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Re: [PATCH] PR binutils/18218: bad handling of .debug_str_offsets section


H.J. Lu writes:
 > On Thu, Apr 9, 2015 at 11:03 AM, Doug Evans <dje@google.com> wrote:
 > > On Thu, Apr 9, 2015 at 10:41 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
 > >>> Even better, treat the "sec" argument to load_specific_debug_section
 > >>> as "const Elf_Internal_Shdr * sec".
 > >>> Modifying sec->sh_size to be the size of the now-uncompressed section
 > >>> is fragile and what led to this bug. Leave this data be the
 > >>> representation of what's actually on disk, and build on it, not modify
 > >>> it.
 > >>
 > >> We need to update sh_size to get readelf to work right.
 > >
 > > I don't understand.
 > > There are lots of ways to make readelf work right.
 > > Some better than others.
 > 
 > Patches are welcome.

I would have expected a more technical explanation of why
the proposed patch is ok.

How about this?

[I can imagine there's more work to do along these lines.
At least this headed in a good direction.

Ultimately, I can imagine adding a backlink from
dwarf_section to Elf_Internal_Shdr, though a more sound
proposal would need more research.]

2015-04-09  Doug Evans  <dje@google.com>

	PR binutils/18218
	* readelf.c (printable_section_name): Constify sec argument.
	(apply_relocations): Ditto.  New arg "size".  All callers updated.
	(load_specific_debug_section): Constify sec argument.
	Remove side-effect of modifying sec->sh_size.

diff --git a/binutils/readelf.c b/binutils/readelf.c
index fea372f..44ac68a 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -550,7 +550,7 @@ print_symbol (int width, const char *symbol)
    to print multibyte characters, it just interprets them as hex values.  */
 
 static const char *
-printable_section_name (Elf_Internal_Shdr * sec)
+printable_section_name (const Elf_Internal_Shdr * sec)
 {
 #define MAX_PRINT_SEC_NAME_LEN 128
   static char  sec_name_buf [MAX_PRINT_SEC_NAME_LEN + 1];
@@ -11630,11 +11630,11 @@ is_none_reloc (unsigned int reloc_type)
 
 static void
 apply_relocations (void * file,
-		   Elf_Internal_Shdr * section,
-		   unsigned char * start)
+		   const Elf_Internal_Shdr * section,
+		   unsigned char * start, bfd_size_type size)
 {
   Elf_Internal_Shdr * relsec;
-  unsigned char * end = start + section->sh_size;
+  unsigned char * end = start + size;
 
   if (elf_header.e_type != ET_REL)
     return;
@@ -11926,7 +11926,7 @@ dump_section_as_bytes (Elf_Internal_Shdr * section,
 
   if (relocate)
     {
-      apply_relocations (file, section, start);
+      apply_relocations (file, section, start, section->sh_size);
     }
   else
     {
@@ -12066,7 +12066,7 @@ uncompress_section_contents (unsigned char **buffer,
 
 static int
 load_specific_debug_section (enum dwarf_section_display_enum debug,
-			     Elf_Internal_Shdr * sec, void * file)
+			     const Elf_Internal_Shdr * sec, void * file)
 {
   struct dwarf_section * section = &debug_displays [debug].section;
   char buf [64];
@@ -12106,7 +12106,6 @@ load_specific_debug_section (enum dwarf_section_display_enum debug,
 	     and the section size if uncompress is successful.  */
 	  free (section->start);
 	  section->start = start;
-	  sec->sh_size = size;
 	}
       section->size = size;
     }
@@ -12115,7 +12114,7 @@ load_specific_debug_section (enum dwarf_section_display_enum debug,
     return 0;
 
   if (debug_displays [debug].relocate)
-    apply_relocations ((FILE *) file, sec, section->start);
+    apply_relocations ((FILE *) file, sec, section->start, section->size);
 
   return 1;
 }


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