[glibc/release/2.30/master] aarch64: Fix DT_AARCH64_VARIANT_PCS handling [BZ #26798]

[glibc/release/2.30/master] aarch64: Fix DT_AARCH64_VARIANT_PCS handling [BZ #26798]

[Szabolcs Nagy]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=61e8ae9b660d98d3a139d3dd617dea16de798f88

commit 61e8ae9b660d98d3a139d3dd617dea16de798f88
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Thu Oct 22 17:55:01 2020 +0100

    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:
---
 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 9b2e0ffdbf..69f4727331 100644
--- a/sysdeps/aarch64/dl-machine.h
+++ b/sysdeps/aarch64/dl-machine.h
@@ -391,13 +391,6 @@ 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.  */
@@ -421,7 +414,10 @@ 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))
     {