Re: gdb: Incorrect stack unwinding if compressed debug info is used

[Vladimir Simonov <sv@sw.ru>]

[-- Attachment #1: Type: text/plain, Size: 752 bytes --]

On 02/04/2011 11:31 PM, Tom Tromey wrote:
> Vladimir>  May be just change dwarf2_read_section to return
> Vladimir>  size?
>
> I think the name is ok, but I extended the comment to try to clear up
> the semantics.
>
> I am going to check in the appended patch.  If you still think the name
> is not good, pick a better one and I will rename it.

Please see attached patch. Hope it explains what I meant under
"change dwarf2_read_section".
If such changes are not acceptable by some reason(performance?,
readability?, something else) then I'm OK with current naming.

I definitely don't insist on such changes, I just interested
in understanding gdb "coding policy". If it is difficult
to explain please ignore this mail.

Best regards
Vladimir Simonov

[-- Attachment #2: gdb-7.2-compressed-section-cleanup.patch --]
[-- Type: text/plain, Size: 3732 bytes --]

--- gdb-weekly-CVS-7.2.50.20110125/gdb/dwarf2read.c.tom	2011-02-05 14:45:40.204371900 +0300
+++ gdb-weekly-CVS-7.2.50.20110125/gdb/dwarf2read.c	2011-02-05 15:41:51.501930300 +0300
@@ -1519,9 +1519,10 @@
 
 /* Read the contents of the section SECTP from object file specified by
    OBJFILE, store info about the section into INFO.
-   If the section is compressed, uncompress it before returning.  */
+   If the section is compressed, uncompress it before returning.
+   Returns the size of data accessable via info->buffer. */
 
-static void
+static bfd_size_type
 dwarf2_read_section (struct objfile *objfile, struct dwarf2_section_info *info)
 {
   bfd *abfd = objfile->obfd;
@@ -1530,13 +1531,13 @@
   unsigned char header[4];
 
   if (info->readin)
-    return;
+    return info->size;
   info->buffer = NULL;
   info->was_mmapped = 0;
   info->readin = 1;
 
   if (dwarf2_section_empty_p (info))
-    return;
+    return info->size;
 
   /* Check if the file has a 4-byte header indicating compression.  */
   if (info->size > sizeof (header)
@@ -1548,7 +1549,7 @@
         {
           zlib_decompress_section (objfile, sectp, &info->buffer,
 				   &info->size);
-          return;
+          return info->size;
         }
     }
 
@@ -1574,7 +1575,7 @@
 #if HAVE_POSIX_MADVISE
 	  posix_madvise (retbuf, map_length, POSIX_MADV_WILLNEED);
 #endif
-	  return;
+	  return info->size;
 	}
     }
 #endif
@@ -1591,28 +1592,13 @@
   if (retbuf != NULL)
     {
       info->buffer = retbuf;
-      return;
+      return info->size;
     }
 
   if (bfd_seek (abfd, sectp->filepos, SEEK_SET) != 0
       || bfd_bread (buf, info->size, abfd) != info->size)
     error (_("Dwarf Error: Can't read DWARF data from '%s'"),
 	   bfd_get_filename (abfd));
-}
-
-/* A helper function that returns the size of a section in a safe way.
-   If you are positive that the section has been read before using the
-   size, then it is safe to refer to the dwarf2_section_info object's
-   "size" field directly.  In other cases, you must call this
-   function, because for compressed sections the size field is not set
-   correctly until the section has been read.  */
-
-static bfd_size_type
-dwarf2_section_size (struct objfile *objfile,
-		     struct dwarf2_section_info *info)
-{
-  if (!info->readin)
-    dwarf2_read_section (objfile, info);
   return info->size;
 }
 
@@ -1644,11 +1630,10 @@
   else
     gdb_assert_not_reached ("unexpected section");
 
-  dwarf2_read_section (objfile, info);
+  *sizep = dwarf2_read_section (objfile, info);
 
   *sectp = info->asection;
   *bufp = info->buffer;
-  *sizep = info->size;
 }
 
 \f
@@ -2149,8 +2134,7 @@
     sec = &dwarf2_per_objfile->types;
   else
     sec = &dwarf2_per_objfile->info;
-  dwarf2_read_section (objfile, sec);
-  buffer_size = sec->size;
+  buffer_size = dwarf2_read_section (objfile, sec);
   buffer = sec->buffer;
   info_ptr = buffer + this_cu->offset;
   beg_of_comp_unit = info_ptr;
@@ -2845,7 +2829,7 @@
 	   bfd_get_filename (abfd));
 
   if (header->abbrev_offset
-      >= dwarf2_section_size (dwarf2_per_objfile->objfile,
+      >= dwarf2_read_section (dwarf2_per_objfile->objfile,
 			      &dwarf2_per_objfile->abbrev))
     error (_("Dwarf Error: bad offset (0x%lx) in compilation unit header "
 	   "(offset 0x%lx + 6) [in module %s]"),
@@ -14413,7 +14397,7 @@
       /* ".debug_loc" may not exist at all, or the offset may be outside
 	 the section.  If so, fall through to the complaint in the
 	 other branch.  */
-      && DW_UNSND (attr) < dwarf2_section_size (dwarf2_per_objfile->objfile,
+      && DW_UNSND (attr) < dwarf2_read_section (dwarf2_per_objfile->objfile,
 						&dwarf2_per_objfile->loc))
     {
       struct dwarf2_loclist_baton *baton;