Patchwork [3/4] Make LD_HWCAP_MASK usable for static binaries

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Submitter Siddhesh Poyarekar
Date May 25, 2017, 8:25 p.m.
Message ID <1495743960-23665-4-git-send-email-siddhesh@sourceware.org>
Download mbox | patch
Permalink /patch/20585/
State New
Headers show

Comments

Siddhesh Poyarekar - May 25, 2017, 8:25 p.m.
The LD_HWCAP_MASK environment variable was ignored in static binaries,
which is inconsistent with the behaviour of dynamically linked
binaries.  This seems to have been because of the inability of
ld_hwcap_mask being read early enough to influence anything but now
that it is in tunables, the mask is usable in static binaries as well.

This feature is important for aarch64, which relies on HWCAP_CPUID
being masked out to disable multiarch.  A sanity test on x86_64 shows
that there are no failures.  Likewise for aarch64.

	* elf/dl-hwcaps.h [HAVE_TUNABLES]: Always read hwcap_mask.
	* sysdeps/sparc/sparc32/dl-machine.h [HAVE_TUNABLES]:
	Likewise.
	* sysdeps/x86/cpu-features.c (init_cpu_features): Always set
	up hwcap and hwcap_mask.
---
 elf/dl-hwcaps.h                    | 14 +++++++-------
 sysdeps/sparc/sparc32/dl-machine.h |  2 +-
 sysdeps/x86/cpu-features.c         |  8 +++-----
 3 files changed, 11 insertions(+), 13 deletions(-)

Patch

diff --git a/elf/dl-hwcaps.h b/elf/dl-hwcaps.h
index 169ad1b..a8060d5 100644
--- a/elf/dl-hwcaps.h
+++ b/elf/dl-hwcaps.h
@@ -18,13 +18,13 @@ 
 
 #include <elf/dl-tunables.h>
 
-#ifdef SHARED
-# if HAVE_TUNABLES
-#  define GET_HWCAP_MASK() TUNABLE_GET (glibc, tune, hwcap_mask, uint64_t)
+#if HAVE_TUNABLES
+# define GET_HWCAP_MASK() TUNABLE_GET (glibc, tune, hwcap_mask, uint64_t)
+#else
+# ifdef SHARED
+#   define GET_HWCAP_MASK() GLRO(dl_hwcap_mask)
 # else
-#  define GET_HWCAP_MASK() GLRO(dl_hwcap_mask)
+/* HWCAP_MASK is ignored in static binaries when built without tunables.  */
+#  define GET_HWCAP_MASK() (0)
 # endif
-#else
-/* HWCAP_MASK is ignored in static binaries.  */
-# define GET_HWCAP_MASK() (0)
 #endif
diff --git a/sysdeps/sparc/sparc32/dl-machine.h b/sysdeps/sparc/sparc32/dl-machine.h
index f9ae133..95f6732 100644
--- a/sysdeps/sparc/sparc32/dl-machine.h
+++ b/sysdeps/sparc/sparc32/dl-machine.h
@@ -37,7 +37,7 @@  elf_machine_matches_host (const Elf32_Ehdr *ehdr)
     return 1;
   else if (ehdr->e_machine == EM_SPARC32PLUS)
     {
-#ifdef SHARED
+#if HAVE_TUNABLES || defined SHARED
       uint64_t hwcap_mask = GET_HWCAP_MASK();
       return GLRO(dl_hwcap) & hwcap_mask & HWCAP_SPARC_V9;
 #else
diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index 4fe58bf..4288001 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -312,17 +312,16 @@  no_cpuid:
   cpu_features->model = model;
   cpu_features->kind = kind;
 
-#if IS_IN (rtld)
   /* Reuse dl_platform, dl_hwcap and dl_hwcap_mask for x86.  */
   GLRO(dl_platform) = NULL;
   GLRO(dl_hwcap) = 0;
-#if !HAVE_TUNABLES
+#if !HAVE_TUNABLES && defined SHARED
   /* The glibc.tune.hwcap_mask tunable is initialized already, so no need to do
      this.  */
   GLRO(dl_hwcap_mask) = HWCAP_IMPORTANT;
 #endif
 
-# ifdef __x86_64__
+#ifdef __x86_64__
   if (cpu_features->kind == arch_kind_intel)
     {
       if (CPU_FEATURES_ARCH_P (cpu_features, AVX512F_Usable)
@@ -352,7 +351,7 @@  no_cpuid:
 	  && CPU_FEATURES_CPU_P (cpu_features, POPCNT))
 	GLRO(dl_platform) = "haswell";
     }
-# else
+#else
   if (CPU_FEATURES_CPU_P (cpu_features, SSE2))
     GLRO(dl_hwcap) |= HWCAP_X86_SSE2;
 
@@ -360,6 +359,5 @@  no_cpuid:
     GLRO(dl_platform) = "i686";
   else if (CPU_FEATURES_ARCH_P (cpu_features, I586))
     GLRO(dl_platform) = "i586";
-# endif
 #endif
 }