[2.27 COMMITTED] aarch64: Fix DT_AARCH64_VARIANT_PCS handling [BZ #26798]

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The variant PCS support was ineffective because in the common case
linkmap->l_mach.plt == 0 but then the symbol table flags were ignored
and normal lazy binding was used instead of resolving the relocs early.
(This was a misunderstanding about how GOT[1] is setup by the linker.)

In practice this mainly affects SVE calls when the vector length is
more than 128 bits, then the top bits of the argument registers get
clobbered during lazy binding.

Fixes bug 26798.

(cherry picked from commit 558251bd8785760ad40fcbfeaaee5d27fa5b0fe4)
---
 sysdeps/aarch64/dl-machine.h | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h
index 0c1f8d66b3..8989398186 100644
--- a/sysdeps/aarch64/dl-machine.h
+++ b/sysdeps/aarch64/dl-machine.h
@@ -388,13 +388,6 @@ elf_machine_lazy_rel (struct link_map *map,
   /* Check for unexpected PLT reloc type.  */
   if (__builtin_expect (r_type == AARCH64_R(JUMP_SLOT), 1))
     {
-      if (map->l_mach.plt == 0)
-       {
-         /* Prelinking.  */
-         *reloc_addr += l_addr;
-         return;
-       }
-
       if (1) /* DT_AARCH64_VARIANT_PCS is not available, so always check.  */
        {
          /* Check the symbol table for variant PCS symbols.  */
@@ -418,7 +411,10 @@ elf_machine_lazy_rel (struct link_map *map,
            }
        }

-      *reloc_addr = map->l_mach.plt;
+      if (map->l_mach.plt == 0)
+       *reloc_addr += l_addr;
+      else
+       *reloc_addr = map->l_mach.plt;
     }
   else if (__builtin_expect (r_type == AARCH64_R(TLSDESC), 1))
     {
--
2.17.1

IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.