PR22626, invalid dynindx used for dynamic relocs against section syms

_bfd_elf_link_renumber_dynsyms is called twice by the linker.  The
first call in bfd_elf_size_dynamic_sections is just to answer the
question as to whether there are there any dynamic symbols.  The
second call in bfd_elf_size_dynsym_hash_dynstr sets the st_shndx value
that dynamic symbols will have.  strip_excluded_output_sections is
called between these two calls.  So sections seen on the first
_bfd_elf_link_renumber_dynsyms pass might differ from those seen on
the second pass.  Unfortunately, that can result in a stripped
section's dynamic symbol being assigned a dynindx on the first pass
but not corrected to the final value (of zero, ie. not dynamic) on the
second pass.  PowerPC, x86, mips, and most other targets that emit
dynamic section symbols, just test that section symbol dynindx is
non-zero before using a given section symbol in dynamic relocations.

This patch prevents _bfd_elf_link_renumber_dynsyms from setting any
section symbol dynindx on the first pass.

	PR 22626
	* elflink.c (_bfd_elf_link_renumber_dynsyms): Don't set section
	dynindx when section_sym_count is NULL.
	(bfd_elf_size_dynamic_sections): Pass NULL section_sym_count to
	preliminary _bfd_elf_link_renumber_dynsyms call.

1 files changed, 14 insertions, 8 deletions

diff --git a/bfd/elflink.c b/bfd/elflink.c
index b9597cb6e1..b3cbbbb8a6 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -917,7 +917,10 @@ _bfd_elf_link_omit_section_dynsym (bfd *output_bfd ATTRIBUTE_UNUSED,
    symbol for each output section, which come first.  Next come symbols
    which have been forced to local binding.  Then all of the back-end
    allocated local dynamic syms, followed by the rest of the global
-   symbols.  */
+   symbols.  If SECTION_SYM_COUNT is NULL, section dynindx is not set.
+   (This prevents the early call before elf_backend_init_index_section
+   and strip_excluded_output_sections setting dynindx for sections
+   that are stripped.)  */
 
 static unsigned long
 _bfd_elf_link_renumber_dynsyms (bfd *output_bfd,
@@ -925,6 +928,7 @@ _bfd_elf_link_renumber_dynsyms (bfd *output_bfd,
 				unsigned long *section_sym_count)
 {
   unsigned long dynsymcount = 0;
+  bfd_boolean do_sec = section_sym_count != NULL;
 
   if (bfd_link_pic (info)
       || elf_hash_table (info)->is_relocatable_executable)
@@ -935,11 +939,16 @@ _bfd_elf_link_renumber_dynsyms (bfd *output_bfd,
 	if ((p->flags & SEC_EXCLUDE) == 0
 	    && (p->flags & SEC_ALLOC) != 0
 	    && !(*bed->elf_backend_omit_section_dynsym) (output_bfd, info, p))
-	  elf_section_data (p)->dynindx = ++dynsymcount;
-	else
+	  {
+	    ++dynsymcount;
+	    if (do_sec)
+	      elf_section_data (p)->dynindx = dynsymcount;
+	  }
+	else if (do_sec)
 	  elf_section_data (p)->dynindx = 0;
     }
-  *section_sym_count = dynsymcount;
+  if (do_sec)
+    *section_sym_count = dynsymcount;
 
   elf_link_hash_traverse (elf_hash_table (info),
 			  elf_link_renumber_local_hash_table_dynsyms,
@@ -6831,8 +6840,6 @@ bfd_elf_size_dynamic_sections (bfd *output_bfd,
 
   if (dynobj != NULL && elf_hash_table (info)->dynamic_sections_created)
     {
-      unsigned long section_sym_count;
-
       if (elf_tdata (output_bfd)->cverdefs)
 	{
 	  unsigned int crefs = elf_tdata (output_bfd)->cverdefs;
@@ -6874,8 +6881,7 @@ bfd_elf_size_dynamic_sections (bfd *output_bfd,
 
       if ((elf_tdata (output_bfd)->cverrefs == 0
 	   && elf_tdata (output_bfd)->cverdefs == 0)
-	  || _bfd_elf_link_renumber_dynsyms (output_bfd, info,
-					     &section_sym_count) <= 1)
+	  || _bfd_elf_link_renumber_dynsyms (output_bfd, info, NULL) <= 1)
 	{
 	  asection *s;