xtensa: don't emit dynamic relocation for weak undefined symbol

Resolved reference to a weak undefined symbol in PIE must not have
a dynamic relative relocation against itself, otherwise the value of a
reference will be changed from 0 to the base of executable, breaking
code like the following:

  void weak_function (void);
  if (weak_function)
    weak_function ();

This fixes tests for PR ld/22269 and a number of PIE tests in xtensa gcc
testsuite.

bfd/
2018-07-06  Max Filippov  <jcmvbkbc@gmail.com>

	* elf32-xtensa.c (elf_xtensa_allocate_dynrelocs): Don't allocate
	space for dynamic relocation for undefined weak symbol.
	(elf_xtensa_relocate_section): Don't emit R_XTENSA_RELATIVE
	relocation for undefined weak symbols.
	(shrink_dynamic_reloc_sections): Don't shrink dynamic relocation
	section for relocations against undefined weak symbols.

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 16d6daf..812b8bc 100644 (file)
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,12 @@
+2018-07-06  Max Filippov  <jcmvbkbc@gmail.com>
+
+       * elf32-xtensa.c (elf_xtensa_allocate_dynrelocs): Don't allocate
+       space for dynamic relocation for undefined weak symbol.
+       (elf_xtensa_relocate_section): Don't emit R_XTENSA_RELATIVE
+       relocation for undefined weak symbols.
+       (shrink_dynamic_reloc_sections): Don't shrink dynamic relocation
+       section for relocations against undefined weak symbols.
+
 2018-07-06  Alan Hayward  <alan.hayward@arm.com>
 
        * elf.c (elfcore_grok_aarch_sve): New function.

diff --git a/bfd/elf32-xtensa.c b/bfd/elf32-xtensa.c
index 44c1074..f7f569d 100644 (file)
--- a/bfd/elf32-xtensa.c
+++ b/bfd/elf32-xtensa.c
@@ -1437,6 +1437,10 @@ elf_xtensa_allocate_dynrelocs (struct elf_link_hash_entry *h, void *arg)
   if (! elf_xtensa_dynamic_symbol_p (h, info))
     elf_xtensa_make_sym_local (info, h);
 
+  if (! elf_xtensa_dynamic_symbol_p (h, info)
+      && h->root.type == bfd_link_hash_undefweak)
+    return TRUE;
+
   if (h->plt.refcount > 0)
     htab->elf.srelplt->size += (h->plt.refcount * sizeof (Elf32_External_Rela));
 
@@ -2777,12 +2781,16 @@ elf_xtensa_relocate_section (bfd *output_bfd,
                        }
                      unresolved_reloc = FALSE;
                    }
-                 else
+                 else if (!is_weak_undef)
                    {
                      /* Generate a RELATIVE relocation.  */
                      outrel.r_info = ELF32_R_INFO (0, R_XTENSA_RELATIVE);
                      outrel.r_addend = 0;
                    }
+                 else
+                   {
+                     continue;
+                   }
                }
 
              loc = (srel->contents
@@ -10013,7 +10021,8 @@ shrink_dynamic_reloc_sections (struct bfd_link_info *info,
 
   if ((r_type == R_XTENSA_32 || r_type == R_XTENSA_PLT)
       && (input_section->flags & SEC_ALLOC) != 0
-      && (dynamic_symbol || bfd_link_pic (info)))
+      && (dynamic_symbol || bfd_link_pic (info))
+      && (!h || h->root.type != bfd_link_hash_undefweak))
     {
       asection *srel;
       bfd_boolean is_plt = FALSE;