[PATCH] Add avx2 fake-capability, like tls

[Victor Rodriguez <victor.rodriguez.bahena@intel.com>]

The idea of the patch is to provide AVX2 capability to glibc, original
patch from: Dimitri John Ledkov <dimitri.j.ledkov@intel.com>.
It has been proved that the use of AVX2 improves the performance of current
numerical applications. With this patch the Linux distributions will be able to
handle AVX2 in glibc

Signed-off-by: Victor Rodriguez <victor.rodriguez.bahena@intel.com>
---
 ChangeLog       |  6 ++++++
 elf/dl-cache.c  |  6 +++++-
 elf/dl-hwcaps.c | 17 +++++++++++++++++
 elf/ldconfig.c  |  1 +
 4 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index bbda2a7f2c..8a24afa918 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2016-12-30  Victor Rodriguez  <victor.rodriguez.bahena@intel.com>
+
+	* elf/dl-cache: Define AVX platform
+	* elf/dl-hwcaps.c : Adding avx2 cap support
+	* elf/ldconfig.c : Add avx2 to hwcap_extra
+
 2016-12-31  Joseph Myers  <joseph@codesourcery.com>
 
 	* math/bits/mathcalls.h [__GLIBC_USE (IEC_60559_BFP_EXT)]
diff --git a/elf/dl-cache.c b/elf/dl-cache.c
index cfa335eb32..ae5047046d 100644
--- a/elf/dl-cache.c
+++ b/elf/dl-cache.c
@@ -259,8 +259,9 @@ _dl_load_cache_lookup (const char *name)
 	platform = 1ULL << platform;
 
 #define _DL_HWCAP_TLS_MASK (1LL << 63)
+#define _DL_HWCAP_AVX2_MASK (1LL << 62)
       uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & GLRO(dl_hwcap_mask))
-				 | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
+				 | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK | _DL_HWCAP_AVX2_MASK);
 
       /* Only accept hwcap if it's for the right platform.  */
 #define HWCAP_CHECK \
@@ -271,6 +272,9 @@ _dl_load_cache_lookup (const char *name)
       if (_DL_PLATFORMS_COUNT						      \
 	  && (lib->hwcap & _DL_HWCAP_PLATFORM) != 0			      \
 	  && (lib->hwcap & _DL_HWCAP_PLATFORM) != platform)		      \
+	continue; \
+      if (!HAS_ARCH_FEATURE (AVX2_Usable) &&			\
+	    (lib->hwcap & _DL_HWCAP_AVX2_MASK)) \
 	continue
       SEARCH_CACHE (cache_new);
     }
diff --git a/elf/dl-hwcaps.c b/elf/dl-hwcaps.c
index 6004ff264d..4e46b752e7 100644
--- a/elf/dl-hwcaps.c
+++ b/elf/dl-hwcaps.c
@@ -111,6 +111,9 @@ _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
   /* For TLS enabled builds always add 'tls'.  */
   ++cnt;
 
+  /* Add 'avx2' capability on x86_64 */
+  ++cnt;
+
   /* Create temporary data structure to generate result table.  */
   struct r_strlenpair temp[cnt];
   m = 0;
@@ -163,6 +166,20 @@ _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
   temp[m].len = 3;
   ++m;
 
+  if (HAS_ARCH_FEATURE (AVX2_Usable))
+    {
+      if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
+	_dl_debug_printf ("  adding avx2 cap support\n");
+      temp[m].str = "avx2";
+      temp[m].len = 4;
+      ++m;
+    }
+  else {
+    if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
+      _dl_debug_printf ("  not adding avx2 cap support\n");
+    --cnt;
+  }
+
   assert (m == cnt);
 
   /* Determine the total size of all strings together.  */
diff --git a/elf/ldconfig.c b/elf/ldconfig.c
index 467ca8266a..ee2121786c 100644
--- a/elf/ldconfig.c
+++ b/elf/ldconfig.c
@@ -1298,6 +1298,7 @@ main (int argc, char **argv)
      under which TLS support was optional.  The entry is no longer needed, but
      must remain for compatibility.  */
   hwcap_extra[63 - _DL_FIRST_EXTRA] = "tls";
+  hwcap_extra[62 - _DL_FIRST_EXTRA] = "avx2";
 
   set_hwcap ();
 
-- 
2.11.0