[1/2] gdb/c++: validate 'using' directives based on the current line

  When asking GDB to print a variable from an imported namespace, we only
want to see variables imported in lines that the inferior has already
gone through, as is being tested last in gdb.cp/nsusing.exp. However
with the proposed change to gdb.cp/nsusing.exp, we get the following
failures:

(gdb) PASS: gdb.cp/nsusing.exp: continue to breakpoint: marker10 stop
print x
$9 = 911
(gdb) FAIL: gdb.cp/nsusing.exp: print x, before using statement
next
15        y += x;
(gdb) PASS: gdb.cp/nsusing.exp: using namespace M
print x
$10 = 911
(gdb) PASS: gdb.cp/nsusing.exp: print x, only using M

Showing that the feature wasn't functioning properly, it just so
happened that gcc ordered the namespaces in a convenient way.
This happens because GDB doesn't take into account the line where the
"using namespace" directive is written. So long as it shows up in the
current scope, we assume it is valid.

To fix this, add a new member to struct using_direct, that stores the
line where the directive was written, and a new function that informs if
the using directive is valid already.

Unfortunately, due to a GCC bug, the failure still shows up. Compilers
that set the declaration line of the using directive correctly (such as
Clang) do not show such a bug, so the test includes an XFAIL for gcc
code.

Finally, because the final test of gdb.cp/nsusing.exp has turned into
multiple that all would need XFAILs for older GCCs (<= 4.3), and that
GCC is very old, if it is detected, the test just exits early.
---
 gdb/cp-namespace.c               | 15 ++++++++++++---
 gdb/dwarf2/read.c                | 30 +++++++++++++++++++++++++++++-
 gdb/namespace.c                  | 26 ++++++++++++++++++++++++++
 gdb/namespace.h                  | 14 +++++++++++++-
 gdb/testsuite/gdb.cp/nsusing.cc  |  3 ++-
 gdb/testsuite/gdb.cp/nsusing.exp | 16 +++++++++++++---
 6 files changed, 95 insertions(+), 9 deletions(-)
  

>>>>> "Bruno" == Bruno Larsen via Gdb-patches <gdb-patches@sourceware.org> writes:

Bruno> When asking GDB to print a variable from an imported namespace, we only
Bruno> want to see variables imported in lines that the inferior has already
Bruno> gone through, as is being tested last in gdb.cp/nsusing.exp. However
Bruno> with the proposed change to gdb.cp/nsusing.exp, we get the following
Bruno> failures:

Thanks for the patch.  I have a few minor comments.

Bruno> +      /* If the using directive was below the place we are stopped at,
Bruno> +	 do not use this directive.  */
Bruno> +      if (!valid_line (current, boundary_sal.line))
Bruno> +	continue;

'valid_line' seems like a kind of generic name for this.
Maybe it should be a method on 'using_direct'?

Bruno> +  /* When was the using directive was declared.
Bruno> +     If this was not supplied, set it to 0 so the directive is always valid.
Bruno> +     Since the type changes from DWARF 4 to DWARF 5, we must check
Bruno> +     the type of the attribute.  */
Bruno> +  struct attribute *decl_line = dwarf2_attr (die, DW_AT_decl_line, cu);
Bruno> +  unsigned int line;
Bruno> +  if (decl_line == nullptr)
Bruno> +    line = 0;
Bruno> +  else if (decl_line->form_is_constant ())
Bruno> +    line = decl_line->constant_value (0);
Bruno> +  else if (decl_line->form_is_unsigned ())
Bruno> +    line = decl_line->as_unsigned ();
Bruno> +  else
Bruno> +    gdb_assert_not_reached ();

Asserting here seems wrong, because it means gdb will crash in response
to invalid DWARF.  It's better to emit a complaint and fall back to some
default, or ignore the directive.

Bruno>  	  std::vector<const char *> excludes;
Bruno> +	  struct attribute *decl_line = dwarf2_attr (die, DW_AT_decl_line, cu);
Bruno> +	  unsigned int line;
Bruno> +	  if (decl_line == nullptr)
Bruno> +	    line = 0;
Bruno> +	  else if (decl_line->form_is_constant ())
Bruno> +	    line = decl_line->constant_value (0);
Bruno> +	  else if (decl_line->form_is_unsigned ())
Bruno> +	    line = decl_line->as_unsigned ();
Bruno> +	  else
Bruno> +	    gdb_assert_not_reached ();

Here too.
If there's a lot of duplicated code maybe it should be factored into a
new function (I didn't look).

Bruno> +bool
Bruno> +valid_line (struct using_direct *using_dir,

Seems like this could be const; and if it's a method it could be
const-qualified.

Bruno> +      return using_dir->decl_line <= curr_sal.line
Bruno> +	     || using_dir->decl_line >= boundary;

GNU style would parenthesize this.

Bruno>    struct using_direct *next;
 
Bruno> +  unsigned int decl_line;

Should have a comment.

Tom
  

Bruno Larsen via Gdb-patches <gdb-patches@sourceware.org> writes:

> When asking GDB to print a variable from an imported namespace, we only
> want to see variables imported in lines that the inferior has already
> gone through, as is being tested last in gdb.cp/nsusing.exp. However
> with the proposed change to gdb.cp/nsusing.exp, we get the following
> failures:
>
> (gdb) PASS: gdb.cp/nsusing.exp: continue to breakpoint: marker10 stop
> print x
> $9 = 911
> (gdb) FAIL: gdb.cp/nsusing.exp: print x, before using statement
> next
> 15        y += x;
> (gdb) PASS: gdb.cp/nsusing.exp: using namespace M
> print x
> $10 = 911
> (gdb) PASS: gdb.cp/nsusing.exp: print x, only using M
>
> Showing that the feature wasn't functioning properly, it just so
> happened that gcc ordered the namespaces in a convenient way.
> This happens because GDB doesn't take into account the line where the
> "using namespace" directive is written. So long as it shows up in the
> current scope, we assume it is valid.
>
> To fix this, add a new member to struct using_direct, that stores the
> line where the directive was written, and a new function that informs if
> the using directive is valid already.
>
> Unfortunately, due to a GCC bug, the failure still shows up. Compilers
> that set the declaration line of the using directive correctly (such as
> Clang) do not show such a bug, so the test includes an XFAIL for gcc
> code.
>
> Finally, because the final test of gdb.cp/nsusing.exp has turned into
> multiple that all would need XFAILs for older GCCs (<= 4.3), and that
> GCC is very old, if it is detected, the test just exits early.
> ---
>  gdb/cp-namespace.c               | 15 ++++++++++++---
>  gdb/dwarf2/read.c                | 30 +++++++++++++++++++++++++++++-
>  gdb/namespace.c                  | 26 ++++++++++++++++++++++++++
>  gdb/namespace.h                  | 14 +++++++++++++-
>  gdb/testsuite/gdb.cp/nsusing.cc  |  3 ++-
>  gdb/testsuite/gdb.cp/nsusing.exp | 16 +++++++++++++---
>  6 files changed, 95 insertions(+), 9 deletions(-)
>
> diff --git a/gdb/cp-namespace.c b/gdb/cp-namespace.c
> index 634dab6ada0..c1b6978b7c8 100644
> --- a/gdb/cp-namespace.c
> +++ b/gdb/cp-namespace.c
> @@ -93,10 +93,12 @@ cp_scan_for_anonymous_namespaces (struct buildsym_compunit *compunit,
>  	      /* We've found a component of the name that's an
>  		 anonymous namespace.  So add symbols in it to the
>  		 namespace given by the previous component if there is
> -		 one, or to the global namespace if there isn't.  */
> +		 one, or to the global namespace if there isn't.
> +		 The declared line of this using directive can be set
> +		 to 0, this way it is always considered valid.  */
>  	      std::vector<const char *> excludes;
>  	      add_using_directive (compunit->get_local_using_directives (),
> -				   dest, src, NULL, NULL, excludes,
> +				   dest, src, NULL, NULL, excludes, 0,
>  				   1, &objfile->objfile_obstack);
>  	    }
>  	  /* The "+ 2" is for the "::".  */
> @@ -392,16 +394,23 @@ cp_lookup_symbol_via_imports (const char *scope,
>    if (sym.symbol != NULL)
>      return sym;
>  
> +  /* Due to a GCC bug, we need to know the boundaries of the current block
> +     to know if a certain using directive is valid.  */
> +  symtab_and_line boundary_sal = find_pc_line (block->end () - 1, 0);
> +
>    /* Go through the using directives.  If any of them add new names to
>       the namespace we're searching in, see if we can find a match by
>       applying them.  */
> -
>    for (current = block_using (block);
>         current != NULL;
>         current = current->next)
>      {
>        const char **excludep;
>  
> +      /* If the using directive was below the place we are stopped at,
> +	 do not use this directive.  */
> +      if (!valid_line (current, boundary_sal.line))
> +	continue;
>        len = strlen (current->import_dest);
>        directive_match = (search_parents
>  			 ? (startswith (scope, current->import_dest)
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index 071d0c48e99..7755f87f5bb 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -9435,12 +9435,28 @@ read_import_statement (struct die_info *die, struct dwarf2_cu *cu)
>  	process_die (child_die, cu);
>        }
>  
> +  /* When was the using directive was declared.
> +     If this was not supplied, set it to 0 so the directive is always valid.
> +     Since the type changes from DWARF 4 to DWARF 5, we must check
> +     the type of the attribute.  */
> +  struct attribute *decl_line = dwarf2_attr (die, DW_AT_decl_line, cu);
> +  unsigned int line;
> +  if (decl_line == nullptr)
> +    line = 0;
> +  else if (decl_line->form_is_constant ())
> +    line = decl_line->constant_value (0);
> +  else if (decl_line->form_is_unsigned ())
> +    line = decl_line->as_unsigned ();
> +  else
> +    gdb_assert_not_reached ();
> +
>    add_using_directive (using_directives (cu),
>  		       import_prefix,
>  		       canonical_name,
>  		       import_alias,
>  		       imported_declaration,
>  		       excludes,
> +		       line,
>  		       0,
>  		       &objfile->objfile_obstack);
>  }
> @@ -16064,9 +16080,21 @@ read_namespace (struct die_info *die, struct dwarf2_cu *cu)
>  	  const char *previous_prefix = determine_prefix (die, cu);
>  
>  	  std::vector<const char *> excludes;
> +	  struct attribute *decl_line = dwarf2_attr (die, DW_AT_decl_line, cu);
> +	  unsigned int line;
> +	  if (decl_line == nullptr)
> +	    line = 0;
> +	  else if (decl_line->form_is_constant ())
> +	    line = decl_line->constant_value (0);
> +	  else if (decl_line->form_is_unsigned ())
> +	    line = decl_line->as_unsigned ();
> +	  else
> +	    gdb_assert_not_reached ();
>  	  add_using_directive (using_directives (cu),
>  			       previous_prefix, type->name (), NULL,
> -			       NULL, excludes, 0, &objfile->objfile_obstack);
> +			       NULL, excludes,
> +			       line,
> +			       0, &objfile->objfile_obstack);
>  	}
>      }
>  
> diff --git a/gdb/namespace.c b/gdb/namespace.c
> index 0c39c921a3e..d467b0c80bb 100644
> --- a/gdb/namespace.c
> +++ b/gdb/namespace.c
> @@ -18,6 +18,7 @@
>  
>  #include "defs.h"
>  #include "namespace.h"
> +#include "frame.h"
>  
>  /* Add a using directive to USING_DIRECTIVES.  If the using directive
>     in question has already been added, don't add it twice.
> @@ -40,6 +41,7 @@ add_using_directive (struct using_direct **using_directives,
>  		     const char *alias,
>  		     const char *declaration,
>  		     const std::vector<const char *> &excludes,
> +		     unsigned int decl_line,
>  		     int copy_names,
>  		     struct obstack *obstack)
>  {
> @@ -76,6 +78,9 @@ add_using_directive (struct using_direct **using_directives,
>        if (ix < excludes.size () || current->excludes[ix] != NULL)
>  	continue;
>  
> +      if (decl_line != current->decl_line)
> +	continue;
> +
>        /* Parameters exactly match CURRENT.  */
>        return;
>      }
> @@ -111,6 +116,27 @@ add_using_directive (struct using_direct **using_directives,
>  	    excludes.size () * sizeof (*newobj->excludes));
>    newobj->excludes[excludes.size ()] = NULL;
>  
> +  newobj->decl_line = decl_line;
> +
>    newobj->next = *using_directives;
>    *using_directives = newobj;
>  }
> +
> +/* See namespace.h.  */
> +
> +bool
> +valid_line (struct using_direct *using_dir,
> +	    unsigned int boundary)
> +{
> +  try
> +    {
> +      CORE_ADDR curr_pc = get_frame_pc (get_selected_frame (nullptr));
> +      symtab_and_line curr_sal = find_pc_line (curr_pc, 0);
> +      return using_dir->decl_line <= curr_sal.line
> +	     || using_dir->decl_line >= boundary;
> +    }
> +  catch (const gdb_exception &ex)
> +    {
> +      return true;
> +    }
> +}
> diff --git a/gdb/namespace.h b/gdb/namespace.h
> index dc052a44e42..ed97f9cf804 100644
> --- a/gdb/namespace.h
> +++ b/gdb/namespace.h
> @@ -30,7 +30,8 @@
>     string representing the alias.  Otherwise, ALIAS is NULL.
>     DECLARATION is the name of the imported declaration, if this import
>     statement represents one.  Otherwise DECLARATION is NULL and this
> -   import statement represents a namespace.
> +   import statement represents a namespace.  DECL_LINE is the line
> +   where the using directive is written in the source code.
>  
>     C++:      using namespace A;
>     Fortran:  use A
> @@ -96,6 +97,8 @@ struct using_direct
>  
>    struct using_direct *next;
>  
> +  unsigned int decl_line;
> +
>    /* Used during import search to temporarily mark this node as
>       searched.  */
>    int searched;
> @@ -111,7 +114,16 @@ extern void add_using_directive (struct using_direct **using_directives,
>  				 const char *alias,
>  				 const char *declaration,
>  				 const std::vector<const char *> &excludes,
> +				 const unsigned int decl_line,
>  				 int copy_names,
>  				 struct obstack *obstack);
>  
> +/* Returns true if the using_direcive USING_DIR is valid in CURR_LINE.
> +   Because current GCC (at least version 12.2) sets the decl_line as
> +   the last line in the current block, we need to take this into
> +   consideration when checking the validity, by comparing it to
> +   BOUNDARY, the last line of the current block.  */
> +extern bool valid_line (struct using_direct *using_dir,
> +			unsigned int boundary);
> +
>  #endif /* NAMESPACE_H */
> diff --git a/gdb/testsuite/gdb.cp/nsusing.cc b/gdb/testsuite/gdb.cp/nsusing.cc
> index fa5c9d01f59..dcf0ba99e22 100644
> --- a/gdb/testsuite/gdb.cp/nsusing.cc
> +++ b/gdb/testsuite/gdb.cp/nsusing.cc
> @@ -10,8 +10,9 @@ namespace N
>  
>  int marker10 ()
>  {
> +  int y = 1; // marker10 stop
>    using namespace M;
> -  int y = x + 1; // marker10 stop
> +  y += x;
>    using namespace N;
>    return y;
>  }
> diff --git a/gdb/testsuite/gdb.cp/nsusing.exp b/gdb/testsuite/gdb.cp/nsusing.exp
> index 2835207a21e..bce6e30adc1 100644
> --- a/gdb/testsuite/gdb.cp/nsusing.exp
> +++ b/gdb/testsuite/gdb.cp/nsusing.exp
> @@ -120,8 +120,18 @@ gdb_continue_to_breakpoint "marker10 stop"
>  
>  if { [test_compiler_info {gcc-[0-3]-*}] ||
>       [test_compiler_info {gcc-4-[0-3]-*}]} {
> -    setup_xfail *-*-*
> +    return
>  }
>  
> -# Assert that M::x is printed and not N::x
> -gdb_test "print x" "= 911" "print x (from M::x)"
> +gdb_test_multiple "print x" "print x, before using statement" {
> +    -re -wrap "No symbol .x. in current context.*" {
> +	pass $gdb_test_name
> +    }
> +    # GCC doesn't properly set the decl_line for namespaces, so GDB believes
> +    # that the "using namespace M" line has already passed at this point.

I'm pretty sure that comments at this scope will mess up the
gdb_test_multiple.  I don't recall the details, but it's something to do
with the way we expand the blocks to build the final gdb_expect call.

I think you need to move the comment to...


> +    -re -wrap "= 911.*" {

... here.

Thanks,
Andrew

> +	xfail $gdb_test_name
> +    }
> +}
> +gdb_test "next" ".*" "using namespace M"
> +gdb_test "print x" "= 911" "print x, only using M"
> -- 
> 2.37.3