x86: Update _dl_tlsdesc_dynamic to preserve caller-saved registersHEADmaster

Compiler generates the following instruction sequence for GNU2 dynamic
TLS access:

	leaq	tls_var@TLSDESC(%rip), %rax
	call	*tls_var@TLSCALL(%rax)

or

	leal	tls_var@TLSDESC(%ebx), %eax
	call	*tls_var@TLSCALL(%eax)

CALL instruction is transparent to compiler which assumes all registers,
except for EFLAGS and RAX/EAX, are unchanged after CALL.  When
_dl_tlsdesc_dynamic is called, it calls __tls_get_addr on the slow
path.  __tls_get_addr is a normal function which doesn't preserve any
caller-saved registers.  _dl_tlsdesc_dynamic saved and restored integer
caller-saved registers, but didn't preserve any other caller-saved
registers.  Add _dl_tlsdesc_dynamic IFUNC functions for FNSAVE, FXSAVE,
XSAVE and XSAVEC to save and restore all caller-saved registers.  This
fixes BZ #31372.

Add GLRO(dl_x86_64_runtime_resolve) with GLRO(dl_x86_tlsdesc_dynamic)
to optimize elf_machine_runtime_setup.
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>

1 files changed, 4 insertions, 15 deletions

diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
index 6d605d0d32..ff5d45f7cb 100644
--- a/sysdeps/x86_64/dl-machine.h
+++ b/sysdeps/x86_64/dl-machine.h
@@ -71,9 +71,6 @@ elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
 			   int lazy, int profile)
 {
   Elf64_Addr *got;
-  extern void _dl_runtime_resolve_fxsave (ElfW(Word)) attribute_hidden;
-  extern void _dl_runtime_resolve_xsave (ElfW(Word)) attribute_hidden;
-  extern void _dl_runtime_resolve_xsavec (ElfW(Word)) attribute_hidden;
   extern void _dl_runtime_profile_sse (ElfW(Word)) attribute_hidden;
   extern void _dl_runtime_profile_avx (ElfW(Word)) attribute_hidden;
   extern void _dl_runtime_profile_avx512 (ElfW(Word)) attribute_hidden;
@@ -96,8 +93,6 @@ elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
       /* Identify this shared object.  */
       *(ElfW(Addr) *) (got + 1) = (ElfW(Addr)) l;
 
-      const struct cpu_features* cpu_features = __get_cpu_features ();
-
 #ifdef SHARED
       /* The got[2] entry contains the address of a function which gets
 	 called to get the address of a so far unresolved function and
@@ -107,6 +102,7 @@ elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
 	 end in this function.  */
       if (__glibc_unlikely (profile))
 	{
+	  const struct cpu_features* cpu_features = __get_cpu_features ();
 	  if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512F))
 	    *(ElfW(Addr) *) (got + 2) = (ElfW(Addr)) &_dl_runtime_profile_avx512;
 	  else if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX))
@@ -126,15 +122,8 @@ elf_machine_runtime_setup (struct link_map *l, struct r_scope_elem *scope[],
 	  /* This function will get called to fix up the GOT entry
 	     indicated by the offset on the stack, and then jump to
 	     the resolved address.  */
-	  if (MINIMUM_X86_ISA_LEVEL >= AVX_X86_ISA_LEVEL
-	      || GLRO(dl_x86_cpu_features).xsave_state_size != 0)
-	    *(ElfW(Addr) *) (got + 2)
-	      = (CPU_FEATURE_USABLE_P (cpu_features, XSAVEC)
-		 ? (ElfW(Addr)) &_dl_runtime_resolve_xsavec
-		 : (ElfW(Addr)) &_dl_runtime_resolve_xsave);
-	  else
-	    *(ElfW(Addr) *) (got + 2)
-	      = (ElfW(Addr)) &_dl_runtime_resolve_fxsave;
+	  *(ElfW(Addr) *) (got + 2)
+	    = (ElfW(Addr)) GLRO(dl_x86_64_runtime_resolve);
 	}
     }
 
@@ -383,7 +372,7 @@ and creates an unsatisfiable circular dependency.\n",
 		  {
 		    td->arg = _dl_make_tlsdesc_dynamic
 		      (sym_map, sym->st_value + reloc->r_addend);
-		    td->entry = _dl_tlsdesc_dynamic;
+		    td->entry = GLRO(dl_x86_tlsdesc_dynamic);
 		  }
 		else
 #  endif