[PATCH] xcoffread.c: Fix -Werror=dangling-pointer= issue with main_subfile.

[PATCH] xcoffread.c: Fix -Werror=dangling-pointer= issue with main_subfile.

[Mark Wielaard]

GCC 13 points out that main_subfile has local function scope, but a
pointer to it is assigned to the global inclTable array subfile
element field:

In function ‘void process_linenos(CORE_ADDR, CORE_ADDR)’,
    inlined from ‘void aix_process_linenos(objfile*)’ at xcoffread.c:727:19,
    inlined from ‘void aix_process_linenos(objfile*)’ at xcoffread.c:720:1:
xcoffread.c:629:37: error: storing the address of local variable ‘main_subfile’ in ‘*inclTable.19_45 + _28._inclTable::subfile’ [-Werror=dangling-pointer=]
  629 |               inclTable[ii].subfile = &main_subfile;
      |               ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
xcoffread.c: In function ‘void aix_process_linenos(objfile*)’:
xcoffread.c:579:18: note: ‘main_subfile’ declared here
  579 |   struct subfile main_subfile;
      |                  ^~~~~~~~~~~~
xcoffread.c:496:19: note: ‘inclTable’ declared here
  496 | static InclTable *inclTable;    /* global include table */
      |                   ^~~~~~~~~

Fix this by making main_subfile file static that is allocated and
deallocated together with inclTable and allocate_include_entry and
xcoff_symfile_finish. Adjust the use of main_subfile in
process_linenos to take a pointer to the struct subfile.
---
 gdb/xcoffread.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/gdb/xcoffread.c b/gdb/xcoffread.c
index d71127b40f6..db6f2df6c0a 100644
--- a/gdb/xcoffread.c
+++ b/gdb/xcoffread.c
@@ -498,6 +498,9 @@ static int inclIndx;		/* last entry to table */
 static int inclLength;		/* table length */
 static int inclDepth;		/* nested include depth */
 
+/* subfile structure for the main compilation unit.  */
+static struct subfile *main_subfile;
+
 static void allocate_include_entry (void);
 
 static void
@@ -548,6 +551,7 @@ allocate_include_entry (void)
       inclTable = XCNEWVEC (InclTable, INITIAL_INCLUDE_TABLE_LENGTH);
       inclLength = INITIAL_INCLUDE_TABLE_LENGTH;
       inclIndx = 0;
+      main_subfile = new (struct subfile);
     }
   else if (inclIndx >= inclLength)
     {
@@ -575,9 +579,6 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
   file_ptr max_offset
     = XCOFF_DATA (this_symtab_objfile)->max_lineno_offset;
 
-  /* subfile structure for the main compilation unit.  */
-  struct subfile main_subfile;
-
   /* In the main source file, any time we see a function entry, we
      reset this variable to function's absolute starting line number.
      All the following line numbers in the function are relative to
@@ -596,7 +597,7 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
     /* All source lines were in the main source file.  None in include
        files.  */
 
-    enter_line_range (&main_subfile, offset, 0, start, end,
+    enter_line_range (main_subfile, offset, 0, start, end,
 		      &main_source_baseline);
 
   else
@@ -613,7 +614,7 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
 	  if (offset < inclTable[ii].begin)
 	    {
 	      enter_line_range
-		(&main_subfile, offset, inclTable[ii].begin - linesz,
+		(main_subfile, offset, inclTable[ii].begin - linesz,
 		 start, 0, &main_source_baseline);
 	    }
 
@@ -624,9 +625,9 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
 
 	      main_source_baseline = inclTable[ii].funStartLine;
 	      enter_line_range
-		(&main_subfile, inclTable[ii].begin, inclTable[ii].end,
+		(main_subfile, inclTable[ii].begin, inclTable[ii].end,
 		 start, 0, &main_source_baseline);
-	      inclTable[ii].subfile = &main_subfile;
+	      inclTable[ii].subfile = main_subfile;
 	    }
 	  else
 	    {
@@ -648,24 +649,24 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
 	 enter remaining lines of the main file, if any left.  */
       if (offset < max_offset + 1 - linesz)
 	{
-	  enter_line_range (&main_subfile, offset, 0, start, end,
+	  enter_line_range (main_subfile, offset, 0, start, end,
 			    &main_source_baseline);
 	}
     }
 
   /* Process main file's line numbers.  */
-  if (!main_subfile.line_vector_entries.empty ())
+  if (!main_subfile->line_vector_entries.empty ())
     {
       /* Line numbers are not necessarily ordered.  xlc compilation will
 	 put static function to the end.  */
-      arrange_linetable (main_subfile.line_vector_entries);
+      arrange_linetable (main_subfile->line_vector_entries);
     }
 
   /* Now, process included files' line numbers.  */
 
   for (int ii = 0; ii < inclIndx; ++ii)
     {
-      if (inclTable[ii].subfile != ((struct subfile *) &main_subfile)
+      if (inclTable[ii].subfile != ((struct subfile *) main_subfile)
 	  && !inclTable[ii].subfile->line_vector_entries.empty ())
 	{
 	  /* Line numbers are not necessarily ordered.  xlc compilation will
@@ -1803,6 +1804,7 @@ xcoff_symfile_finish (struct objfile *objfile)
     {
       xfree (inclTable);
       inclTable = NULL;
+      delete main_subfile;
     }
   inclIndx = inclLength = inclDepth = 0;
 }
-- 
2.31.1

Re: [PATCH] xcoffread.c: Fix -Werror=dangling-pointer= issue with main_subfile.

[Simon Marchi]

On 4/29/23 17:13, Mark Wielaard wrote:
> GCC 13 points out that main_subfile has local function scope, but a
> pointer to it is assigned to the global inclTable array subfile
> element field:
> 
> In function ‘void process_linenos(CORE_ADDR, CORE_ADDR)’,
>     inlined from ‘void aix_process_linenos(objfile*)’ at xcoffread.c:727:19,
>     inlined from ‘void aix_process_linenos(objfile*)’ at xcoffread.c:720:1:
> xcoffread.c:629:37: error: storing the address of local variable ‘main_subfile’ in ‘*inclTable.19_45 + _28._inclTable::subfile’ [-Werror=dangling-pointer=]
>   629 |               inclTable[ii].subfile = &main_subfile;
>       |               ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
> xcoffread.c: In function ‘void aix_process_linenos(objfile*)’:
> xcoffread.c:579:18: note: ‘main_subfile’ declared here
>   579 |   struct subfile main_subfile;
>       |                  ^~~~~~~~~~~~
> xcoffread.c:496:19: note: ‘inclTable’ declared here
>   496 | static InclTable *inclTable;    /* global include table */
>       |                   ^~~~~~~~~
> 
> Fix this by making main_subfile file static that is allocated and
> deallocated together with inclTable and allocate_include_entry and
> xcoff_symfile_finish. Adjust the use of main_subfile in
> process_linenos to take a pointer to the struct subfile.

I'm not familiar at all with this code, but your change looks reasonable
to me.

Some style comments:

> ---
>  gdb/xcoffread.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/gdb/xcoffread.c b/gdb/xcoffread.c
> index d71127b40f6..db6f2df6c0a 100644
> --- a/gdb/xcoffread.c
> +++ b/gdb/xcoffread.c
> @@ -498,6 +498,9 @@ static int inclIndx;		/* last entry to table */
>  static int inclLength;		/* table length */
>  static int inclDepth;		/* nested include depth */
>  
> +/* subfile structure for the main compilation unit.  */
> +static struct subfile *main_subfile;

Remove "struct".

> @@ -548,6 +551,7 @@ allocate_include_entry (void)
>        inclTable = XCNEWVEC (InclTable, INITIAL_INCLUDE_TABLE_LENGTH);
>        inclLength = INITIAL_INCLUDE_TABLE_LENGTH;
>        inclIndx = 0;
> +      main_subfile = new (struct subfile);

"new subfile" would be enough.

>    for (int ii = 0; ii < inclIndx; ++ii)
>      {
> -      if (inclTable[ii].subfile != ((struct subfile *) &main_subfile)
> +      if (inclTable[ii].subfile != ((struct subfile *) main_subfile)

Since you touch this line, I think you could remove the cast.
main_subfile is already of the right type.

Simon

Re: [PATCH] xcoffread.c: Fix -Werror=dangling-pointer= issue with main_subfile.

[Mark Wielaard]

Hi Simon,

On Mon, May 01, 2023 at 09:53:39AM -0400, Simon Marchi wrote:
> > Fix this by making main_subfile file static that is allocated and
> > deallocated together with inclTable and allocate_include_entry and
> > xcoff_symfile_finish. Adjust the use of main_subfile in
> > process_linenos to take a pointer to the struct subfile.
> 
> I'm not familiar at all with this code, but your change looks reasonable
> to me.

I am also not familiar with this code, but noticed that the
fedora-latest and suse-tumbleweed buildbots started failing when they
upgraded to GCC 13.1. The simplest solution seemed to be to give both
structures the same lifetime. I didn't see any regressions with this
fix (but don't actually know if the testsuite triggers this code).

> Some style comments:
> 
> > ---
> >  gdb/xcoffread.c | 24 +++++++++++++-----------
> >  1 file changed, 13 insertions(+), 11 deletions(-)
> > 
> > diff --git a/gdb/xcoffread.c b/gdb/xcoffread.c
> > index d71127b40f6..db6f2df6c0a 100644
> > --- a/gdb/xcoffread.c
> > +++ b/gdb/xcoffread.c
> > @@ -498,6 +498,9 @@ static int inclIndx;		/* last entry to table */
> >  static int inclLength;		/* table length */
> >  static int inclDepth;		/* nested include depth */
> >  
> > +/* subfile structure for the main compilation unit.  */
> > +static struct subfile *main_subfile;
> 
> Remove "struct".

OK.
 
> > @@ -548,6 +551,7 @@ allocate_include_entry (void)
> >        inclTable = XCNEWVEC (InclTable, INITIAL_INCLUDE_TABLE_LENGTH);
> >        inclLength = INITIAL_INCLUDE_TABLE_LENGTH;
> >        inclIndx = 0;
> > +      main_subfile = new (struct subfile);
> 
> "new subfile" would be enough.

OK.

> >    for (int ii = 0; ii < inclIndx; ++ii)
> >      {
> > -      if (inclTable[ii].subfile != ((struct subfile *) &main_subfile)
> > +      if (inclTable[ii].subfile != ((struct subfile *) main_subfile)
> 
> Since you touch this line, I think you could remove the cast.
> main_subfile is already of the right type.

Right.

Will sent v2 with those changes.

Thanks,

Mark

[PATCHv2] xcoffread.c: Fix -Werror=dangling-pointer= issue with main_subfile.

[Mark Wielaard]

GCC 13 points out that main_subfile has local function scope, but a
pointer to it is assigned to the global inclTable array subfile
element field:

In function ‘void process_linenos(CORE_ADDR, CORE_ADDR)’,
    inlined from ‘void aix_process_linenos(objfile*)’ at xcoffread.c:727:19,
    inlined from ‘void aix_process_linenos(objfile*)’ at xcoffread.c:720:1:
xcoffread.c:629:37: error: storing the address of local variable ‘main_subfile’ in ‘*inclTable.19_45 + _28._inclTable::subfile’ [-Werror=dangling-pointer=]
  629 |               inclTable[ii].subfile = &main_subfile;
      |               ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
xcoffread.c: In function ‘void aix_process_linenos(objfile*)’:
xcoffread.c:579:18: note: ‘main_subfile’ declared here
  579 |   struct subfile main_subfile;
      |                  ^~~~~~~~~~~~
xcoffread.c:496:19: note: ‘inclTable’ declared here
  496 | static InclTable *inclTable;    /* global include table */
      |                   ^~~~~~~~~

Fix this by making main_subfile file static. And allocate and
deallocated together with inclTable in allocate_include_entry and
xcoff_symfile_finish. Adjust the use of main_subfile in
process_linenos to take a pointer to the subfile.
---

v2: Removed struct. new subfile. Remove unnecessary cast.

 gdb/xcoffread.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/gdb/xcoffread.c b/gdb/xcoffread.c
index d71127b40f6..e5b8e8a69fc 100644
--- a/gdb/xcoffread.c
+++ b/gdb/xcoffread.c
@@ -498,6 +498,9 @@ static int inclIndx;		/* last entry to table */
 static int inclLength;		/* table length */
 static int inclDepth;		/* nested include depth */
 
+/* subfile structure for the main compilation unit.  */
+static subfile *main_subfile;
+
 static void allocate_include_entry (void);
 
 static void
@@ -548,6 +551,7 @@ allocate_include_entry (void)
       inclTable = XCNEWVEC (InclTable, INITIAL_INCLUDE_TABLE_LENGTH);
       inclLength = INITIAL_INCLUDE_TABLE_LENGTH;
       inclIndx = 0;
+      main_subfile = new subfile;
     }
   else if (inclIndx >= inclLength)
     {
@@ -575,9 +579,6 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
   file_ptr max_offset
     = XCOFF_DATA (this_symtab_objfile)->max_lineno_offset;
 
-  /* subfile structure for the main compilation unit.  */
-  struct subfile main_subfile;
-
   /* In the main source file, any time we see a function entry, we
      reset this variable to function's absolute starting line number.
      All the following line numbers in the function are relative to
@@ -596,7 +597,7 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
     /* All source lines were in the main source file.  None in include
        files.  */
 
-    enter_line_range (&main_subfile, offset, 0, start, end,
+    enter_line_range (main_subfile, offset, 0, start, end,
 		      &main_source_baseline);
 
   else
@@ -613,7 +614,7 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
 	  if (offset < inclTable[ii].begin)
 	    {
 	      enter_line_range
-		(&main_subfile, offset, inclTable[ii].begin - linesz,
+		(main_subfile, offset, inclTable[ii].begin - linesz,
 		 start, 0, &main_source_baseline);
 	    }
 
@@ -624,9 +625,9 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
 
 	      main_source_baseline = inclTable[ii].funStartLine;
 	      enter_line_range
-		(&main_subfile, inclTable[ii].begin, inclTable[ii].end,
+		(main_subfile, inclTable[ii].begin, inclTable[ii].end,
 		 start, 0, &main_source_baseline);
-	      inclTable[ii].subfile = &main_subfile;
+	      inclTable[ii].subfile = main_subfile;
 	    }
 	  else
 	    {
@@ -648,24 +649,24 @@ process_linenos (CORE_ADDR start, CORE_ADDR end)
 	 enter remaining lines of the main file, if any left.  */
       if (offset < max_offset + 1 - linesz)
 	{
-	  enter_line_range (&main_subfile, offset, 0, start, end,
+	  enter_line_range (main_subfile, offset, 0, start, end,
 			    &main_source_baseline);
 	}
     }
 
   /* Process main file's line numbers.  */
-  if (!main_subfile.line_vector_entries.empty ())
+  if (!main_subfile->line_vector_entries.empty ())
     {
       /* Line numbers are not necessarily ordered.  xlc compilation will
 	 put static function to the end.  */
-      arrange_linetable (main_subfile.line_vector_entries);
+      arrange_linetable (main_subfile->line_vector_entries);
     }
 
   /* Now, process included files' line numbers.  */
 
   for (int ii = 0; ii < inclIndx; ++ii)
     {
-      if (inclTable[ii].subfile != ((struct subfile *) &main_subfile)
+      if (inclTable[ii].subfile != main_subfile
 	  && !inclTable[ii].subfile->line_vector_entries.empty ())
 	{
 	  /* Line numbers are not necessarily ordered.  xlc compilation will
@@ -1803,6 +1804,7 @@ xcoff_symfile_finish (struct objfile *objfile)
     {
       xfree (inclTable);
       inclTable = NULL;
+      delete main_subfile;
     }
   inclIndx = inclLength = inclDepth = 0;
 }
-- 
2.31.1

Re: [PATCHv2] xcoffread.c: Fix -Werror=dangling-pointer= issue with main_subfile.

[Tom Tromey]

>>>>> "Mark" == Mark Wielaard <mark@klomp.org> writes:

Mark> GCC 13 points out that main_subfile has local function scope, but a
Mark> pointer to it is assigned to the global inclTable array subfile
Mark> element field:

Thanks, Mark.  This is ok.

All this code seems very bit-rotted to me.  Like, it seems to me that it
doesn't even properly handle multiple objfiles, a genuinely ancient
addition to gdb.  I wonder whether it could be removed.

Tom