[v2,1/3] gdb: add convenience variables around linker namespace debugging

  This commit adds 2 simple built-in convenience variables to help users
debug an inferior with multiple linker namespaces. The first is
$_active_linker_namespaces, which just counts how many namespaces have SOs
loaded onto them. The second is $_current_linker_namespace, and it tracks
which namespace does the current location in the inferior belongs to.

This commit also introduces a test ensuring that we track namespaces
correctly, and that a user can use the $_current_linker_namespace
variable to set a conditional breakpoint, while linespec changes aren't
finalized to make it more convenient.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
---
 gdb/NEWS                                     |  6 +++
 gdb/doc/gdb.texinfo                          | 12 +++++
 gdb/solib-svr4.c                             |  6 +++
 gdb/solib.c                                  | 43 +++++++++++++++
 gdb/testsuite/gdb.base/default.exp           |  2 +
 gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c |  6 +++
 gdb/testsuite/gdb.base/dlmopen-ns-ids.exp    | 55 ++++++++++++++++++++
 7 files changed, 130 insertions(+)
  

Hi Gwen,

I found two nits - see below.

Kevin

On Wed,  9 Apr 2025 17:44:25 -0300
Guinevere Larsen <guinevere@redhat.com> wrote:

> This commit adds 2 simple built-in convenience variables to help users
> debug an inferior with multiple linker namespaces. The first is
> $_active_linker_namespaces, which just counts how many namespaces have SOs
> loaded onto them. The second is $_current_linker_namespace, and it tracks
> which namespace does the current location in the inferior belongs to.

s/does/that/

> 
> This commit also introduces a test ensuring that we track namespaces
> correctly, and that a user can use the $_current_linker_namespace
> variable to set a conditional breakpoint, while linespec changes aren't
> finalized to make it more convenient.
> 
> Reviewed-By: Eli Zaretskii <eliz@gnu.org>
> ---
>  gdb/NEWS                                     |  6 +++
>  gdb/doc/gdb.texinfo                          | 12 +++++
>  gdb/solib-svr4.c                             |  6 +++
>  gdb/solib.c                                  | 43 +++++++++++++++
>  gdb/testsuite/gdb.base/default.exp           |  2 +
>  gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c |  6 +++
>  gdb/testsuite/gdb.base/dlmopen-ns-ids.exp    | 55 ++++++++++++++++++++
>  7 files changed, 130 insertions(+)
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index 99ec392d4c4..053541683f1 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -40,6 +40,12 @@
>    namespace into which the library was loaded, if more than one namespace
>    is active.
>  
> +* New built-in convenience variables $_active_linker_namespaces and
> +  $_current_linker_namespace.  These show the number of active linkage
> +  namespaces, and the namespace to which the current location belongs to.
> +  In systems that don't support linkage namespaces, these always return 1
> +  and [[0]] respectively.
> +
>  * New commands
>  
>  maintenance check psymtabs
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index b251c8e1228..2dda8abd407 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -13046,6 +13046,18 @@ variable which may be @samp{truecolor} or @samp{24bit}. Other color spaces are
>  determined by the "Co" termcap which in turn depends on the @env{TERM}
>  environment variable.
>  
> +@vindex $_active_linker_namespaces@r{, convenience variable}
> +@item $_active_linker_namespaces
> +Number of active linkage namespaces in the inferior.  In systems with no
> +support for linkage namespaces, this variable will always be set to @samp{1}.
> +
> +@vindex $_current_linker_namespace@r{, convenience variable}
> +@item $_current_linker_namespace
> +The namespace which contains the current location in the inferior.  This
> +returns GDB's internal identifier for namespaces, which is @samp{[[@var{n}]]}
> +where @var{n} is a zero-based namespace number.  In systems with no support
> +for linkage namespaces, this variable will always be set to @samp{[[0]]}.
> +
>  @end table
>  
>  @node Convenience Funs
> diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
> index 83cb389dad5..148359a0227 100644
> --- a/gdb/solib-svr4.c
> +++ b/gdb/solib-svr4.c
> @@ -451,6 +451,12 @@ svr4_maybe_add_namespace (svr4_info *info, CORE_ADDR lmid)
>      info->namespace_id.push_back (lmid);
>  
>    info->active_namespaces.insert (i);
> +
> +  /* Create or update the convenience variable "active_namespaces".
> +     It only needs to be updated here, as this only changes when a
> +     dlmopen or dlclose call happens.  */
> +  set_internalvar_integer (lookup_internalvar ("_active_linker_namespaces"),
> +			   info->active_namespaces.size ());
>  }
>  
>  /* Return whether DEBUG_BASE is the default namespace of INFO.  */
> diff --git a/gdb/solib.c b/gdb/solib.c
> index 4876f1a92ea..1ba98137f5e 100644
> --- a/gdb/solib.c
> +++ b/gdb/solib.c
> @@ -1715,6 +1715,42 @@ default_find_solib_addr (solib &so)
>    return {};
>  }
>  
> +/* Implementation of the current_linker_namespace convenience variable.
> +   This returns the GDB internal identifier of the linker namespace,
> +   for the current frame, in the form '[[<number>]]'.  If the inferior
> +   doesn't support linker namespaces, this always returns [[0]].  */
> +
> +static value *
> +current_linker_namespace_make_value (gdbarch *gdbarch, internalvar *var,
> +				     void *ignore)
> +{
> +  const solib_ops *ops = gdbarch_so_ops (gdbarch);
> +  const language_defn *lang = language_def (get_frame_language
> +					      (get_current_frame ()));
> +  std::string nsid = "[[0]]";
> +  if (ops->find_solib_ns != nullptr)
> +    {
> +      CORE_ADDR curr_pc = get_frame_pc (get_current_frame ());
> +      for (const solib &so : current_program_space->solibs ())
> +	if (solib_contains_address_p (so, curr_pc))
> +	  {
> +	    nsid = string_printf ("[[%d]]", ops->find_solib_ns (so));
> +	    break;
> +	  }
> +    }
> +
> +
> +  /* If the PC is not in an SO, or the solib_ops doesn't support
> +     linker namespaces, the inferior is in the default namespace.  */
> +  return lang->value_string (gdbarch, nsid.c_str (), nsid.length ());
> +}
> +

Please add a comment here for current_linker_namespace_funcs, below. 
This should probably be:

/* Implementation of `$_current_linker_namespace' variable.  */

(I realize that the comment for the function above could probably
apply here too, but this is how it's done in similar situations
elsewhere in the GDB sources.)

> +static const struct internalvar_funcs current_linker_namespace_funcs =
> +{
> +  current_linker_namespace_make_value,
> +  nullptr,
> +};
> +
>  void _initialize_solib ();
>  
>  void
> @@ -1727,6 +1763,13 @@ _initialize_solib ()
>    },
>      "solib");
>  
> +  /* Convenience variables for debugging linker namespaces.  These are
> +     set here, even if the solib_ops doesn't support them,
> +     for consistency.  */
> +  create_internalvar_type_lazy ("_current_linker_namespace",
> +				&current_linker_namespace_funcs, nullptr);
> +  set_internalvar_integer (lookup_internalvar ("_active_linker_namespaces"), 1);
> +
>    add_com (
>      "sharedlibrary", class_files, sharedlibrary_command,
>      _ ("Load shared object library symbols for files matching REGEXP."));
> diff --git a/gdb/testsuite/gdb.base/default.exp b/gdb/testsuite/gdb.base/default.exp
> index d4d6b208057..3abd0495387 100644
> --- a/gdb/testsuite/gdb.base/default.exp
> +++ b/gdb/testsuite/gdb.base/default.exp
> @@ -699,6 +699,8 @@ set show_conv_list \
>  	{$_gdb_minor = 1} \
>  	{$_shell_exitsignal = void} \
>  	{$_shell_exitcode = 0} \
> +	{$_active_linker_namespaces = 1} \
> +	{$_current_linker_namespace = <error: No registers.>}\
>      }
>  if [allow_python_tests] {
>      append show_conv_list \
> diff --git a/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c b/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c
> index 3bcd8196483..c7c038a08d1 100644
> --- a/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c
> +++ b/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c
> @@ -41,6 +41,12 @@ main (void)
>    handle[2] = dlmopen (LM_ID_NEWLM, DSO_NAME, RTLD_LAZY | RTLD_LOCAL);
>    assert (handle[2] != NULL);
>  
> +  for (dl = 2; dl >= 0; dl--)
> +    {
> +      fun = dlsym (handle[dl], "inc");
> +      fun (dl);
> +    }
> +
>    dlclose (handle[0]); /* TAG: first dlclose */
>    dlclose (handle[1]); /* TAG: second dlclose */
>    dlclose (handle[2]); /* TAG: third dlclose */
> diff --git a/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp b/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp
> index 03b7a527af5..8f5376fa3de 100644
> --- a/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp
> +++ b/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp
> @@ -103,4 +103,59 @@ proc test_info_shared {} {
>  	"after unloading everything"
>  }
>  
> +# Run all tests related to the linkage namespaces convenience
> +# variables, _active_namespaces and _current_namespaces.
> +proc_with_prefix test_conv_vars {} {
> +    clean_restart $::binfile
> +
> +    gdb_test "print \$_active_linker_namespaces" "1" \
> +	"1 namespace before starting inferior"
> +    gdb_test "print \$_current_linker_namespace" "No registers." \
> +	"No current namespace before starting inferior"
> +
> +    if { ![runto_main] } {
> +	return
> +    }
> +
> +    gdb_test "print \$_active_linker_namespaces" "1" \
> +	"Before activating namespaces"
> +    gdb_test "print \$_current_linker_namespace" ".*\"\\\[\\\[0\\\]\\\]\"" \
> +	"Still in the default namespace"
> +
> +    gdb_breakpoint "inc" allow-pending
> +    gdb_breakpoint [gdb_get_line_number "TAG: first dlclose"]
> +
> +    foreach_with_prefix dl {3 2 1} {
> +	gdb_continue_to_breakpoint "inc"
> +
> +	gdb_test "print \$_current_linker_namespace" ".*\"\\\[\\\[$dl\\\]\\\]\"" \
> +	    "Verify we're in namespace $dl"
> +    }
> +
> +    gdb_continue_to_breakpoint "first dlclose"
> +    gdb_test "print \$_active_linker_namespaces" "4" "all SOs loaded"
> +
> +    gdb_test "next" ".*second dlclose.*" "close one SO"
> +    gdb_test "print \$_active_linker_namespaces" "3" "one SOs unloaded"
> +    gdb_test "next" ".*third dlclose.*" "close another SO"
> +    gdb_test "print \$_active_linker_namespaces" "2" "two SOs unloaded"
> +
> +    # Restarting GDB so that we can test setting a breakpoint
> +    # using the convenience variable, while a proper bp syntax
> +    # isn't implemented for namespaces
> +    clean_restart $::binfile
> +    if {![runto_main]} {
> +	return
> +    }
> +
> +    # We need to load one SO because you can't have confitional
> +    # breakpoints and pending breakpoints at the same time with
> +    # gdb_breakpoint.
> +    gdb_test "next" ".*assert.*" "load the first SO"
> +    gdb_breakpoint "inc if \$_streq(\$_current_linker_namespace, \"\[\[2\]\]\")"
> +    gdb_continue_to_breakpoint "inc"
> +    gdb_continue_to_end "" continue 1
> +}
> +
>  test_info_shared
> +test_conv_vars
> -- 
> 2.49.0
>
  

On Sat, 12 Apr 2025 16:49:44 -0700
Kevin Buettner <kevinb@redhat.com> wrote:

> I found two nits - see below.

So... with the nits fixed:

Approved-by: Kevin Buettner <kevinb@redhat.com>