Redeclare hot external libc functions with new GCC function attribute "noplt" to allow calls to these functions to avoid the PLT. This change improves

4 files changed, 34 insertions, 10 deletions

diff --git a/README.google b/README.google
index 2c776b0a06..9c43bde83e 100644
--- a/README.google
+++ b/README.google
@@ -443,3 +443,12 @@ libio/fmemopen.c
 libio/test-fmemopen.c
   For b/22167761, backport fix buffer overflow for writes to memory buffer stream (PR18549)
   https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=7c2ce714d4e853aadbec13b920576fdfada520f1
+
+string/string.h
+math/bits/mathcalls.h
+misc/sys/cdefs.h
+  Re-declare hot libc functions with "noplt" attribute available GCC 4.9
+  onwards.  This attribute allows calls to these functions to avoid the
+  PLT and improves the performance of some of our code via better icache
+  and iTLB performance.
+  (tmsriram, google-local)
diff --git a/math/bits/mathcalls.h b/math/bits/mathcalls.h
index 4cb39e85f9..6ff3f69ed2 100644
--- a/math/bits/mathcalls.h
+++ b/math/bits/mathcalls.h
@@ -150,6 +150,7 @@ __END_NAMESPACE_C99
 
 _Mdouble_BEGIN_NAMESPACE
 /* Return X to the Y power.  */
+__attribute_noplt__
 __MATHCALL (pow,, (_Mdouble_ __x, _Mdouble_ __y));
 
 /* Return the square root of X.  */
diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index c867be7cfe..e275a689ef 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -232,6 +232,15 @@
 # define __attribute_pure__ /* Ignore */
 #endif
 
+/* GCC 4.9 onwards supports function attribute "noplt".  Calls to functions
+   declared with this attribute avoid the PLT and call them indirectly via
+   a GOT entry.  */
+#if __GNUC_PREREQ (4,9) && defined(__GOOGLE_GLIBC_NOPLT)
+# define __attribute_noplt__ __attribute__ ((noplt))
+#else
+# define __attribute_noplt__ /* Ignore */
+#endif
+
 /* This declaration tells the compiler that the value is constant.  */
 #if __GNUC_PREREQ (2,5)
 # define __attribute_const__ __attribute__ ((__const__))
diff --git a/string/string.h b/string/string.h
index b127e8d9dd..0981f892b7 100644
--- a/string/string.h
+++ b/string/string.h
@@ -44,11 +44,13 @@ __BEGIN_DECLS
 __BEGIN_NAMESPACE_STD
 /* Copy N bytes of SRC to DEST.  */
 extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
-		     size_t __n) __THROW __nonnull ((1, 2));
+		     size_t __n)
+     __THROW __attribute_noplt__  __nonnull ((1, 2));
+
 /* Copy N bytes of SRC to DEST, guaranteeing
    correct behavior for overlapping strings.  */
 extern void *memmove (void *__dest, const void *__src, size_t __n)
-     __THROW __nonnull ((1, 2));
+     __THROW __attribute_noplt__ __nonnull ((1, 2));
 __END_NAMESPACE_STD
 
 /* Copy no more than N bytes of SRC to DEST, stopping when C is found.
@@ -63,20 +65,23 @@ extern void *memccpy (void *__restrict __dest, const void *__restrict __src,
 
 __BEGIN_NAMESPACE_STD
 /* Set N bytes of S to C.  */
-extern void *memset (void *__s, int __c, size_t __n) __THROW __nonnull ((1));
+extern void *memset (void *__s, int __c, size_t __n)
+     __THROW __attribute_noplt__ __nonnull ((1));
 
 /* Compare N bytes of S1 and S2.  */
 extern int memcmp (const void *__s1, const void *__s2, size_t __n)
-     __THROW __attribute_pure__ __nonnull ((1, 2));
+     __THROW __attribute_pure__ __attribute_noplt__ __nonnull ((1, 2));
 
 /* Search N bytes of S for C.  */
 #ifdef __CORRECT_ISO_CPP_STRING_H_PROTO
 extern "C++"
 {
 extern void *memchr (void *__s, int __c, size_t __n)
-      __THROW __asm ("memchr") __attribute_pure__ __nonnull ((1));
+      __THROW __asm ("memchr") __attribute_pure__
+      __attribute_noplt__ __nonnull ((1));
 extern const void *memchr (const void *__s, int __c, size_t __n)
-      __THROW __asm ("memchr") __attribute_pure__ __nonnull ((1));
+      __THROW __asm ("memchr") __attribute_pure__
+      __attribute_noplt__ __nonnull ((1));
 
 # ifdef __OPTIMIZE__
 __extern_always_inline void *
@@ -94,7 +99,7 @@ memchr (const void *__s, int __c, size_t __n) __THROW
 }
 #else
 extern void *memchr (const void *__s, int __c, size_t __n)
-      __THROW __attribute_pure__ __nonnull ((1));
+      __THROW __attribute_pure__ __attribute_noplt__ __nonnull ((1));
 #endif
 __END_NAMESPACE_STD
 
@@ -142,10 +147,10 @@ extern char *strncat (char *__restrict __dest, const char *__restrict __src,
 
 /* Compare S1 and S2.  */
 extern int strcmp (const char *__s1, const char *__s2)
-     __THROW __attribute_pure__ __nonnull ((1, 2));
+     __THROW __attribute_pure__ __attribute_noplt__ __nonnull ((1, 2));
 /* Compare N characters of S1 and S2.  */
 extern int strncmp (const char *__s1, const char *__s2, size_t __n)
-     __THROW __attribute_pure__ __nonnull ((1, 2));
+     __THROW __attribute_pure__ __attribute_noplt__ __nonnull ((1, 2));
 
 /* Compare the collated forms of S1 and S2.  */
 extern int strcoll (const char *__s1, const char *__s2)
@@ -397,7 +402,7 @@ extern void *mempcpy (void *__restrict __dest,
 __BEGIN_NAMESPACE_STD
 /* Return the length of S.  */
 extern size_t strlen (const char *__s)
-     __THROW __attribute_pure__ __nonnull ((1));
+     __THROW __attribute_pure__ __attribute_noplt__ __nonnull ((1));
 __END_NAMESPACE_STD
 
 #ifdef	__USE_XOPEN2K8