qsort: elf_sort_sections use of target_index

Message ID 20191014061138.GF10114@bubble.grove.modra.org
State New
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Series
  • qsort: elf_sort_sections use of target_index
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Commit Message

Alan Modra Oct. 14, 2019, 6:11 a.m.
elf_sort_sections tried to ensure a stable qsort by using target_index
as the final comparison, but target_index hasn't been set by anything
at the time elf_sort_sections was run.  This patch arrange to have
target_index set.

	* elf.c (_bfd_elf_map_sections_to_segments): Init target_index
	for sections about to be sorted.
	(assign_file_positions_for_load_sections): Likewise.
	(elf_sort_sections): Don't bother optimising both TOEND case.
	* elflink.c (bfd_elf_final_link): Reset target_index.


-- 
Alan Modra
Australia Development Lab, IBM

Patch

diff --git a/bfd/elf.c b/bfd/elf.c
index cbec4269cf..314c866c3f 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -4703,6 +4703,10 @@  _bfd_elf_map_sections_to_segments (bfd *abfd, struct bfd_link_info *info)
 	{
 	  if ((s->flags & SEC_ALLOC) != 0)
 	    {
+	      /* target_index is unused until bfd_elf_final_link
+		 starts output of section symbols.  Use it to make
+		 qsort stable.  */
+	      s->target_index = i;
 	      sections[i] = s;
 	      ++i;
 	      /* A wrapping section potentially clashes with header.  */
@@ -5270,14 +5274,7 @@  elf_sort_sections (const void *arg1, const void *arg2)
 
   if (TOEND (sec1))
     {
-      if (TOEND (sec2))
-	{
-	  /* If the indices are the same, do not return 0
-	     here, but continue to try the next comparison.  */
-	  if (sec1->target_index - sec2->target_index != 0)
-	    return sec1->target_index - sec2->target_index;
-	}
-      else
+      if (!TOEND (sec2))
 	return 1;
     }
   else if (TOEND (sec2))
@@ -5479,8 +5476,12 @@  assign_file_positions_for_load_sections (bfd *abfd,
       if (m->count > 1
 	  && !(elf_elfheader (abfd)->e_type == ET_CORE
 	       && m->p_type == PT_NOTE))
-	qsort (m->sections, (size_t) m->count, sizeof (asection *),
-	       elf_sort_sections);
+	{
+	  for (i = 0; i < m->count; i++)
+	    m->sections[i]->target_index = i;
+	  qsort (m->sections, (size_t) m->count, sizeof (asection *),
+		 elf_sort_sections);
+	}
 
       /* An ELF segment (described by Elf_Internal_Phdr) may contain a
 	 number of sections with contents contributing to both p_filesz
diff --git a/bfd/elflink.c b/bfd/elflink.c
index fedaf4b5a1..bfd0f019aa 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -12048,6 +12048,10 @@  bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
 	    goto error_return;
 	}
 
+      /* _bfd_elf_compute_section_file_positions makes temporary use
+	 of target_index.  Reset it.  */
+      o->target_index = 0;
+
       /* Now, reset REL_COUNT and REL_COUNT2 so that we can use them
 	 to count upwards while actually outputting the relocations.  */
       esdo->rel.count = 0;