aarch64: Fix DT_AARCH64_VARIANT_PCS handling [BZ #26798]

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)

diff --git a/sysdeps/aarch64/dl-machine.h b/sysdeps/aarch64/dl-machine.h
index 70b9ed39250a9fd8ab6270940f2f69a383b081a9..fde7cfd9e2ba2fef7fd60b1891a7d2ae02dd2330 100644 (file)
--- a/sysdeps/aarch64/dl-machine.h
+++ b/sysdeps/aarch64/dl-machine.h
@@ -395,13 +395,6 @@ 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 (__glibc_unlikely (map->l_info[DT_AARCH64 (VARIANT_PCS)] != NULL))
        {
          /* Check the symbol table for variant PCS symbols.  */
@@ -425,7 +418,10 @@ 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))
     {