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GNU C Library master sources branch hjl/32bit/master created. glibc-2.22-585-gc0427e7


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The branch, hjl/32bit/master has been created
        at  c0427e7b9669789b7e2daf75ca1eac2a1d7c1582 (commit)

- Log -----------------------------------------------------------------
http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=c0427e7b9669789b7e2daf75ca1eac2a1d7c1582

commit c0427e7b9669789b7e2daf75ca1eac2a1d7c1582
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Dec 10 10:40:25 2015 -0800

    Add get_prefer_map_32bit_exec

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index d90db20..3b31e1c 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -39,6 +39,51 @@ get_common_indeces (struct cpu_features *cpu_features,
     }
 }
 
+/* Return bit_Prefer_MAP_32BIT_EXEC if entry point of dynamic executable
+   is below 4GB.  Prefer_MAP_32BIT_EXEC reduces bits available for address
+   space layout randomization (ASLR), which can be disabled by setting
+   environment variable, LD_DISABLE_PREFER_MAP_32BIT_EXEC. */
+
+static inline unsigned int
+get_prefer_map_32bit_exec (void)
+{
+#ifdef __LP64__
+  extern char **__environ attribute_hidden;
+  ElfW(auxv_t) *av = GLRO(dl_auxv);
+  if (av)
+    {
+      for (; av->a_type != AT_NULL; av++)
+	if (av->a_type == AT_ENTRY && av->a_un.a_val > 0xffffffffL)
+	  return 0;
+      for (char **current = __environ; *current != NULL; ++current)
+	if (__builtin_expect ((*current)[0] == 'L', 0)
+	    && (*current)[1] == 'D'
+	    && (*current)[2] == '_')
+	  {
+	    char *envline = &(*current)[3];
+	    size_t len = 0;
+
+	    while (envline[len] != '\0' && envline[len] != '=')
+	      ++len;
+
+	    if (envline[len] != '=')
+	      /* This is a "LD_" variable at the end of the string
+		 without a '=' character.  Ignore it since otherwise
+		 we will access invalid memory below.  */
+	      continue;
+
+	    /* Check LD_DISABLE_PREFER_MAP_32BIT_EXEC=1.  */
+	    if (len == 29
+		&& memcmp (envline, "DISABLE_PREFER_MAP_32BIT_EXEC",
+			   29) == 0)
+	      return 0;
+	  }
+      return bit_Prefer_MAP_32BIT_EXEC;
+    }
+#endif
+  return 0;
+}
+
 static inline void
 init_cpu_features (struct cpu_features *cpu_features)
 {
@@ -93,10 +138,7 @@ init_cpu_features (struct cpu_features *cpu_features)
 		 from the branch.  Set the Prefer_MAP_32BIT_EXEC bit
 		 so that mmap will try to map executable pages with
 		 MAP_32BIT first.  NB: MAP_32BIT will map to lower
-		 2GB, not lower 4GB, address.  Prefer_MAP_32BIT_EXEC
-		 reduces bits available for address space layout
-		 randomization (ASLR).  Do we need to a way to disable
-		 this optimization?  */
+		 2GB, not lower 4GB, address.  */
 #if index_Fast_Unaligned_Load != index_Prefer_PMINUB_for_stringop
 # error index_Fast_Unaligned_Load != index_Prefer_PMINUB_for_stringop
 #endif
@@ -109,7 +151,7 @@ init_cpu_features (struct cpu_features *cpu_features)
 	      cpu_features->feature[index_Fast_Unaligned_Load]
 		|= (bit_Fast_Unaligned_Load
 		    | bit_Prefer_PMINUB_for_stringop
-		    | bit_Prefer_MAP_32BIT_EXEC
+		    | get_prefer_map_32bit_exec ()
 		    | bit_Slow_SSE4_2);
 	      break;
 

http://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=d895610427ad596f1cc371907f801a6cc3899952

commit d895610427ad596f1cc371907f801a6cc3899952
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Wed Oct 21 14:44:23 2015 -0700

    Add Prefer_MAP_32BIT_EXEC for Silvermont
    
    According to Silvermont software optimization guide, for 64-bit
    applications, branch prediction performance can be negatively impacted
    when the target of a branch is more than 4GB away from the branch.  Set
    the Prefer_MAP_32BIT_EXEC bit for Silvermont so that mmap will try to
    map executable pages with MAP_32BIT first.  Also enable Silvermont
    optimizations for Knights Landing.
    
    Prefer_MAP_32BIT_EXEC only affects shared libraries, not position
    independent executable (PIE), which is loaded by kernel.
    
    Prefer_MAP_32BIT_EXEC reduces bits available for address space layout
    randomization (ASLR).  Do we need to a way to disable this optimization?
    
    On Fedora 23, this patch speeds up GCC 5 testsuite by 3%.
    
    	* sysdeps/unix/sysv/linux/x86_64/64/mmap.c: New file.
    	* sysdeps/x86/cpu-features.c (init_cpu_features): Set the
    	Prefer_MAP_32BIT_EXEC bit for Silvermont.  Enable Silvermont
    	optimizations for Knights Landing.
    	* sysdeps/x86/cpu-features.h (bit_Prefer_MAP_32BIT_EXEC): New.
    	(index_Prefer_MAP_32BIT_EXEC): Likewise.

diff --git a/sysdeps/unix/sysv/linux/x86_64/64/mmap.c b/sysdeps/unix/sysv/linux/x86_64/64/mmap.c
new file mode 100644
index 0000000..57de010
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/64/mmap.c
@@ -0,0 +1,49 @@
+/* Copyright (C) 2015 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <errno.h>
+#include <sys/syscall.h>
+#include <sysdep.h>
+#include <unistd.h>
+#include <ldsodefs.h>
+#include <cpu-features.h>
+
+__ptr_t
+__mmap (__ptr_t addr, size_t len, int prot, int flags, int fd, off_t offset)
+{
+  /* If the Prefer_MAP_32BIT_EXEC bit is set, try to map executable pages
+     with MAP_32BIT first.  */
+  if (addr == NULL
+      && (prot & PROT_EXEC) != 0
+      && HAS_ARCH_FEATURE (Prefer_MAP_32BIT_EXEC))
+    {
+      addr = (__ptr_t) INLINE_SYSCALL (mmap, 6, addr, len, prot,
+				       flags | MAP_32BIT,
+				       fd, offset);
+      if (addr != MAP_FAILED)
+	return addr;
+    }
+  return (__ptr_t) INLINE_SYSCALL (mmap, 6, addr, len, prot, flags,
+				   fd, offset);
+}
+
+weak_alias (__mmap, mmap)
+weak_alias (__mmap, mmap64)
+weak_alias (__mmap, __mmap64)
diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index fba3ef0..d90db20 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -78,22 +78,38 @@ init_cpu_features (struct cpu_features *cpu_features)
 	      cpu_features->feature[index_Slow_BSF] |= bit_Slow_BSF;
 	      break;
 
+	    case 0x57:
+	      /* Knights Landing.  Enable Silvermont optimizations.  */
+
 	    case 0x37:
 	    case 0x4a:
 	    case 0x4d:
 	    case 0x5a:
 	    case 0x5d:
-	      /* Unaligned load versions are faster than SSSE3
-		 on Silvermont.  */
+	      /* Unaligned load versions are faster than SSSE3 on
+		 Silvermont.  For 64-bit applications, branch
+		 prediction performance can be negatively impacted
+		 when the target of a branch is more than 4GB away
+		 from the branch.  Set the Prefer_MAP_32BIT_EXEC bit
+		 so that mmap will try to map executable pages with
+		 MAP_32BIT first.  NB: MAP_32BIT will map to lower
+		 2GB, not lower 4GB, address.  Prefer_MAP_32BIT_EXEC
+		 reduces bits available for address space layout
+		 randomization (ASLR).  Do we need to a way to disable
+		 this optimization?  */
 #if index_Fast_Unaligned_Load != index_Prefer_PMINUB_for_stringop
 # error index_Fast_Unaligned_Load != index_Prefer_PMINUB_for_stringop
 #endif
+#if index_Fast_Unaligned_Load != index_Prefer_MAP_32BIT_EXEC
+# error index_Fast_Unaligned_Load != index_Prefer_MAP_32BIT_EXEC
+#endif
 #if index_Fast_Unaligned_Load != index_Slow_SSE4_2
 # error index_Fast_Unaligned_Load != index_Slow_SSE4_2
 #endif
 	      cpu_features->feature[index_Fast_Unaligned_Load]
 		|= (bit_Fast_Unaligned_Load
 		    | bit_Prefer_PMINUB_for_stringop
+		    | bit_Prefer_MAP_32BIT_EXEC
 		    | bit_Slow_SSE4_2);
 	      break;
 
diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h
index 80edbee..93bee69 100644
--- a/sysdeps/x86/cpu-features.h
+++ b/sysdeps/x86/cpu-features.h
@@ -33,6 +33,7 @@
 #define bit_AVX512DQ_Usable		(1 << 13)
 #define bit_I586			(1 << 14)
 #define bit_I686			(1 << 15)
+#define bit_Prefer_MAP_32BIT_EXEC	(1 << 16)
 
 /* CPUID Feature flags.  */
 
@@ -97,6 +98,7 @@
 # define index_AVX512DQ_Usable		FEATURE_INDEX_1*FEATURE_SIZE
 # define index_I586			FEATURE_INDEX_1*FEATURE_SIZE
 # define index_I686			FEATURE_INDEX_1*FEATURE_SIZE
+# define index_Prefer_MAP_32BIT_EXEC	FEATURE_INDEX_1*FEATURE_SIZE
 
 # if defined (_LIBC) && !IS_IN (nonlib)
 #  ifdef __x86_64__
@@ -248,6 +250,7 @@ extern const struct cpu_features *__get_cpu_features (void)
 # define index_AVX512DQ_Usable		FEATURE_INDEX_1
 # define index_I586			FEATURE_INDEX_1
 # define index_I686			FEATURE_INDEX_1
+# define index_Prefer_MAP_32BIT_EXEC	FEATURE_INDEX_1
 
 #endif	/* !__ASSEMBLER__ */
 

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