 137 ++++++++++
>>>   gdb/testsuite/gdb.base/maint.exp              |   4 -
>>>   11 files changed, 437 insertions(+), 85 deletions(-)
>>>   create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.c
>>>   create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.exp
>>>
>>> diff --git a/gdb/NEWS b/gdb/NEWS
>>> index 245b355669a..ef3317c11cb 100644
>>> --- a/gdb/NEWS
>>> +++ b/gdb/NEWS
>>> @@ -125,6 +125,13 @@ maintenance info blocks [ADDRESS]
>>>     are listed starting at the inner global block out to the most inner
>>>     block.
>>>   
>>> +maintenance frame-unwinder disable [-all | -name NAME | [-class] CLASS]
>>> +maintenance frame-unwinder enable [-all | -name NAME | [-class] CLASS]
>>> +  Enable or disable frame unwinders.  This is only meant to be used when
>>> +  testing unwinders themselves, and you want to ensure that a fallback
>>> +  algorithm won't obscure a regression.  GDB is not expected to behave
>>> +  well if you try to execute the inferior with unwinders disabled.
>>> +
>>>   info missing-objfile-handlers
>>>     List all the registered missing-objfile handlers.
>>>   
>>> @@ -167,6 +174,16 @@ maintenance print remote-registers
>>>   mainenance info frame-unwinders
>>>     Add a CLASS column to the output.  This class is a somewhat arbitrary
>>>     grouping of unwinders, based on which area of GDB adds the unwinder.
>>> +  Also add an ENABLED column, that will show if the unwinder is enabled
>>> +  or not.
>>> +
>>> +maintenance set dwarf unwinders (on|off)
>>> +  This command has been removed because the same functionality can be
>>> +  achieved with maint frame-unwinder (enable|disable) DEBUGINFO.
>>> +
>>> +maintenance show dwarf unwinders
>>> +  This command has been removed since the functionality can be achieved
>>> +  by checking the last column of maint info frame-unwinders.
>>>   
>>>   show configuration
>>>     Now includes the version of GNU Readline library that GDB is using.
>>> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
>>> index 115c1f46b7f..10e6654a03b 100644
>>> --- a/gdb/doc/gdb.texinfo
>>> +++ b/gdb/doc/gdb.texinfo
>>> @@ -42210,31 +42210,6 @@ On hosts without threading, or where worker threads have been disabled
>>>   at runtime, this setting has no effect, as DWARF reading is always
>>>   done on the main thread, and is therefore always synchronous.
>>>   
>>> -@kindex maint set dwarf unwinders
>>> -@kindex maint show dwarf unwinders
>>> -@item maint set dwarf unwinders
>>> -@itemx maint show dwarf unwinders
>>> -Control use of the DWARF frame unwinders.
>>> -
>>> -@cindex DWARF frame unwinders
>>> -Many targets that support DWARF debugging use @value{GDBN}'s DWARF
>>> -frame unwinders to build the backtrace.  Many of these targets will
>>> -also have a second mechanism for building the backtrace for use in
>>> -cases where DWARF information is not available, this second mechanism
>>> -is often an analysis of a function's prologue.
>>> -
>>> -In order to extend testing coverage of the second level stack
>>> -unwinding mechanisms it is helpful to be able to disable the DWARF
>>> -stack unwinders, this can be done with this switch.
>>> -
>>> -In normal use of @value{GDBN} disabling the DWARF unwinders is not
>>> -advisable, there are cases that are better handled through DWARF than
>>> -prologue analysis, and the debug experience is likely to be better
>>> -with the DWARF frame unwinders enabled.
>>> -
>>> -If DWARF frame unwinders are not supported for a particular target
>>> -architecture, then enabling this flag does not cause them to be used.
>>> -
>>>   @kindex maint info frame-unwinders
>>>   @item maint info frame-unwinders
>>>   List the frame unwinders currently in effect, starting with the highest
>>> @@ -42252,6 +42227,30 @@ Unwinders installed by debug information readers.
>>>   Unwinders installed by the architecture specific code.
>>>   @end table
>>>   
>>> +@kindex maint frame-unwinder disable
>>> +@kindex maint frame-unwinder enable
>>> +@item maint frame-unwinder disable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
>>> +@item maint frame-unwinder enable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
>>> +Disable or enable frame unwinders.  This is meant only as a testing tool, and
>>> +@value{GDBN} is not guaranteed to work properly if it is unable to find
>>> +valid frame unwinders.
>>> +
>>> +The meaning of each of the invocations are as follows:
>>> +
>>> +@table @samp
>>> +@item @code{-all}
>>> +Disable or enable all unwinders.
>>> +@item @code{-name} @var{name}
>>> +@var{name} is the exact name of the unwinder to be disabled or enabled.
>>> +@item [@code{-class}] @var{class}
>>> +@var{class} is the class of frame unwinders to be disabled or enabled.
>>> +The class may include the prefix @code{FRAME_UNWINDER_}, but it is not
>>> +required.
>>> +@end table
>>> +
>>> +@var{name} and @var{class} are always case insensitive.  If no option
>>> +starting wth @code{-} is given, @value{GDBN} assumes @code{-class}.
>>> +
>>>   @kindex maint set worker-threads
>>>   @kindex maint show worker-threads
>>>   @item maint set worker-threads
>>> diff --git a/gdb/dwarf2/frame-tailcall.c b/gdb/dwarf2/frame-tailcall.c
>>> index 54813d00b03..2d7ab740f62 100644
>>> --- a/gdb/dwarf2/frame-tailcall.c
>>> +++ b/gdb/dwarf2/frame-tailcall.c
>>> @@ -321,9 +321,6 @@ tailcall_frame_sniffer (const struct frame_unwind *self,
>>>     int next_levels;
>>>     struct tailcall_cache *cache;
>>>   
>>> -  if (!dwarf2_frame_unwinders_enabled_p)
>>> -    return 0;
>>> -
>>>     /* Inner tail call element does not make sense for a sentinel frame.  */
>>>     next_frame = get_next_frame (this_frame);
>>>     if (next_frame == NULL)
>>> diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
>>> index 85e1d59bc09..e0e8eb5dbec 100644
>>> --- a/gdb/dwarf2/frame.c
>>> +++ b/gdb/dwarf2/frame.c
>>> @@ -183,9 +183,6 @@ static ULONGEST read_encoded_value (struct comp_unit *unit, gdb_byte encoding,
>>>   				    unrelocated_addr func_base);
>>>   
>>>   
>>> -/* See dwarf2/frame.h.  */
>>> -bool dwarf2_frame_unwinders_enabled_p = true;
>>> -
>>>   /* Store the length the expression for the CFA in the `cfa_reg' field,
>>>      which is unused in that case.  */
>>>   #define cfa_exp_len cfa_reg
>>> @@ -1306,9 +1303,6 @@ static int
>>>   dwarf2_frame_sniffer (const struct frame_unwind *self,
>>>   		      const frame_info_ptr &this_frame, void **this_cache)
>>>   {
>>> -  if (!dwarf2_frame_unwinders_enabled_p)
>>> -    return 0;
>>> -
>>>     /* Grab an address that is guaranteed to reside somewhere within the
>>>        function.  get_frame_pc(), with a no-return next function, can
>>>        end up returning something past the end of this function's body.
>>> @@ -2253,34 +2247,10 @@ dwarf2_build_frame_info (struct objfile *objfile)
>>>     set_comp_unit (objfile, unit.release ());
>>>   }
>>>   
>>> -/* Handle 'maintenance show dwarf unwinders'.  */
>>> -
>>> -static void
>>> -show_dwarf_unwinders_enabled_p (struct ui_file *file, int from_tty,
>>> -				struct cmd_list_element *c,
>>> -				const char *value)
>>> -{
>>> -  gdb_printf (file,
>>> -	      _("The DWARF stack unwinders are currently %s.\n"),
>>> -	      value);
>>> -}
>>> -
>>>   void _initialize_dwarf2_frame ();
>>>   void
>>>   _initialize_dwarf2_frame ()
>>>   {
>>> -  add_setshow_boolean_cmd ("unwinders", class_obscure,
>>> -			   &dwarf2_frame_unwinders_enabled_p , _("\
>>> -Set whether the DWARF stack frame unwinders are used."), _("\
>>> -Show whether the DWARF stack frame unwinders are used."), _("\
>>> -When enabled the DWARF stack frame unwinders can be used for architectures\n\
>>> -that support the DWARF unwinders.  Enabling the DWARF unwinders for an\n\
>>> -architecture that doesn't support them will have no effect."),
>>> -			   NULL,
>>> -			   show_dwarf_unwinders_enabled_p,
>>> -			   &set_dwarf_cmdlist,
>>> -			   &show_dwarf_cmdlist);
>>> -
>>>   #if GDB_SELF_TEST
>>>     selftests::register_test_foreach_arch ("execute_cfa_program",
>>>   					 selftests::execute_cfa_program_test);
>>> diff --git a/gdb/dwarf2/frame.h b/gdb/dwarf2/frame.h
>>> index 2167310fbdf..fe2d669a983 100644
>>> --- a/gdb/dwarf2/frame.h
>>> +++ b/gdb/dwarf2/frame.h
>>> @@ -198,12 +198,6 @@ struct dwarf2_frame_state
>>>     bool armcc_cfa_offsets_reversed = false;
>>>   };
>>>   
>>> -/* When this is true the DWARF frame unwinders can be used if they are
>>> -   registered with the gdbarch.  Not all architectures can or do use the
>>> -   DWARF unwinders.  Setting this to true on a target that does not
>>> -   otherwise support the DWARF unwinders has no effect.  */
>>> -extern bool dwarf2_frame_unwinders_enabled_p;
>>> -
>>>   /* Set the architecture-specific register state initialization
>>>      function for GDBARCH to INIT_REG.  */
>>>   
>>> diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
>>> index 3ab6af1c4da..968bb846402 100644
>>> --- a/gdb/frame-unwind.c
>>> +++ b/gdb/frame-unwind.c
>>> @@ -29,6 +29,7 @@
>>>   #include "gdbarch.h"
>>>   #include "dwarf2/frame-tailcall.h"
>>>   #include "cli/cli-cmds.h"
>>> +#include "cli/cli-option.h"
>>>   #include "inferior.h"
>>>   
>>>   /* Conversion list between the enum for frame_unwind_class and
>>> @@ -89,6 +90,20 @@ frame_unwinder_class_str (frame_unwind_class uclass)
>>>     return unwind_class_conversion[uclass];
>>>   }
>>>   
>>> +/* Case insensitive search for a frame_unwind_class based on the given
>>> +   string.  */
>>> +static enum frame_unwind_class
>>> +str_to_frame_unwind_class (const char *class_str)
>>> +{
>>> +  for (int i = 0; i < UNWIND_CLASS_NUMBER; i++)
>>> +    {
>>> +      if (strcasecmp (unwind_class_conversion[i], class_str) == 0)
>>> +	return (frame_unwind_class) i;
>>> +    }
>>> +
>>> +  error (_("Unknown frame unwind class: %s"), class_str);
>>> +}
>>> +
>>>   void
>>>   frame_unwind_prepend_unwinder (struct gdbarch *gdbarch,
>>>   				const struct frame_unwind *unwinder)
>>> @@ -175,27 +190,46 @@ frame_unwind_find_by_frame (const frame_info_ptr &this_frame, void **this_cache)
>>>     FRAME_SCOPED_DEBUG_ENTER_EXIT;
>>>     frame_debug_printf ("this_frame=%d", frame_relative_level (this_frame));
>>>   
>>> -  const struct frame_unwind *unwinder_from_target;
>>> +  /* If we see a disabled unwinder, we assume some test is being run on
>>> +     GDB, and we don't want to internal_error at the end of this function.  */
>>> +  bool seen_disabled_unwinder = false;
>>> +  /* Lambda to factor out the logic of checking if an unwinder is enabled,
>>> +     testing it and otherwise recording if we saw a disable unwinder.  */
>>> +  auto test_unwinder = [&] (const struct frame_unwind *unwinder)
>>> +    {
>>> +      if (unwinder == nullptr)
>>> +	return false;
>>> +
>>> +      if (!unwinder->enabled ())
>>> +	{
>>> +	  seen_disabled_unwinder = true;
>>> +	  return false;
>>> +	}
>>> +
>>> +      return frame_unwind_try_unwinder (this_frame,
>>> +					this_cache,
>>> +					unwinder);
>>> +    };
>>>   
>>> -  unwinder_from_target = target_get_unwinder ();
>>> -  if (unwinder_from_target != NULL
>>> -      && frame_unwind_try_unwinder (this_frame, this_cache,
>>> -				   unwinder_from_target))
>>> +  if (test_unwinder (target_get_unwinder ()))
>>>       return;
>>>   
>>> -  unwinder_from_target = target_get_tailcall_unwinder ();
>>> -  if (unwinder_from_target != NULL
>>> -      && frame_unwind_try_unwinder (this_frame, this_cache,
>>> -				   unwinder_from_target))
>>> +  if (test_unwinder (target_get_tailcall_unwinder ()))
>>>       return;
>>>   
>>>     struct gdbarch *gdbarch = get_frame_arch (this_frame);
>>>     std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>>>     for (auto unwinder : *table)
>>> -    if (frame_unwind_try_unwinder (this_frame, this_cache, unwinder))
>>> -      return;
>>> +    {
>>> +      if (test_unwinder (unwinder))
>>> +	return;
>>> +    }
>>>   
>>> -  internal_error (_("frame_unwind_find_by_frame failed"));
>>> +  if (seen_disabled_unwinder)
>>> +    error (_("Required frame unwinder may have been disabled"
>>> +	     ", see 'maint info frame-unwinders'"));
>>> +  else
>>> +    internal_error (_("frame_unwind_find_by_frame failed"));
>>>   }
>>>   
>>>   /* A default frame sniffer which always accepts the frame.  Used by
>>> @@ -394,10 +428,11 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>>>     std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>>>   
>>>     ui_out *uiout = current_uiout;
>>> -  ui_out_emit_table table_emitter (uiout, 3, -1, "FrameUnwinders");
>>> +  ui_out_emit_table table_emitter (uiout, 4, -1, "FrameUnwinders");
>>>     uiout->table_header (27, ui_left, "name", "Name");
>>>     uiout->table_header (25, ui_left, "type", "Type");
>>>     uiout->table_header (9, ui_left, "class", "Class");
>>> +  uiout->table_header (8, ui_left, "enabled", "Enabled");
>>>     uiout->table_body ();
>>>   
>>>     for (auto unwinder : *table)
>>> @@ -407,10 +442,145 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>>>         uiout->field_string ("type", frame_type_str (unwinder->type ()));
>>>         uiout->field_string ("class", frame_unwinder_class_str (
>>>   					unwinder->unwinder_class ()));
>>> +      uiout->field_string ("enabled", unwinder->enabled () ? "Y" : "N");
>>>         uiout->text ("\n");
>>>       }
>>>   }
>>>   
>>> +/* Options for disabling frame unwinders.  */
>>> +struct maint_frame_unwind_options
>>> +{
>>> +  std::string unwinder_name;
>>> +  const char *unwinder_class = nullptr;
>>> +  bool all = false;
>>> +};
>>> +
>>> +static const gdb::option::option_def maint_frame_unwind_opt_defs[] = {
>>> +
>>> +  gdb::option::flag_option_def<maint_frame_unwind_options> {
>>> +    "all",
>>> +    [] (maint_frame_unwind_options *opt) { return &opt->all; },
>>> +    nullptr,
>>> +    N_("Change the state of all unwinders")
>>> +  },
>>> +  gdb::option::string_option_def<maint_frame_unwind_options> {
>>> +    "name",
>>> +    [] (maint_frame_unwind_options *opt) { return &opt->unwinder_name; },
>>> +    nullptr,
>>> +    N_("The name of the unwinder to have its state changed")
>>> +  },
>>> +  gdb::option::enum_option_def<maint_frame_unwind_options> {
>>> +    "class",
>>> +    unwind_class_conversion,
>>> +    [] (maint_frame_unwind_options *opt) { return &opt->unwinder_class; },
>>> +    nullptr,
>>> +    N_("The class of unwinders to have their states changed")
>>> +  }
>>> +};
>>> +
>>> +static inline gdb::option::option_def_group
>>> +make_frame_unwind_enable_disable_options (maint_frame_unwind_options *opts)
>>> +{
>>> +  return {{maint_frame_unwind_opt_defs}, opts};
>>> +}
>>> +
>>> +/* Helper function to both enable and disable frame unwinders.
>>> +   If ENABLE is true, this call will be enabling unwinders,
>>> +   otherwise the unwinders will be disabled.  */
>>> +static void
>>> +enable_disable_frame_unwinders (const char *args, int from_tty, bool enable)
>>> +{
>>> +  if (args == nullptr)
>>> +    {
>>> +      if (enable)
>>> +	error (_("Specify which frame unwinder(s) should be enabled"));
>>> +      else
>>> +	error (_("Specify which frame unwinder(s) should be disabled"));
>>> +    }
>>> +
>>> +  struct gdbarch* gdbarch = current_inferior ()->arch ();
>>> +  std::vector<const frame_unwind *> *unwinder_list
>>> +    = get_frame_unwind_table (gdbarch);
>>> +
>>> +  maint_frame_unwind_options opts;
>>> +  gdb::option::process_options
>>> +    (&args, gdb::option::PROCESS_OPTIONS_UNKNOWN_IS_ERROR,
>>> +     make_frame_unwind_enable_disable_options (&opts));
>>> +
>>> +  if ((opts.all && !opts.unwinder_name.empty ())
>>> +      || (opts.all && opts.unwinder_class != nullptr)
>>> +      || (!opts.unwinder_name.empty () && opts.unwinder_class != nullptr))
>>> +    error (_("Options are mutually exclusive"));
>>> +
>>> +  /* First see if the user wants to change all unwinders.  */
>>> +  if (opts.all)
>>> +    {
>>> +      for (const frame_unwind *u : *unwinder_list)
>>> +	u->set_enabled (enable);
>>> +
>>> +      reinit_frame_cache ();
>>> +      return;
>>> +    }
>>> +
>>> +  /* If user entered a specific unwinder name, handle it here.  If the
>>> +     unwinder is already at the expected state, error out.  */
>>> +  if (!opts.unwinder_name.empty ())
>>> +    {
>>> +      bool did_something = false;
>>> +      for (const frame_unwind *unwinder : *unwinder_list)
>>> +	{
>>> +	  if (strcasecmp (unwinder->name (),
>>> +			  opts.unwinder_name.c_str ()) == 0)
>>> +	    {
>>> +	      if (unwinder->enabled () == enable)
>>> +		{
>>> +		  if (unwinder->enabled ())
>>> +		    error (_("unwinder %s is already enabled"),
>>> +			     unwinder->name ());
>>> +		  else
>>> +		    error (_("unwinder %s is already disabled"),
>>> +			     unwinder->name ());
>>> +		}
>>> +	      unwinder->set_enabled (enable);
>>> +
>>> +	      did_something = true;
>>> +	      break;
>>> +	    }
>>> +	}
>>> +      if (!did_something)
>>> +	error (_("couldn't find unwinder named %s"),
>>> +	       opts.unwinder_name.c_str ());
>>> +    }
>>> +  else
>>> +    {
>>> +      if (opts.unwinder_class == nullptr)
>>> +	opts.unwinder_class = args;
>>> +      enum frame_unwind_class dclass = str_to_frame_unwind_class
>>> +	(opts.unwinder_class);
>>> +      for (auto unwinder: *unwinder_list)
>> I think you should stick with the form you use earlier:
>>
>>    (const frame_unwind *unwinder : *unwinder_list)
>>
>> But if you really want to stick with auto, then I think:
>>
>>   (const auto &unwinder : *unwinder_list)
>>
>> would be OK.
>>
>>
>>> +	{
>>> +	  if (unwinder->unwinder_class () == dclass)
>>> +	    unwinder->set_enabled (enable);
>>> +	}
>>> +    }
>>> +
>>> +  reinit_frame_cache ();
>>> +}
>>> +
>>> +/* Implement "maint frame-unwinder disable" command.  */
>>> +static void
>>> +maintenance_disable_frame_unwinders (const char *args, int from_tty)
>>> +{
>>> +  enable_disable_frame_unwinders (args, from_tty, false);
>>> +}
>>> +
>>> +/* Implement "maint frame-unwinder enable" command.  */
>>> +static void
>>> +maintenance_enable_frame_unwinders (const char *args, int from_tty)
>>> +{
>>> +  enable_disable_frame_unwinders (args, from_tty, true);
>>> +}
>>> +
>>>   void _initialize_frame_unwind ();
>>>   void
>>>   _initialize_frame_unwind ()
>>> @@ -423,4 +593,45 @@ _initialize_frame_unwind ()
>>>   List the frame unwinders currently in effect.\n\
>>>   Unwinders are listed starting with the highest priority."),
>>>   	   &maintenanceinfolist);
>>> +
>>> +  /* Add "maint frame-unwinder disable/enable".  */
>>> +  static struct cmd_list_element *maint_frame_unwinder;
>>> +
>>> +  add_basic_prefix_cmd ("frame-unwinder", class_maintenance,
>>> +			_("Commands handling frame unwinders."),
>>> +			&maint_frame_unwinder, 0, &maintenancelist);
>>> +
>>> +  add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
>>> +	   _("\
>>> +Disable one or more frame unwinder(s).\n\
>>> +Usage: maint frame-unwinder disable [-all | -name NAME | [-class] CLASS]\n\
>>> +\n\
>>> +These are the meanings of the options:\n\
>>> +\t-all    - All available unwinders will be disabled\n\
>>> +\t-name   - NAME is the exact name of the frame unwinder to be disabled\n\
>>> +\t-class  - CLASS is the class of unwinders to be disabled. Valid classes are:\n\
>>> +\t\tGDB       - Unwinders added by GDB core;\n\
>>> +\t\tEXTENSION - Unwinders added by extension languages;\n\
>>> +\t\tDEBUGINFO - Unwinders that handle debug information;\n\
>>> +\t\tARCH      - Unwinders that use architecture-specific information;\n\
>>> +\n\
>>> +UNWINDER and NAME are case insensitive."),
>>> +	   &maint_frame_unwinder);
>>> +
>>> +  add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
>>> +	   _("\
>>> +Enable one or more frame unwinder(s).\n\
>>> +Usage: maint frame-unwinder enable [-all | -name NAME | [-class] CLASS]\n\
>>> +\n\
>>> +These are the meanings of the options:\n\
>>> +\t-all    - All available unwinders will be enabled\n\
>>> +\t-name   - NAME is the exact name of the frame unwinder to be enabled\n\
>>> +\t-class  - CLASS is the class of unwinders to be enabled. Valid classes are:\n\
>>> +\t\tGDB       - Unwinders added by GDB core;\n\
>>> +\t\tEXTENSION - Unwinders added by extension languages;\n\
>>> +\t\tDEBUGINFO - Unwinders that handle debug information;\n\
>>> +\t\tARCH      - Unwinders that use architecture-specific information;\n\
>>> +\n\
>>> +UNWINDER and NAME are case insensitive."),
>>> +	   &maint_frame_unwinder);
>>>   }
>> At the bottom of this email you'll find a small patch which applies on
>> top of this and adds some basic command completion.  It doesn't complete
>> the NAMEs, I'm not sure if there's a good way to do that (yet).  It also
>> doesn't switch the help text to use the %OPTIONS% mechanism, I tried
>> that, but I think there may be some bugs with the formatting (I'll look
>> into it), so I've left that off.
>>
>> You don't have to, we can add completion later, but I do think it would
>> be good to merge the patch below with this one.  But it is up to you.
>> Take a look and see what you think.
>>
>>> diff --git a/gdb/frame-unwind.h b/gdb/frame-unwind.h
>>> index 13f18618d24..adf8b47982c 100644
>>> --- a/gdb/frame-unwind.h
>>> +++ b/gdb/frame-unwind.h
>>> @@ -192,6 +192,12 @@ class frame_unwind
>>>     const frame_data *unwind_data () const
>>>     { return m_unwind_data; }
>>>   
>>> +  bool enabled () const
>>> +  { return m_enabled; }
>>> +
>>> +  void set_enabled (bool state) const
>>> +  { m_enabled = state; }
>>> +
>>>     /* Default stop_reason implementation.  It reports NO_REASON, unless the
>>>        frame is the outermost.  */
>>>   
>>> @@ -245,6 +251,9 @@ class frame_unwind
>>>     frame_unwind_class m_unwinder_class;
>>>   
>>>     const frame_data *m_unwind_data;
>>> +
>>> +  /* Whether this unwinder can be used when sniffing.  */
>>> +  mutable bool m_enabled = true;
>>>   };
>>>   
>>>   /* This is a legacy version of the frame unwinder.  The original struct
>>> diff --git a/gdb/testsuite/gdb.base/frame-info-consistent.exp b/gdb/testsuite/gdb.base/frame-info-consistent.exp
>>> index fe0cfad95bc..4f483111a91 100644
>>> --- a/gdb/testsuite/gdb.base/frame-info-consistent.exp
>>> +++ b/gdb/testsuite/gdb.base/frame-info-consistent.exp
>>> @@ -95,11 +95,11 @@ proc compare_frames {frames} {
>>>       }
>>>   }
>>>   
>>> -proc test {dwarf_unwinder} {
>>> +proc test {enable} {
>>>   
>>>       clean_restart $::binfile
>>>   
>>> -    gdb_test_no_output "maint set dwarf unwinder $dwarf_unwinder"
>>> +    gdb_test_no_output "maint frame-unwinder $enable DEBUGINFO"
>>>   
>>>       if {![runto_main]} {
>>>   	return 0
>>> @@ -134,6 +134,6 @@ proc test {dwarf_unwinder} {
>>>       }
>>>   }
>>>   
>>> -foreach_with_prefix dwarf {"off" "on"} {
>>> -    test $dwarf
>>> +foreach_with_prefix action {"disable" "enable"} {
>>> +    test $action
>>>   }
>>> diff --git a/gdb/testsuite/gdb.base/frame-unwind-disable.c b/gdb/testsuite/gdb.base/frame-unwind-disable.c
>>> new file mode 100644
>>> index 00000000000..bbcfb01316e
>>> --- /dev/null
>>> +++ b/gdb/testsuite/gdb.base/frame-unwind-disable.c
>>> @@ -0,0 +1,22 @@
>>> +/* This testcase is part of GDB, the GNU debugger.
>>> +
>>> +   Copyright 2024 Free Software Foundation, Inc.
>> Remember to update the copyright date when rebasing.
>>
>>> +
>>> +   This program is free software; you can redistribute it and/or modify
>>> +   it under the terms of the GNU General Public License as published by
>>> +   the Free Software Foundation; either version 3 of the License, or
>>> +   (at your option) any later version.
>>> +
>>> +   This program is distributed in the hope that it will be useful,
>>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> +   GNU General Public License for more details.
>>> +
>>> +   You should have received a copy of the GNU General Public License
>>> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
>>> +
>>> +int
>>> +main ()
>>> +{
>>> +  return 0;
>>> +}
>>> diff --git a/gdb/testsuite/gdb.base/frame-unwind-disable.exp b/gdb/testsuite/gdb.base/frame-unwind-disable.exp
>>> new file mode 100644
>>> index 00000000000..f4cad9a47fd
>>> --- /dev/null
>>> +++ b/gdb/testsuite/gdb.base/frame-unwind-disable.exp
>>> @@ -0,0 +1,137 @@
>>> +# Copyright 2024 Free Software Foundation, Inc.
>> And again with the date.
>>
>>> +
>>> +# This program is free software; you can redistribute it and/or modify
>>> +# it under the terms of the GNU General Public License as published by
>>> +# the Free Software Foundation; either version 3 of the License, or
>>> +# (at your option) any later version.
>>> +#
>>> +# This program is distributed in the hope that it will be useful,
>>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> +# GNU General Public License for more details.
>>> +#
>>> +# You should have received a copy of the GNU General Public License
>>> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
>>> +
>>> +# Test multiple situations in which we may use the maintenance command to
>>> +# disable and enable frame unwinders, and check that they really are
>>> +# disabled when they say the are.
>>> +
>>> +standard_testfile .c
>> You can drop '.c' here, it's the default.
>>
>>> +
>>> +# Proc to check if the unwinder of the given name is in the desired state.
>>> +# STATE can be either Y or N.
>>> +proc check_unwinder_state { unwinder_name state {testname ""} } {
>>> +    set should_pass false
>>> +    set command "maint info frame-unwinders"
>>> +    if {${testname} == ""} {
>>> +	set testname "checking state ${state} for ${unwinder_name}"
>>> +    }
>>> +    gdb_test_multiple "${command}" "${testname}" -lbl {
>>> +	-re "${unwinder_name}\\s+\\w+\\s+\\w+\\s+${state}\\s+(?=\r\n)" {
>>> +	    set should_pass true
>>> +	    exp_continue
>>> +	}
>>> +	-re "${command}" {
>>> +	    exp_continue
>>> +	}
>>> +	-re "\\w+\\s+\\w+\\s+\\w+\\s+\\w+\\s+(?=\r\n)" {
>>> +	    exp_continue
>>> +	}
>>> +	-re -wrap "" {
>>> +	    gdb_assert ${should_pass} "${gdb_test_name}"
>> I don't think the quotes around "${gdb_test_name}" are needed here?  In
>> fact, there seem to be a few places where you place quotes around
>> expansion of a single variable (e.g. "${command}" on the
>> gdb_test_multiple line), I don't think any of these are needed.
>>
>> With these changes (and with or without the completion patch):
>
> I applied all the changes, and I like the idea of adding completion, but 
> I wonder: should we add a test for completion? If so, I think this is 
> better saved for a later patch, so that we can work on a good test and 
> further improve the completion, because it would be nice to also 
> complete for "-class", "-name" and "-all", but I'm not sure how that'd 
> work yet.
>
> If a test isn't all that important we can add it now and do more work 
> later on. I also have an inlined styling question

I'm not sure every function with completion has tests.  We do have some
general tests that cover completion though.

If it bothers you, then feel free to leave it out for now, I certainly
don't want to delay this work going in just for completion of a
maintenance command, you already switched over to the option system for
me, which means we're better placed to add completion now or later, so
I'm grateful for that.

The function I proposed should be able to complete the '-class',
'-name', and '-all' option names.  Additionally, the '-class' value
should complete.  And the class name as an operand, if there are no
options given.

Completion of -name values is trickier, as the possible set of names can
change by architecture, and the set of extensions loaded (I think).
What we really need is for -name to be a "dynamic" enum option, where
the dynamic property is provided by a callback which gets the list of
possible enum values.  But such dynamic enums don't currently exist.
But I might look into adding that feature once this patch lands.

Anyway, feel free to add the completion, or not.  If not I'll follow up
afterwards.

>
>>
>> Approved-By: Andrew Burgess <aburgess@redhat.com>
>>
>> Thanks,
>> Andrew
>>
>>> +	}
>>> +    }
>>> +}
>>> +
>>> +# Check if all unwinders of class UNWINDER_CLASS are in the state STATE.
>>> +# STATE can be either Y or N.
>>> +# UNWINDER_CLASS can be one of: GDB, ARCH, EXTENSION, DEBUGINFO.  It can
>>> +# also be \\w+ if checking all unwinders.
>>> +proc check_unwinder_class { unwinder_class state {testname ""} } {
>>> +    set command "maint info frame-unwinders"
>>> +    set should_pass true
>>> +    if {$testname == ""} {
>>> +	set testname "checking if ${unwinder_class} state is ${state}"
>>> +    }
>>> +    gdb_test_multiple "${command}" "${testname}" -lbl {
>>> +	-re "^\[^\r\n\]+\\s+\\w+\\s+${unwinder_class}\\s+\(\[YN\]\)\\s+(?=\r\n)" {
>>> +	    # The unwinder name may have multiple words, so we need to use the
>>> +	    # more generic [^\r\n] pattern to match the unwinders.
>>> +	    set cur_state $expect_out(1,string)
>>> +	    if {$cur_state == $state} {
>>> +		set should_pass false
>>> +	    }
>>> +	    exp_continue
>>> +	}
>>> +	-re "${command}" {
>>> +	    exp_continue
>>> +	}
>>> +	-re -wrap "" {
>>> +	    gdb_assert ${should_pass} "${gdb_test_name}"
>>> +	}
>>> +    }
>>> +}
>>> +
>>> +if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
>>> +    return -1
>>> +}
>>> +
>>> +if {![runto_main]} {
>>> +    untested "couldn't run to main"
>>> +    return
>>> +}
>>> +
>>> +# Test disabling all unwinders.
>>> +check_unwinder_class "\\w+" "Y" \
>>> +    "all unwinders enabled before any changes"
>>> +gdb_test_no_output "maint frame-unwinder disable -all"
>>> +check_unwinder_class "\\w+" "N" \
>>> +    "all unwinders were properly disabled"
>>> +
>>> +# Test if GDB can still make a backtrace once all unwinders are disabled.
>>> +# It should be impossible.
>>> +gdb_test "backtrace" \
>>> +    ".*Required frame unwinder may have been disabled, see 'maint info frame-unwinders'.*" \
>>> +    "no suitable unwinders should be found"
>>> +
>>> +# Reenable all unwinders.
>>> +gdb_test_no_output "maint frame-unwinder enable -all"
>>> +check_unwinder_class "\\w+" "Y" \
>>> +    "all unwinders should be re-enabled"
>>> +
>>> +# Check that we are able to get backtraces once again.
>>> +gdb_test "backtrace" ".0\\s+main .. at.*" \
>>> +    "we can get usable backtraces again"
>>> +
>>> +# Check if we can disable an unwinder based on the name.
>>> +check_unwinder_state "dummy" "Y"
>>> +gdb_test_no_output "maint frame-unwinder disable -name dummy"
>>> +check_unwinder_state "dummy" "N"
>>> +# And verify what happens if you try to disable it again.
>>> +gdb_test "maint frame-unwinder disable -name dummy" \
>>> +    "unwinder dummy is already disabled" \
>>> +    "disable already disabled unwinder"
>>> +check_unwinder_state "dummy" "N" "dummy should continue disabled"
>>> +
>>> +foreach class {GDB ARCH DEBUGINFO EXTENSION} {
>>> +    # Disable all unwinders of type CLASS, and check that the command worked.
>>> +    gdb_test_no_output "maint frame-unwinder disable ${class}"
>>> +    check_unwinder_class "${class}" "N"
>>> +}
>>> +
>>> +# Now check if we are able to enable a single unwinder, and what happens if we
>>> +# enable it twice.
>>> +gdb_test_no_output "maint frame-unwinder enable -name dummy"
>>> +check_unwinder_state "dummy" "Y" "successfully enabled dummy unwinder"
>>> +gdb_test "maint frame-unwinder enable -name dummy" \
>>> +    "unwinder dummy is already enabled" \
>>> +    "enable already enabled unwinder"
>>> +check_unwinder_state "dummy" "Y" "dummy should continue enabled"
>>> +
>>> +foreach class {GDB ARCH DEBUGINFO EXTENSION} {
>>> +    # Enable all unwinders of type CLASS, and check that the command worked,
>>> +    # using "-class" option to ensure it works.  Should make no difference.
>>> +    gdb_test_no_output "maint frame-unwinder enable -class ${class}"
>>> +    check_unwinder_class "${class}" "Y"
>>> +}
>>> diff --git a/gdb/testsuite/gdb.base/maint.exp b/gdb/testsuite/gdb.base/maint.exp
>>> index 2c58ffa36c5..ae7ad0787e6 100644
>>> --- a/gdb/testsuite/gdb.base/maint.exp
>>> +++ b/gdb/testsuite/gdb.base/maint.exp
>>> @@ -454,10 +454,6 @@ gdb_test_no_output "maint info line-table xxx.c" \
>>>   
>>>   set timeout $oldtimeout
>>>   
>>> -# Just check that the DWARF unwinders control flag is visible.
>>> -gdb_test "maint show dwarf unwinders" \
>>> -    "The DWARF stack unwinders are currently (on|off)\\."
>>> -
>>>   #============test help on maint commands
>>>   
>>>   test_prefix_command_help {"maint info" "maintenance info"} {
>>> -- 
>>> 2.47.0
>> ---
>>
>> diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
>> index 1417651108f..f3019b7ec18 100644
>> --- a/gdb/frame-unwind.c
>> +++ b/gdb/frame-unwind.c
>> @@ -40,6 +40,7 @@ static const char * unwind_class_conversion[] =
>>     "EXTENSION",
>>     "DEBUGINFO",
>>     "ARCH",
>> +  nullptr
>>   };
>>   
>>   /* Default sniffers, that must always be the first in the unwinder list,
>> @@ -579,6 +580,29 @@ enable_disable_frame_unwinders (const char *args, int from_tty, bool enable)
>>     reinit_frame_cache ();
>>   }
>>   
>> +/* Completer for the "maint frame-unwinder enable|disable" commands.  */
>> +
>> +static void
>> +enable_disable_frame_unwinders_completer (struct cmd_list_element *ignore,
>> +					  completion_tracker &tracker,
>> +					  const char *text,
>> +					  const char */*word*/)
> Would it be alright to write "const char * /*word*/" ? the */* is 
> confusing my editor and it looks like malformed comments, and if I add 
> the space, the red highlights go away.

Sure.  I just copied this from elsewhere in GDB :)

Thanks,
Andrew


>
> -- 
> Cheers,
> Guinevere Larsen
> She/Her/Hers
>
>> +{
>> +  maint_frame_unwind_options opts;
>> +  const auto group = make_frame_unwind_enable_disable_options (&opts);
>> +
>> +  const char *start = text;
>> +  if (gdb::option::complete_options
>> +      (tracker, &text, gdb::option::PROCESS_OPTIONS_UNKNOWN_IS_OPERAND, group))
>> +    return;
>> +
>> +  /* Only complete a class name as a stand-alone operand when no options
>> +     are given.  */
>> +  if (start == text)
>> +    complete_on_enum (tracker, unwind_class_conversion, text, text);
>> +  return;
>> +}
>> +
>>   /* Implement "maint frame-unwinder disable" command.  */
>>   static void
>>   maintenance_disable_frame_unwinders (const char *args, int from_tty)
>> @@ -613,8 +637,9 @@ Unwinders are listed starting with the highest priority."),
>>   			_("Commands handling frame unwinders."),
>>   			&maint_frame_unwinder, 0, &maintenancelist);
>>   
>> -  add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
>> -	   _("\
>> +  cmd_list_element *c
>> +    = add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
>> +	       _("\
>>   Disable one or more frame unwinder(s).\n\
>>   Usage: maint frame-unwinder disable [-all | -name NAME | [-class] CLASS]\n\
>>   \n\
>> @@ -628,10 +653,13 @@ These are the meanings of the options:\n\
>>   \t\tARCH      - Unwinders that use architecture-specific information;\n\
>>   \n\
>>   UNWINDER and NAME are case insensitive."),
>> -	   &maint_frame_unwinder);
>> +	       &maint_frame_unwinder);
>> +  set_cmd_completer_handle_brkchars (c,
>> +				     enable_disable_frame_unwinders_completer);
>>   
>> -  add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
>> -	   _("\
>> +  c =
>> +    add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
>> +	     _("\
>>   Enable one or more frame unwinder(s).\n\
>>   Usage: maint frame-unwinder enable [-all | -name NAME | [-class] CLASS]\n\
>>   \n\
>> @@ -645,5 +673,7 @@ These are the meanings of the options:\n\
>>   \t\tARCH      - Unwinders that use architecture-specific information;\n\
>>   \n\
>>   UNWINDER and NAME are case insensitive."),
>> -	   &maint_frame_unwinder);
>> +	     &maint_frame_unwinder);
>> +  set_cmd_completer_handle_brkchars (c,
>> +				     enable_disable_frame_unwinders_completer);
>>   }
>>
  

On 1/17/25 10:55 AM, Andrew Burgess wrote:
> Guinevere Larsen <guinevere@redhat.com> writes:
>
>> On 1/16/25 9:06 AM, Andrew Burgess wrote:
>>> Guinevere Larsen <guinevere@redhat.com> writes:
>>>
>>>> Sometimes, in the GDB testsuite, we want to test the ability of specific
>>>> unwinders to handle some piece of code. Usually this is done by trying
>>>> to outsmart GDB, or by coercing the compiler to remove information that
>>>> GDB would rely on.  Both approaches have problems as GDB gets smarter
>>>> with time, and that compilers might differ in version and behavior, or
>>>> simply introduce new useful information. This was requested back in 2003
>>>> in PR backtrace/8434.
>>>>
>>>> To improve our ability to thoroughly test GDB, this patch introduces a
>>>> new maintenance command that allows a user to disable some unwinders,
>>>> based on either the name of the unwinder or on its class. With this
>>>> change, it will now be possible for GDB to not find any frame unwinders
>>>> for a given frame, which would previously cause GDB to assert. GDB will
>>>> now check if any frame unwinder has been disabled, and if some has, it
>>>> will just error out instead of asserting.
>>>>
>>>> Unwinders can be disabled or re-enabled in 3 different ways:
>>>> * Disabling/enabling all at once (using '-all').
>>>> * By specifying an unwinder class to be disabled (option '-class').
>>>> * By specifying the name of an unwinder (option '-name').
>>>>
>>>> If you give no options to the command, GDB assumes the input is an
>>>> unwinder class. '-class' would make no difference if used, is just here
>>>> for completeness.
>>>>
>>>> This command is meant to be used once the inferior is already at the
>>>> desired location for the test. An example session would be:
>>>>
>>>> (gdb) start
>>>> Temporary breakpoint 1, main () at omp.c:17
>>>> 17          func();
>>>> (gdb) maint frame-unwinder disable ARCH
>>>> (gdb) bt
>>>> \#0  main () at omp.c:17
>>>> (gdb) maint frame-unwinder enable ARCH
>>>> (gdb) cont
>>>> Continuing.
>>>>
>>>> This commit is a more generic version of commit 3c3bb0580be0,
>>>> and so, based on the final paragraph of the commit message:
>>>>       gdb: Add switch to disable DWARF stack unwinders
>>>> <...>
>>>>       If in the future we find ourselves adding more switches to disable
>>>>       different unwinders, then we should probably move to a more generic
>>>>       solution, and remove this patch.
>>>> this patch also reverts 3c3bb0580be0
>>>>
>>>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=8434
>>>> Reviewed-By: Eli Zaretskii <eliz@gnu.org>
>>>> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
>>>> ---
>>>>    gdb/NEWS                                      |  17 ++
>>>>    gdb/doc/gdb.texinfo                           |  49 ++--
>>>>    gdb/dwarf2/frame-tailcall.c                   |   3 -
>>>>    gdb/dwarf2/frame.c                            |  30 ---
>>>>    gdb/dwarf2/frame.h                            |   6 -
>>>>    gdb/frame-unwind.c                            | 237 +++++++++++++++++-
>>>>    gdb/frame-unwind.h                            |   9 +
>>>>    .../gdb.base/frame-info-consistent.exp        |   8 +-
>>>>    gdb/testsuite/gdb.base/frame-unwind-disable.c |  22 ++
>>>>    .../gdb.base/frame-unwind-disable.exp         | 137 ++++++++++
>>>>    gdb/testsuite/gdb.base/maint.exp              |   4 -
>>>>    11 files changed, 437 insertions(+), 85 deletions(-)
>>>>    create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.c
>>>>    create mode 100644 gdb/testsuite/gdb.base/frame-unwind-disable.exp
>>>>
>>>> diff --git a/gdb/NEWS b/gdb/NEWS
>>>> index 245b355669a..ef3317c11cb 100644
>>>> --- a/gdb/NEWS
>>>> +++ b/gdb/NEWS
>>>> @@ -125,6 +125,13 @@ maintenance info blocks [ADDRESS]
>>>>      are listed starting at the inner global block out to the most inner
>>>>      block.
>>>>    
>>>> +maintenance frame-unwinder disable [-all | -name NAME | [-class] CLASS]
>>>> +maintenance frame-unwinder enable [-all | -name NAME | [-class] CLASS]
>>>> +  Enable or disable frame unwinders.  This is only meant to be used when
>>>> +  testing unwinders themselves, and you want to ensure that a fallback
>>>> +  algorithm won't obscure a regression.  GDB is not expected to behave
>>>> +  well if you try to execute the inferior with unwinders disabled.
>>>> +
>>>>    info missing-objfile-handlers
>>>>      List all the registered missing-objfile handlers.
>>>>    
>>>> @@ -167,6 +174,16 @@ maintenance print remote-registers
>>>>    mainenance info frame-unwinders
>>>>      Add a CLASS column to the output.  This class is a somewhat arbitrary
>>>>      grouping of unwinders, based on which area of GDB adds the unwinder.
>>>> +  Also add an ENABLED column, that will show if the unwinder is enabled
>>>> +  or not.
>>>> +
>>>> +maintenance set dwarf unwinders (on|off)
>>>> +  This command has been removed because the same functionality can be
>>>> +  achieved with maint frame-unwinder (enable|disable) DEBUGINFO.
>>>> +
>>>> +maintenance show dwarf unwinders
>>>> +  This command has been removed since the functionality can be achieved
>>>> +  by checking the last column of maint info frame-unwinders.
>>>>    
>>>>    show configuration
>>>>      Now includes the version of GNU Readline library that GDB is using.
>>>> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
>>>> index 115c1f46b7f..10e6654a03b 100644
>>>> --- a/gdb/doc/gdb.texinfo
>>>> +++ b/gdb/doc/gdb.texinfo
>>>> @@ -42210,31 +42210,6 @@ On hosts without threading, or where worker threads have been disabled
>>>>    at runtime, this setting has no effect, as DWARF reading is always
>>>>    done on the main thread, and is therefore always synchronous.
>>>>    
>>>> -@kindex maint set dwarf unwinders
>>>> -@kindex maint show dwarf unwinders
>>>> -@item maint set dwarf unwinders
>>>> -@itemx maint show dwarf unwinders
>>>> -Control use of the DWARF frame unwinders.
>>>> -
>>>> -@cindex DWARF frame unwinders
>>>> -Many targets that support DWARF debugging use @value{GDBN}'s DWARF
>>>> -frame unwinders to build the backtrace.  Many of these targets will
>>>> -also have a second mechanism for building the backtrace for use in
>>>> -cases where DWARF information is not available, this second mechanism
>>>> -is often an analysis of a function's prologue.
>>>> -
>>>> -In order to extend testing coverage of the second level stack
>>>> -unwinding mechanisms it is helpful to be able to disable the DWARF
>>>> -stack unwinders, this can be done with this switch.
>>>> -
>>>> -In normal use of @value{GDBN} disabling the DWARF unwinders is not
>>>> -advisable, there are cases that are better handled through DWARF than
>>>> -prologue analysis, and the debug experience is likely to be better
>>>> -with the DWARF frame unwinders enabled.
>>>> -
>>>> -If DWARF frame unwinders are not supported for a particular target
>>>> -architecture, then enabling this flag does not cause them to be used.
>>>> -
>>>>    @kindex maint info frame-unwinders
>>>>    @item maint info frame-unwinders
>>>>    List the frame unwinders currently in effect, starting with the highest
>>>> @@ -42252,6 +42227,30 @@ Unwinders installed by debug information readers.
>>>>    Unwinders installed by the architecture specific code.
>>>>    @end table
>>>>    
>>>> +@kindex maint frame-unwinder disable
>>>> +@kindex maint frame-unwinder enable
>>>> +@item maint frame-unwinder disable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
>>>> +@item maint frame-unwinder enable [@code{-all} | @code{-name} @var{name} | [@code{-class}] @var{class}]
>>>> +Disable or enable frame unwinders.  This is meant only as a testing tool, and
>>>> +@value{GDBN} is not guaranteed to work properly if it is unable to find
>>>> +valid frame unwinders.
>>>> +
>>>> +The meaning of each of the invocations are as follows:
>>>> +
>>>> +@table @samp
>>>> +@item @code{-all}
>>>> +Disable or enable all unwinders.
>>>> +@item @code{-name} @var{name}
>>>> +@var{name} is the exact name of the unwinder to be disabled or enabled.
>>>> +@item [@code{-class}] @var{class}
>>>> +@var{class} is the class of frame unwinders to be disabled or enabled.
>>>> +The class may include the prefix @code{FRAME_UNWINDER_}, but it is not
>>>> +required.
>>>> +@end table
>>>> +
>>>> +@var{name} and @var{class} are always case insensitive.  If no option
>>>> +starting wth @code{-} is given, @value{GDBN} assumes @code{-class}.
>>>> +
>>>>    @kindex maint set worker-threads
>>>>    @kindex maint show worker-threads
>>>>    @item maint set worker-threads
>>>> diff --git a/gdb/dwarf2/frame-tailcall.c b/gdb/dwarf2/frame-tailcall.c
>>>> index 54813d00b03..2d7ab740f62 100644
>>>> --- a/gdb/dwarf2/frame-tailcall.c
>>>> +++ b/gdb/dwarf2/frame-tailcall.c
>>>> @@ -321,9 +321,6 @@ tailcall_frame_sniffer (const struct frame_unwind *self,
>>>>      int next_levels;
>>>>      struct tailcall_cache *cache;
>>>>    
>>>> -  if (!dwarf2_frame_unwinders_enabled_p)
>>>> -    return 0;
>>>> -
>>>>      /* Inner tail call element does not make sense for a sentinel frame.  */
>>>>      next_frame = get_next_frame (this_frame);
>>>>      if (next_frame == NULL)
>>>> diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
>>>> index 85e1d59bc09..e0e8eb5dbec 100644
>>>> --- a/gdb/dwarf2/frame.c
>>>> +++ b/gdb/dwarf2/frame.c
>>>> @@ -183,9 +183,6 @@ static ULONGEST read_encoded_value (struct comp_unit *unit, gdb_byte encoding,
>>>>    				    unrelocated_addr func_base);
>>>>    
>>>>    
>>>> -/* See dwarf2/frame.h.  */
>>>> -bool dwarf2_frame_unwinders_enabled_p = true;
>>>> -
>>>>    /* Store the length the expression for the CFA in the `cfa_reg' field,
>>>>       which is unused in that case.  */
>>>>    #define cfa_exp_len cfa_reg
>>>> @@ -1306,9 +1303,6 @@ static int
>>>>    dwarf2_frame_sniffer (const struct frame_unwind *self,
>>>>    		      const frame_info_ptr &this_frame, void **this_cache)
>>>>    {
>>>> -  if (!dwarf2_frame_unwinders_enabled_p)
>>>> -    return 0;
>>>> -
>>>>      /* Grab an address that is guaranteed to reside somewhere within the
>>>>         function.  get_frame_pc(), with a no-return next function, can
>>>>         end up returning something past the end of this function's body.
>>>> @@ -2253,34 +2247,10 @@ dwarf2_build_frame_info (struct objfile *objfile)
>>>>      set_comp_unit (objfile, unit.release ());
>>>>    }
>>>>    
>>>> -/* Handle 'maintenance show dwarf unwinders'.  */
>>>> -
>>>> -static void
>>>> -show_dwarf_unwinders_enabled_p (struct ui_file *file, int from_tty,
>>>> -				struct cmd_list_element *c,
>>>> -				const char *value)
>>>> -{
>>>> -  gdb_printf (file,
>>>> -	      _("The DWARF stack unwinders are currently %s.\n"),
>>>> -	      value);
>>>> -}
>>>> -
>>>>    void _initialize_dwarf2_frame ();
>>>>    void
>>>>    _initialize_dwarf2_frame ()
>>>>    {
>>>> -  add_setshow_boolean_cmd ("unwinders", class_obscure,
>>>> -			   &dwarf2_frame_unwinders_enabled_p , _("\
>>>> -Set whether the DWARF stack frame unwinders are used."), _("\
>>>> -Show whether the DWARF stack frame unwinders are used."), _("\
>>>> -When enabled the DWARF stack frame unwinders can be used for architectures\n\
>>>> -that support the DWARF unwinders.  Enabling the DWARF unwinders for an\n\
>>>> -architecture that doesn't support them will have no effect."),
>>>> -			   NULL,
>>>> -			   show_dwarf_unwinders_enabled_p,
>>>> -			   &set_dwarf_cmdlist,
>>>> -			   &show_dwarf_cmdlist);
>>>> -
>>>>    #if GDB_SELF_TEST
>>>>      selftests::register_test_foreach_arch ("execute_cfa_program",
>>>>    					 selftests::execute_cfa_program_test);
>>>> diff --git a/gdb/dwarf2/frame.h b/gdb/dwarf2/frame.h
>>>> index 2167310fbdf..fe2d669a983 100644
>>>> --- a/gdb/dwarf2/frame.h
>>>> +++ b/gdb/dwarf2/frame.h
>>>> @@ -198,12 +198,6 @@ struct dwarf2_frame_state
>>>>      bool armcc_cfa_offsets_reversed = false;
>>>>    };
>>>>    
>>>> -/* When this is true the DWARF frame unwinders can be used if they are
>>>> -   registered with the gdbarch.  Not all architectures can or do use the
>>>> -   DWARF unwinders.  Setting this to true on a target that does not
>>>> -   otherwise support the DWARF unwinders has no effect.  */
>>>> -extern bool dwarf2_frame_unwinders_enabled_p;
>>>> -
>>>>    /* Set the architecture-specific register state initialization
>>>>       function for GDBARCH to INIT_REG.  */
>>>>    
>>>> diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
>>>> index 3ab6af1c4da..968bb846402 100644
>>>> --- a/gdb/frame-unwind.c
>>>> +++ b/gdb/frame-unwind.c
>>>> @@ -29,6 +29,7 @@
>>>>    #include "gdbarch.h"
>>>>    #include "dwarf2/frame-tailcall.h"
>>>>    #include "cli/cli-cmds.h"
>>>> +#include "cli/cli-option.h"
>>>>    #include "inferior.h"
>>>>    
>>>>    /* Conversion list between the enum for frame_unwind_class and
>>>> @@ -89,6 +90,20 @@ frame_unwinder_class_str (frame_unwind_class uclass)
>>>>      return unwind_class_conversion[uclass];
>>>>    }
>>>>    
>>>> +/* Case insensitive search for a frame_unwind_class based on the given
>>>> +   string.  */
>>>> +static enum frame_unwind_class
>>>> +str_to_frame_unwind_class (const char *class_str)
>>>> +{
>>>> +  for (int i = 0; i < UNWIND_CLASS_NUMBER; i++)
>>>> +    {
>>>> +      if (strcasecmp (unwind_class_conversion[i], class_str) == 0)
>>>> +	return (frame_unwind_class) i;
>>>> +    }
>>>> +
>>>> +  error (_("Unknown frame unwind class: %s"), class_str);
>>>> +}
>>>> +
>>>>    void
>>>>    frame_unwind_prepend_unwinder (struct gdbarch *gdbarch,
>>>>    				const struct frame_unwind *unwinder)
>>>> @@ -175,27 +190,46 @@ frame_unwind_find_by_frame (const frame_info_ptr &this_frame, void **this_cache)
>>>>      FRAME_SCOPED_DEBUG_ENTER_EXIT;
>>>>      frame_debug_printf ("this_frame=%d", frame_relative_level (this_frame));
>>>>    
>>>> -  const struct frame_unwind *unwinder_from_target;
>>>> +  /* If we see a disabled unwinder, we assume some test is being run on
>>>> +     GDB, and we don't want to internal_error at the end of this function.  */
>>>> +  bool seen_disabled_unwinder = false;
>>>> +  /* Lambda to factor out the logic of checking if an unwinder is enabled,
>>>> +     testing it and otherwise recording if we saw a disable unwinder.  */
>>>> +  auto test_unwinder = [&] (const struct frame_unwind *unwinder)
>>>> +    {
>>>> +      if (unwinder == nullptr)
>>>> +	return false;
>>>> +
>>>> +      if (!unwinder->enabled ())
>>>> +	{
>>>> +	  seen_disabled_unwinder = true;
>>>> +	  return false;
>>>> +	}
>>>> +
>>>> +      return frame_unwind_try_unwinder (this_frame,
>>>> +					this_cache,
>>>> +					unwinder);
>>>> +    };
>>>>    
>>>> -  unwinder_from_target = target_get_unwinder ();
>>>> -  if (unwinder_from_target != NULL
>>>> -      && frame_unwind_try_unwinder (this_frame, this_cache,
>>>> -				   unwinder_from_target))
>>>> +  if (test_unwinder (target_get_unwinder ()))
>>>>        return;
>>>>    
>>>> -  unwinder_from_target = target_get_tailcall_unwinder ();
>>>> -  if (unwinder_from_target != NULL
>>>> -      && frame_unwind_try_unwinder (this_frame, this_cache,
>>>> -				   unwinder_from_target))
>>>> +  if (test_unwinder (target_get_tailcall_unwinder ()))
>>>>        return;
>>>>    
>>>>      struct gdbarch *gdbarch = get_frame_arch (this_frame);
>>>>      std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>>>>      for (auto unwinder : *table)
>>>> -    if (frame_unwind_try_unwinder (this_frame, this_cache, unwinder))
>>>> -      return;
>>>> +    {
>>>> +      if (test_unwinder (unwinder))
>>>> +	return;
>>>> +    }
>>>>    
>>>> -  internal_error (_("frame_unwind_find_by_frame failed"));
>>>> +  if (seen_disabled_unwinder)
>>>> +    error (_("Required frame unwinder may have been disabled"
>>>> +	     ", see 'maint info frame-unwinders'"));
>>>> +  else
>>>> +    internal_error (_("frame_unwind_find_by_frame failed"));
>>>>    }
>>>>    
>>>>    /* A default frame sniffer which always accepts the frame.  Used by
>>>> @@ -394,10 +428,11 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>>>>      std::vector<const frame_unwind *> *table = get_frame_unwind_table (gdbarch);
>>>>    
>>>>      ui_out *uiout = current_uiout;
>>>> -  ui_out_emit_table table_emitter (uiout, 3, -1, "FrameUnwinders");
>>>> +  ui_out_emit_table table_emitter (uiout, 4, -1, "FrameUnwinders");
>>>>      uiout->table_header (27, ui_left, "name", "Name");
>>>>      uiout->table_header (25, ui_left, "type", "Type");
>>>>      uiout->table_header (9, ui_left, "class", "Class");
>>>> +  uiout->table_header (8, ui_left, "enabled", "Enabled");
>>>>      uiout->table_body ();
>>>>    
>>>>      for (auto unwinder : *table)
>>>> @@ -407,10 +442,145 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
>>>>          uiout->field_string ("type", frame_type_str (unwinder->type ()));
>>>>          uiout->field_string ("class", frame_unwinder_class_str (
>>>>    					unwinder->unwinder_class ()));
>>>> +      uiout->field_string ("enabled", unwinder->enabled () ? "Y" : "N");
>>>>          uiout->text ("\n");
>>>>        }
>>>>    }
>>>>    
>>>> +/* Options for disabling frame unwinders.  */
>>>> +struct maint_frame_unwind_options
>>>> +{
>>>> +  std::string unwinder_name;
>>>> +  const char *unwinder_class = nullptr;
>>>> +  bool all = false;
>>>> +};
>>>> +
>>>> +static const gdb::option::option_def maint_frame_unwind_opt_defs[] = {
>>>> +
>>>> +  gdb::option::flag_option_def<maint_frame_unwind_options> {
>>>> +    "all",
>>>> +    [] (maint_frame_unwind_options *opt) { return &opt->all; },
>>>> +    nullptr,
>>>> +    N_("Change the state of all unwinders")
>>>> +  },
>>>> +  gdb::option::string_option_def<maint_frame_unwind_options> {
>>>> +    "name",
>>>> +    [] (maint_frame_unwind_options *opt) { return &opt->unwinder_name; },
>>>> +    nullptr,
>>>> +    N_("The name of the unwinder to have its state changed")
>>>> +  },
>>>> +  gdb::option::enum_option_def<maint_frame_unwind_options> {
>>>> +    "class",
>>>> +    unwind_class_conversion,
>>>> +    [] (maint_frame_unwind_options *opt) { return &opt->unwinder_class; },
>>>> +    nullptr,
>>>> +    N_("The class of unwinders to have their states changed")
>>>> +  }
>>>> +};
>>>> +
>>>> +static inline gdb::option::option_def_group
>>>> +make_frame_unwind_enable_disable_options (maint_frame_unwind_options *opts)
>>>> +{
>>>> +  return {{maint_frame_unwind_opt_defs}, opts};
>>>> +}
>>>> +
>>>> +/* Helper function to both enable and disable frame unwinders.
>>>> +   If ENABLE is true, this call will be enabling unwinders,
>>>> +   otherwise the unwinders will be disabled.  */
>>>> +static void
>>>> +enable_disable_frame_unwinders (const char *args, int from_tty, bool enable)
>>>> +{
>>>> +  if (args == nullptr)
>>>> +    {
>>>> +      if (enable)
>>>> +	error (_("Specify which frame unwinder(s) should be enabled"));
>>>> +      else
>>>> +	error (_("Specify which frame unwinder(s) should be disabled"));
>>>> +    }
>>>> +
>>>> +  struct gdbarch* gdbarch = current_inferior ()->arch ();
>>>> +  std::vector<const frame_unwind *> *unwinder_list
>>>> +    = get_frame_unwind_table (gdbarch);
>>>> +
>>>> +  maint_frame_unwind_options opts;
>>>> +  gdb::option::process_options
>>>> +    (&args, gdb::option::PROCESS_OPTIONS_UNKNOWN_IS_ERROR,
>>>> +     make_frame_unwind_enable_disable_options (&opts));
>>>> +
>>>> +  if ((opts.all && !opts.unwinder_name.empty ())
>>>> +      || (opts.all && opts.unwinder_class != nullptr)
>>>> +      || (!opts.unwinder_name.empty () && opts.unwinder_class != nullptr))
>>>> +    error (_("Options are mutually exclusive"));
>>>> +
>>>> +  /* First see if the user wants to change all unwinders.  */
>>>> +  if (opts.all)
>>>> +    {
>>>> +      for (const frame_unwind *u : *unwinder_list)
>>>> +	u->set_enabled (enable);
>>>> +
>>>> +      reinit_frame_cache ();
>>>> +      return;
>>>> +    }
>>>> +
>>>> +  /* If user entered a specific unwinder name, handle it here.  If the
>>>> +     unwinder is already at the expected state, error out.  */
>>>> +  if (!opts.unwinder_name.empty ())
>>>> +    {
>>>> +      bool did_something = false;
>>>> +      for (const frame_unwind *unwinder : *unwinder_list)
>>>> +	{
>>>> +	  if (strcasecmp (unwinder->name (),
>>>> +			  opts.unwinder_name.c_str ()) == 0)
>>>> +	    {
>>>> +	      if (unwinder->enabled () == enable)
>>>> +		{
>>>> +		  if (unwinder->enabled ())
>>>> +		    error (_("unwinder %s is already enabled"),
>>>> +			     unwinder->name ());
>>>> +		  else
>>>> +		    error (_("unwinder %s is already disabled"),
>>>> +			     unwinder->name ());
>>>> +		}
>>>> +	      unwinder->set_enabled (enable);
>>>> +
>>>> +	      did_something = true;
>>>> +	      break;
>>>> +	    }
>>>> +	}
>>>> +      if (!did_something)
>>>> +	error (_("couldn't find unwinder named %s"),
>>>> +	       opts.unwinder_name.c_str ());
>>>> +    }
>>>> +  else
>>>> +    {
>>>> +      if (opts.unwinder_class == nullptr)
>>>> +	opts.unwinder_class = args;
>>>> +      enum frame_unwind_class dclass = str_to_frame_unwind_class
>>>> +	(opts.unwinder_class);
>>>> +      for (auto unwinder: *unwinder_list)
>>> I think you should stick with the form you use earlier:
>>>
>>>     (const frame_unwind *unwinder : *unwinder_list)
>>>
>>> But if you really want to stick with auto, then I think:
>>>
>>>    (const auto &unwinder : *unwinder_list)
>>>
>>> would be OK.
>>>
>>>
>>>> +	{
>>>> +	  if (unwinder->unwinder_class () == dclass)
>>>> +	    unwinder->set_enabled (enable);
>>>> +	}
>>>> +    }
>>>> +
>>>> +  reinit_frame_cache ();
>>>> +}
>>>> +
>>>> +/* Implement "maint frame-unwinder disable" command.  */
>>>> +static void
>>>> +maintenance_disable_frame_unwinders (const char *args, int from_tty)
>>>> +{
>>>> +  enable_disable_frame_unwinders (args, from_tty, false);
>>>> +}
>>>> +
>>>> +/* Implement "maint frame-unwinder enable" command.  */
>>>> +static void
>>>> +maintenance_enable_frame_unwinders (const char *args, int from_tty)
>>>> +{
>>>> +  enable_disable_frame_unwinders (args, from_tty, true);
>>>> +}
>>>> +
>>>>    void _initialize_frame_unwind ();
>>>>    void
>>>>    _initialize_frame_unwind ()
>>>> @@ -423,4 +593,45 @@ _initialize_frame_unwind ()
>>>>    List the frame unwinders currently in effect.\n\
>>>>    Unwinders are listed starting with the highest priority."),
>>>>    	   &maintenanceinfolist);
>>>> +
>>>> +  /* Add "maint frame-unwinder disable/enable".  */
>>>> +  static struct cmd_list_element *maint_frame_unwinder;
>>>> +
>>>> +  add_basic_prefix_cmd ("frame-unwinder", class_maintenance,
>>>> +			_("Commands handling frame unwinders."),
>>>> +			&maint_frame_unwinder, 0, &maintenancelist);
>>>> +
>>>> +  add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
>>>> +	   _("\
>>>> +Disable one or more frame unwinder(s).\n\
>>>> +Usage: maint frame-unwinder disable [-all | -name NAME | [-class] CLASS]\n\
>>>> +\n\
>>>> +These are the meanings of the options:\n\
>>>> +\t-all    - All available unwinders will be disabled\n\
>>>> +\t-name   - NAME is the exact name of the frame unwinder to be disabled\n\
>>>> +\t-class  - CLASS is the class of unwinders to be disabled. Valid classes are:\n\
>>>> +\t\tGDB       - Unwinders added by GDB core;\n\
>>>> +\t\tEXTENSION - Unwinders added by extension languages;\n\
>>>> +\t\tDEBUGINFO - Unwinders that handle debug information;\n\
>>>> +\t\tARCH      - Unwinders that use architecture-specific information;\n\
>>>> +\n\
>>>> +UNWINDER and NAME are case insensitive."),
>>>> +	   &maint_frame_unwinder);
>>>> +
>>>> +  add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
>>>> +	   _("\
>>>> +Enable one or more frame unwinder(s).\n\
>>>> +Usage: maint frame-unwinder enable [-all | -name NAME | [-class] CLASS]\n\
>>>> +\n\
>>>> +These are the meanings of the options:\n\
>>>> +\t-all    - All available unwinders will be enabled\n\
>>>> +\t-name   - NAME is the exact name of the frame unwinder to be enabled\n\
>>>> +\t-class  - CLASS is the class of unwinders to be enabled. Valid classes are:\n\
>>>> +\t\tGDB       - Unwinders added by GDB core;\n\
>>>> +\t\tEXTENSION - Unwinders added by extension languages;\n\
>>>> +\t\tDEBUGINFO - Unwinders that handle debug information;\n\
>>>> +\t\tARCH      - Unwinders that use architecture-specific information;\n\
>>>> +\n\
>>>> +UNWINDER and NAME are case insensitive."),
>>>> +	   &maint_frame_unwinder);
>>>>    }
>>> At the bottom of this email you'll find a small patch which applies on
>>> top of this and adds some basic command completion.  It doesn't complete
>>> the NAMEs, I'm not sure if there's a good way to do that (yet).  It also
>>> doesn't switch the help text to use the %OPTIONS% mechanism, I tried
>>> that, but I think there may be some bugs with the formatting (I'll look
>>> into it), so I've left that off.
>>>
>>> You don't have to, we can add completion later, but I do think it would
>>> be good to merge the patch below with this one.  But it is up to you.
>>> Take a look and see what you think.
>>>
>>>> diff --git a/gdb/frame-unwind.h b/gdb/frame-unwind.h
>>>> index 13f18618d24..adf8b47982c 100644
>>>> --- a/gdb/frame-unwind.h
>>>> +++ b/gdb/frame-unwind.h
>>>> @@ -192,6 +192,12 @@ class frame_unwind
>>>>      const frame_data *unwind_data () const
>>>>      { return m_unwind_data; }
>>>>    
>>>> +  bool enabled () const
>>>> +  { return m_enabled; }
>>>> +
>>>> +  void set_enabled (bool state) const
>>>> +  { m_enabled = state; }
>>>> +
>>>>      /* Default stop_reason implementation.  It reports NO_REASON, unless the
>>>>         frame is the outermost.  */
>>>>    
>>>> @@ -245,6 +251,9 @@ class frame_unwind
>>>>      frame_unwind_class m_unwinder_class;
>>>>    
>>>>      const frame_data *m_unwind_data;
>>>> +
>>>> +  /* Whether this unwinder can be used when sniffing.  */
>>>> +  mutable bool m_enabled = true;
>>>>    };
>>>>    
>>>>    /* This is a legacy version of the frame unwinder.  The original struct
>>>> diff --git a/gdb/testsuite/gdb.base/frame-info-consistent.exp b/gdb/testsuite/gdb.base/frame-info-consistent.exp
>>>> index fe0cfad95bc..4f483111a91 100644
>>>> --- a/gdb/testsuite/gdb.base/frame-info-consistent.exp
>>>> +++ b/gdb/testsuite/gdb.base/frame-info-consistent.exp
>>>> @@ -95,11 +95,11 @@ proc compare_frames {frames} {
>>>>        }
>>>>    }
>>>>    
>>>> -proc test {dwarf_unwinder} {
>>>> +proc test {enable} {
>>>>    
>>>>        clean_restart $::binfile
>>>>    
>>>> -    gdb_test_no_output "maint set dwarf unwinder $dwarf_unwinder"
>>>> +    gdb_test_no_output "maint frame-unwinder $enable DEBUGINFO"
>>>>    
>>>>        if {![runto_main]} {
>>>>    	return 0
>>>> @@ -134,6 +134,6 @@ proc test {dwarf_unwinder} {
>>>>        }
>>>>    }
>>>>    
>>>> -foreach_with_prefix dwarf {"off" "on"} {
>>>> -    test $dwarf
>>>> +foreach_with_prefix action {"disable" "enable"} {
>>>> +    test $action
>>>>    }
>>>> diff --git a/gdb/testsuite/gdb.base/frame-unwind-disable.c b/gdb/testsuite/gdb.base/frame-unwind-disable.c
>>>> new file mode 100644
>>>> index 00000000000..bbcfb01316e
>>>> --- /dev/null
>>>> +++ b/gdb/testsuite/gdb.base/frame-unwind-disable.c
>>>> @@ -0,0 +1,22 @@
>>>> +/* This testcase is part of GDB, the GNU debugger.
>>>> +
>>>> +   Copyright 2024 Free Software Foundation, Inc.
>>> Remember to update the copyright date when rebasing.
>>>
>>>> +
>>>> +   This program is free software; you can redistribute it and/or modify
>>>> +   it under the terms of the GNU General Public License as published by
>>>> +   the Free Software Foundation; either version 3 of the License, or
>>>> +   (at your option) any later version.
>>>> +
>>>> +   This program is distributed in the hope that it will be useful,
>>>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>>> +   GNU General Public License for more details.
>>>> +
>>>> +   You should have received a copy of the GNU General Public License
>>>> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
>>>> +
>>>> +int
>>>> +main ()
>>>> +{
>>>> +  return 0;
>>>> +}
>>>> diff --git a/gdb/testsuite/gdb.base/frame-unwind-disable.exp b/gdb/testsuite/gdb.base/frame-unwind-disable.exp
>>>> new file mode 100644
>>>> index 00000000000..f4cad9a47fd
>>>> --- /dev/null
>>>> +++ b/gdb/testsuite/gdb.base/frame-unwind-disable.exp
>>>> @@ -0,0 +1,137 @@
>>>> +# Copyright 2024 Free Software Foundation, Inc.
>>> And again with the date.
>>>
>>>> +
>>>> +# This program is free software; you can redistribute it and/or modify
>>>> +# it under the terms of the GNU General Public License as published by
>>>> +# the Free Software Foundation; either version 3 of the License, or
>>>> +# (at your option) any later version.
>>>> +#
>>>> +# This program is distributed in the hope that it will be useful,
>>>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>>> +# GNU General Public License for more details.
>>>> +#
>>>> +# You should have received a copy of the GNU General Public License
>>>> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
>>>> +
>>>> +# Test multiple situations in which we may use the maintenance command to
>>>> +# disable and enable frame unwinders, and check that they really are
>>>> +# disabled when they say the are.
>>>> +
>>>> +standard_testfile .c
>>> You can drop '.c' here, it's the default.
>>>
>>>> +
>>>> +# Proc to check if the unwinder of the given name is in the desired state.
>>>> +# STATE can be either Y or N.
>>>> +proc check_unwinder_state { unwinder_name state {testname ""} } {
>>>> +    set should_pass false
>>>> +    set command "maint info frame-unwinders"
>>>> +    if {${testname} == ""} {
>>>> +	set testname "checking state ${state} for ${unwinder_name}"
>>>> +    }
>>>> +    gdb_test_multiple "${command}" "${testname}" -lbl {
>>>> +	-re "${unwinder_name}\\s+\\w+\\s+\\w+\\s+${state}\\s+(?=\r\n)" {
>>>> +	    set should_pass true
>>>> +	    exp_continue
>>>> +	}
>>>> +	-re "${command}" {
>>>> +	    exp_continue
>>>> +	}
>>>> +	-re "\\w+\\s+\\w+\\s+\\w+\\s+\\w+\\s+(?=\r\n)" {
>>>> +	    exp_continue
>>>> +	}
>>>> +	-re -wrap "" {
>>>> +	    gdb_assert ${should_pass} "${gdb_test_name}"
>>> I don't think the quotes around "${gdb_test_name}" are needed here?  In
>>> fact, there seem to be a few places where you place quotes around
>>> expansion of a single variable (e.g. "${command}" on the
>>> gdb_test_multiple line), I don't think any of these are needed.
>>>
>>> With these changes (and with or without the completion patch):
>> I applied all the changes, and I like the idea of adding completion, but
>> I wonder: should we add a test for completion? If so, I think this is
>> better saved for a later patch, so that we can work on a good test and
>> further improve the completion, because it would be nice to also
>> complete for "-class", "-name" and "-all", but I'm not sure how that'd
>> work yet.
>>
>> If a test isn't all that important we can add it now and do more work
>> later on. I also have an inlined styling question
> I'm not sure every function with completion has tests.  We do have some
> general tests that cover completion though.
>
> If it bothers you, then feel free to leave it out for now, I certainly
> don't want to delay this work going in just for completion of a
> maintenance command, you already switched over to the option system for
> me, which means we're better placed to add completion now or later, so
> I'm grateful for that.
>
> The function I proposed should be able to complete the '-class',
> '-name', and '-all' option names.  Additionally, the '-class' value
> should complete.  And the class name as an operand, if there are no
> options given.
Oh, I must have misread the code then. I'm happy adding the completion then!
>
> Completion of -name values is trickier, as the possible set of names can
> change by architecture, and the set of extensions loaded (I think).
> What we really need is for -name to be a "dynamic" enum option, where
> the dynamic property is provided by a callback which gets the list of
> possible enum values.  But such dynamic enums don't currently exist.
> But I might look into adding that feature once this patch lands.
Yeah, I remember we talked about this. It would be a really nice addition!
>
> Anyway, feel free to add the completion, or not.  If not I'll follow up
> afterwards.
>
>>> Approved-By: Andrew Burgess <aburgess@redhat.com>
>>>
>>> Thanks,
>>> Andrew
>>>
>>>> +	}
>>>> +    }
>>>> +}
>>>> +
>>>> +# Check if all unwinders of class UNWINDER_CLASS are in the state STATE.
>>>> +# STATE can be either Y or N.
>>>> +# UNWINDER_CLASS can be one of: GDB, ARCH, EXTENSION, DEBUGINFO.  It can
>>>> +# also be \\w+ if checking all unwinders.
>>>> +proc check_unwinder_class { unwinder_class state {testname ""} } {
>>>> +    set command "maint info frame-unwinders"
>>>> +    set should_pass true
>>>> +    if {$testname == ""} {
>>>> +	set testname "checking if ${unwinder_class} state is ${state}"
>>>> +    }
>>>> +    gdb_test_multiple "${command}" "${testname}" -lbl {
>>>> +	-re "^\[^\r\n\]+\\s+\\w+\\s+${unwinder_class}\\s+\(\[YN\]\)\\s+(?=\r\n)" {
>>>> +	    # The unwinder name may have multiple words, so we need to use the
>>>> +	    # more generic [^\r\n] pattern to match the unwinders.
>>>> +	    set cur_state $expect_out(1,string)
>>>> +	    if {$cur_state == $state} {
>>>> +		set should_pass false
>>>> +	    }
>>>> +	    exp_continue
>>>> +	}
>>>> +	-re "${command}" {
>>>> +	    exp_continue
>>>> +	}
>>>> +	-re -wrap "" {
>>>> +	    gdb_assert ${should_pass} "${gdb_test_name}"
>>>> +	}
>>>> +    }
>>>> +}
>>>> +
>>>> +if {[prepare_for_testing "failed to prepare" ${testfile} ${srcfile}]} {
>>>> +    return -1
>>>> +}
>>>> +
>>>> +if {![runto_main]} {
>>>> +    untested "couldn't run to main"
>>>> +    return
>>>> +}
>>>> +
>>>> +# Test disabling all unwinders.
>>>> +check_unwinder_class "\\w+" "Y" \
>>>> +    "all unwinders enabled before any changes"
>>>> +gdb_test_no_output "maint frame-unwinder disable -all"
>>>> +check_unwinder_class "\\w+" "N" \
>>>> +    "all unwinders were properly disabled"
>>>> +
>>>> +# Test if GDB can still make a backtrace once all unwinders are disabled.
>>>> +# It should be impossible.
>>>> +gdb_test "backtrace" \
>>>> +    ".*Required frame unwinder may have been disabled, see 'maint info frame-unwinders'.*" \
>>>> +    "no suitable unwinders should be found"
>>>> +
>>>> +# Reenable all unwinders.
>>>> +gdb_test_no_output "maint frame-unwinder enable -all"
>>>> +check_unwinder_class "\\w+" "Y" \
>>>> +    "all unwinders should be re-enabled"
>>>> +
>>>> +# Check that we are able to get backtraces once again.
>>>> +gdb_test "backtrace" ".0\\s+main .. at.*" \
>>>> +    "we can get usable backtraces again"
>>>> +
>>>> +# Check if we can disable an unwinder based on the name.
>>>> +check_unwinder_state "dummy" "Y"
>>>> +gdb_test_no_output "maint frame-unwinder disable -name dummy"
>>>> +check_unwinder_state "dummy" "N"
>>>> +# And verify what happens if you try to disable it again.
>>>> +gdb_test "maint frame-unwinder disable -name dummy" \
>>>> +    "unwinder dummy is already disabled" \
>>>> +    "disable already disabled unwinder"
>>>> +check_unwinder_state "dummy" "N" "dummy should continue disabled"
>>>> +
>>>> +foreach class {GDB ARCH DEBUGINFO EXTENSION} {
>>>> +    # Disable all unwinders of type CLASS, and check that the command worked.
>>>> +    gdb_test_no_output "maint frame-unwinder disable ${class}"
>>>> +    check_unwinder_class "${class}" "N"
>>>> +}
>>>> +
>>>> +# Now check if we are able to enable a single unwinder, and what happens if we
>>>> +# enable it twice.
>>>> +gdb_test_no_output "maint frame-unwinder enable -name dummy"
>>>> +check_unwinder_state "dummy" "Y" "successfully enabled dummy unwinder"
>>>> +gdb_test "maint frame-unwinder enable -name dummy" \
>>>> +    "unwinder dummy is already enabled" \
>>>> +    "enable already enabled unwinder"
>>>> +check_unwinder_state "dummy" "Y" "dummy should continue enabled"
>>>> +
>>>> +foreach class {GDB ARCH DEBUGINFO EXTENSION} {
>>>> +    # Enable all unwinders of type CLASS, and check that the command worked,
>>>> +    # using "-class" option to ensure it works.  Should make no difference.
>>>> +    gdb_test_no_output "maint frame-unwinder enable -class ${class}"
>>>> +    check_unwinder_class "${class}" "Y"
>>>> +}
>>>> diff --git a/gdb/testsuite/gdb.base/maint.exp b/gdb/testsuite/gdb.base/maint.exp
>>>> index 2c58ffa36c5..ae7ad0787e6 100644
>>>> --- a/gdb/testsuite/gdb.base/maint.exp
>>>> +++ b/gdb/testsuite/gdb.base/maint.exp
>>>> @@ -454,10 +454,6 @@ gdb_test_no_output "maint info line-table xxx.c" \
>>>>    
>>>>    set timeout $oldtimeout
>>>>    
>>>> -# Just check that the DWARF unwinders control flag is visible.
>>>> -gdb_test "maint show dwarf unwinders" \
>>>> -    "The DWARF stack unwinders are currently (on|off)\\."
>>>> -
>>>>    #============test help on maint commands
>>>>    
>>>>    test_prefix_command_help {"maint info" "maintenance info"} {
>>>> -- 
>>>> 2.47.0
>>> ---
>>>
>>> diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
>>> index 1417651108f..f3019b7ec18 100644
>>> --- a/gdb/frame-unwind.c
>>> +++ b/gdb/frame-unwind.c
>>> @@ -40,6 +40,7 @@ static const char * unwind_class_conversion[] =
>>>      "EXTENSION",
>>>      "DEBUGINFO",
>>>      "ARCH",
>>> +  nullptr
>>>    };
>>>    
>>>    /* Default sniffers, that must always be the first in the unwinder list,
>>> @@ -579,6 +580,29 @@ enable_disable_frame_unwinders (const char *args, int from_tty, bool enable)
>>>      reinit_frame_cache ();
>>>    }
>>>    
>>> +/* Completer for the "maint frame-unwinder enable|disable" commands.  */
>>> +
>>> +static void
>>> +enable_disable_frame_unwinders_completer (struct cmd_list_element *ignore,
>>> +					  completion_tracker &tracker,
>>> +					  const char *text,
>>> +					  const char */*word*/)
>> Would it be alright to write "const char * /*word*/" ? the */* is
>> confusing my editor and it looks like malformed comments, and if I add
>> the space, the red highlights go away.
> Sure.  I just copied this from elsewhere in GDB :)
>
> Thanks,
> Andrew
>
>
>> -- 
>> Cheers,
>> Guinevere Larsen
>> She/Her/Hers
>>
>>> +{
>>> +  maint_frame_unwind_options opts;
>>> +  const auto group = make_frame_unwind_enable_disable_options (&opts);
>>> +
>>> +  const char *start = text;
>>> +  if (gdb::option::complete_options
>>> +      (tracker, &text, gdb::option::PROCESS_OPTIONS_UNKNOWN_IS_OPERAND, group))
>>> +    return;
>>> +
>>> +  /* Only complete a class name as a stand-alone operand when no options
>>> +     are given.  */
>>> +  if (start == text)
>>> +    complete_on_enum (tracker, unwind_class_conversion, text, text);
>>> +  return;
>>> +}
>>> +
>>>    /* Implement "maint frame-unwinder disable" command.  */
>>>    static void
>>>    maintenance_disable_frame_unwinders (const char *args, int from_tty)
>>> @@ -613,8 +637,9 @@ Unwinders are listed starting with the highest priority."),
>>>    			_("Commands handling frame unwinders."),
>>>    			&maint_frame_unwinder, 0, &maintenancelist);
>>>    
>>> -  add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
>>> -	   _("\
>>> +  cmd_list_element *c
>>> +    = add_cmd ("disable", class_maintenance, maintenance_disable_frame_unwinders,
>>> +	       _("\
>>>    Disable one or more frame unwinder(s).\n\
>>>    Usage: maint frame-unwinder disable [-all | -name NAME | [-class] CLASS]\n\
>>>    \n\
>>> @@ -628,10 +653,13 @@ These are the meanings of the options:\n\
>>>    \t\tARCH      - Unwinders that use architecture-specific information;\n\
>>>    \n\
>>>    UNWINDER and NAME are case insensitive."),
>>> -	   &maint_frame_unwinder);
>>> +	       &maint_frame_unwinder);
>>> +  set_cmd_completer_handle_brkchars (c,
>>> +				     enable_disable_frame_unwinders_completer);
>>>    
>>> -  add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
>>> -	   _("\
>>> +  c =
>>> +    add_cmd ("enable", class_maintenance, maintenance_enable_frame_unwinders,
>>> +	     _("\
>>>    Enable one or more frame unwinder(s).\n\
>>>    Usage: maint frame-unwinder enable [-all | -name NAME | [-class] CLASS]\n\
>>>    \n\
>>> @@ -645,5 +673,7 @@ These are the meanings of the options:\n\
>>>    \t\tARCH      - Unwinders that use architecture-specific information;\n\
>>>    \n\
>>>    UNWINDER and NAME are case insensitive."),
>>> -	   &maint_frame_unwinder);
>>> +	     &maint_frame_unwinder);
>>> +  set_cmd_completer_handle_brkchars (c,
>>> +				     enable_disable_frame_unwinders_completer);
>>>    }
>>>