gcc/gcc48-asan-speedup.patch

2013-02-15  Jakub Jelinek  <jakub@redhat.com>

	* config/i386/i386.c: Use 0x7fff8000 as asan_shadow_offset on x86_64
	linux.

	* All source files: Merge from upstream.

--- gcc/config/i386/i386.c.jj	2013-02-13 17:04:34.000000000 +0100
+++ gcc/config/i386/i386.c	2013-02-15 13:27:47.674832994 +0100
@@ -5436,7 +5436,8 @@ ix86_legitimate_combined_insn (rtx insn)
 static unsigned HOST_WIDE_INT
 ix86_asan_shadow_offset (void)
 {
-  return TARGET_LP64 ? (HOST_WIDE_INT_1 << 44)
+  return TARGET_LP64 ? (TARGET_MACHO ? (HOST_WIDE_INT_1 << 44)
+				     : HOST_WIDE_INT_C (0x7fff8000))
 		     : (HOST_WIDE_INT_1 << 29);
 }
 
--- libsanitizer/sanitizer_common/sanitizer_internal_defs.h.jj	2013-02-13 11:53:43.403336342 +0100
+++ libsanitizer/sanitizer_common/sanitizer_internal_defs.h	2013-02-15 13:24:17.410033137 +0100
@@ -29,7 +29,7 @@
 # define SANITIZER_SUPPORTS_WEAK_HOOKS 0
 #endif
 
-// __has_feature
+// GCC does not understand __has_feature
 #if !defined(__has_feature)
 # define __has_feature(x) 0
 #endif
--- libsanitizer/sanitizer_common/sanitizer_linux.cc.jj	2013-02-13 11:53:43.402336347 +0100
+++ libsanitizer/sanitizer_common/sanitizer_linux.cc	2013-02-15 13:24:17.410033137 +0100
@@ -232,6 +232,21 @@ const char *GetEnv(const char *name) {
   return 0;  // Not found.
 }
 
+#ifdef __GLIBC__
+
+extern "C" {
+  extern void *__libc_stack_end;
+}
+
+static void GetArgsAndEnv(char ***argv, char ***envp) {
+  uptr *stack_end = (uptr *)__libc_stack_end;
+  int argc = *stack_end;
+  *argv = (char**)(stack_end + 1);
+  *envp = (char**)(stack_end + argc + 2);
+}
+
+#else  // __GLIBC__
+
 static void ReadNullSepFileToArray(const char *path, char ***arr,
                                    int arr_size) {
   char *buff;
@@ -251,11 +266,17 @@ static void ReadNullSepFileToArray(const
   (*arr)[count] = 0;
 }
 
+static void GetArgsAndEnv(char ***argv, char ***envp) {
+  static const int kMaxArgv = 2000, kMaxEnvp = 2000;
+  ReadNullSepFileToArray("/proc/self/cmdline", argv, kMaxArgv);
+  ReadNullSepFileToArray("/proc/self/environ", envp, kMaxEnvp);
+}
+
+#endif  // __GLIBC__
+
 void ReExec() {
-  static const int kMaxArgv = 100, kMaxEnvp = 1000;
   char **argv, **envp;
-  ReadNullSepFileToArray("/proc/self/cmdline", &argv, kMaxArgv);
-  ReadNullSepFileToArray("/proc/self/environ", &envp, kMaxEnvp);
+  GetArgsAndEnv(&argv, &envp);
   execve(argv[0], argv, envp);
 }
 
--- libsanitizer/asan/asan_internal.h.jj	2013-02-13 11:53:44.377330938 +0100
+++ libsanitizer/asan/asan_internal.h	2013-02-15 13:24:17.412033319 +0100
@@ -52,7 +52,7 @@
 
 #define ASAN_POSIX (ASAN_LINUX || ASAN_MAC)
 
-#if __has_feature(address_sanitizer)
+#if __has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)
 # error "The AddressSanitizer run-time should not be"
         " instrumented by AddressSanitizer"
 #endif
--- libsanitizer/asan/asan_mac.cc.jj	2013-02-13 11:53:44.397330832 +0100
+++ libsanitizer/asan/asan_mac.cc	2013-02-15 13:24:17.412033319 +0100
@@ -104,7 +104,24 @@ void MaybeReexec() {
     _NSGetExecutablePath(program_name, &buf_size);
     // Ok to use setenv() since the wrappers don't depend on the value of
     // asan_inited.
-    setenv(kDyldInsertLibraries, info.dli_fname, /*overwrite*/0);
+    if (dyld_insert_libraries) {
+      // Append the runtime dylib name to the existing value of
+      // DYLD_INSERT_LIBRARIES.
+      uptr old_env_len = internal_strlen(dyld_insert_libraries);
+      uptr fname_len = internal_strlen(info.dli_fname);
+      LowLevelAllocator allocator_for_env;
+      char *new_env =
+          (char*)allocator_for_env.Allocate(old_env_len + fname_len + 2);
+      internal_strncpy(new_env, dyld_insert_libraries, old_env_len);
+      new_env[old_env_len] = ':';
+      // Copy fname_len and add a trailing zero.
+      internal_strncpy(new_env + old_env_len + 1, info.dli_fname,
+                       fname_len + 1);
+      setenv(kDyldInsertLibraries, new_env, /*overwrite*/1);
+    } else {
+      // Set DYLD_INSERT_LIBRARIES equal to the runtime dylib name.
+      setenv(kDyldInsertLibraries, info.dli_fname, /*overwrite*/0);
+    }
     if (flags()->verbosity >= 1) {
       Report("exec()-ing the program with\n");
       Report("%s=%s\n", kDyldInsertLibraries, info.dli_fname);
--- libsanitizer/asan/asan_mapping.h.jj	2013-02-13 17:04:34.680198753 +0100
+++ libsanitizer/asan/asan_mapping.h	2013-02-15 13:26:25.846301749 +0100
@@ -1,7 +1,5 @@
 //===-- asan_mapping.h ------------------------------------------*- C++ -*-===//
 //
-//                     The LLVM Compiler Infrastructure
-//
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
@@ -18,6 +16,37 @@
 
 // The full explanation of the memory mapping could be found here:
 // http://code.google.com/p/address-sanitizer/wiki/AddressSanitizerAlgorithm
+//
+// Typical shadow mapping on Linux/x86_64 with SHADOW_OFFSET == 0x00007fff8000:
+// || `[0x10007fff8000, 0x7fffffffffff]` || HighMem    ||
+// || `[0x02008fff7000, 0x10007fff7fff]` || HighShadow ||
+// || `[0x00008fff7000, 0x02008fff6fff]` || ShadowGap  ||
+// || `[0x00007fff8000, 0x00008fff6fff]` || LowShadow  ||
+// || `[0x000000000000, 0x00007fff7fff]` || LowMem     ||
+//
+// When SHADOW_OFFSET is zero (-pie):
+// || `[0x100000000000, 0x7fffffffffff]` || HighMem    ||
+// || `[0x020000000000, 0x0fffffffffff]` || HighShadow ||
+// || `[0x000000040000, 0x01ffffffffff]` || ShadowGap  ||
+//
+// Special case when something is already mapped between
+// 0x003000000000 and 0x004000000000 (e.g. when prelink is installed):
+// || `[0x10007fff8000, 0x7fffffffffff]` || HighMem    ||
+// || `[0x02008fff7000, 0x10007fff7fff]` || HighShadow ||
+// || `[0x004000000000, 0x02008fff6fff]` || ShadowGap3 ||
+// || `[0x003000000000, 0x003fffffffff]` || MidMem     ||
+// || `[0x00087fff8000, 0x002fffffffff]` || ShadowGap2 ||
+// || `[0x00067fff8000, 0x00087fff7fff]` || MidShadow  ||
+// || `[0x00008fff7000, 0x00067fff7fff]` || ShadowGap  ||
+// || `[0x00007fff8000, 0x00008fff6fff]` || LowShadow  ||
+// || `[0x000000000000, 0x00007fff7fff]` || LowMem     ||
+//
+// Default Linux/i386 mapping:
+// || `[0x40000000, 0xffffffff]` || HighMem    ||
+// || `[0x28000000, 0x3fffffff]` || HighShadow ||
+// || `[0x24000000, 0x27ffffff]` || ShadowGap  ||
+// || `[0x20000000, 0x23ffffff]` || LowShadow  ||
+// || `[0x00000000, 0x1fffffff]` || LowMem     ||
 
 #if ASAN_FLEXIBLE_MAPPING_AND_OFFSET == 1
 extern SANITIZER_INTERFACE_ATTRIBUTE uptr __asan_mapping_scale;
@@ -36,7 +65,11 @@ extern SANITIZER_INTERFACE_ATTRIBUTE upt
 #   if defined(__powerpc64__)
 #    define SHADOW_OFFSET (1ULL << 41)
 #   else
-#    define SHADOW_OFFSET (1ULL << 44)
+#    if ASAN_MAC
+#     define SHADOW_OFFSET (1ULL << 44)
+#    else
+#     define SHADOW_OFFSET 0x7fff8000ULL
+#    endif
 #   endif
 #  endif
 # endif
@@ -57,49 +90,105 @@ extern SANITIZER_INTERFACE_ATTRIBUTE upt
 #define kHighShadowBeg  MEM_TO_SHADOW(kHighMemBeg)
 #define kHighShadowEnd  MEM_TO_SHADOW(kHighMemEnd)
 
+# define kMidShadowBeg MEM_TO_SHADOW(kMidMemBeg)
+# define kMidShadowEnd MEM_TO_SHADOW(kMidMemEnd)
+
 // With the zero shadow base we can not actually map pages starting from 0.
 // This constant is somewhat arbitrary.
 #define kZeroBaseShadowStart (1 << 18)
 
 #define kShadowGapBeg   (kLowShadowEnd ? kLowShadowEnd + 1 \
                                        : kZeroBaseShadowStart)
-#define kShadowGapEnd   (kHighShadowBeg - 1)
+#define kShadowGapEnd   ((kMidMemBeg ? kMidShadowBeg : kHighShadowBeg) - 1)
+
+#define kShadowGap2Beg (kMidMemBeg ? kMidShadowEnd + 1 : 0)
+#define kShadowGap2End (kMidMemBeg ? kMidMemBeg - 1 : 0)
+
+#define kShadowGap3Beg (kMidMemBeg ? kMidMemEnd + 1 : 0)
+#define kShadowGap3End (kMidMemBeg ? kHighShadowBeg - 1 : 0)
+
+#define DO_ASAN_MAPPING_PROFILE 0  // Set to 1 to profile the functions below.
+
+#if DO_ASAN_MAPPING_PROFILE
+# define PROFILE_ASAN_MAPPING() AsanMappingProfile[__LINE__]++;
+#else
+# define PROFILE_ASAN_MAPPING()
+#endif
+
+// If 1, all shadow boundaries are constants.
+// Don't set to 1 other than for testing.
+#define ASAN_FIXED_MAPPING 0
 
 namespace __asan {
 
+extern uptr AsanMappingProfile[];
+
+#if ASAN_FIXED_MAPPING
+// Fixed mapping for 64-bit Linux. Mostly used for performance comparison
+// with non-fixed mapping. As of r175253 (Feb 2013) the performance
+// difference between fixed and non-fixed mapping is below the noise level.
+static uptr kHighMemEnd = 0x7fffffffffffULL;
+static uptr kMidMemBeg =    0x3000000000ULL;
+static uptr kMidMemEnd =    0x3fffffffffULL;
+#else
 SANITIZER_INTERFACE_ATTRIBUTE
-extern uptr kHighMemEnd;  // Initialized in __asan_init.
+extern uptr kHighMemEnd, kMidMemBeg, kMidMemEnd;  // Initialized in __asan_init.
+#endif
 
 static inline bool AddrIsInLowMem(uptr a) {
+  PROFILE_ASAN_MAPPING();
   return a < kLowMemEnd;
 }
 
 static inline bool AddrIsInLowShadow(uptr a) {
+  PROFILE_ASAN_MAPPING();
   return a >= kLowShadowBeg && a <= kLowShadowEnd;
 }
 
 static inline bool AddrIsInHighMem(uptr a) {
+  PROFILE_ASAN_MAPPING();
   return a >= kHighMemBeg && a <= kHighMemEnd;
 }
 
+static inline bool AddrIsInMidMem(uptr a) {
+  PROFILE_ASAN_MAPPING();
+  return kMidMemBeg && a >= kMidMemBeg && a <= kMidMemEnd;
+}
+
 static inline bool AddrIsInMem(uptr a) {
-  return AddrIsInLowMem(a) || AddrIsInHighMem(a);
+  PROFILE_ASAN_MAPPING();
+  return AddrIsInLowMem(a) || AddrIsInMidMem(a) || AddrIsInHighMem(a);
 }
 
 static inline uptr MemToShadow(uptr p) {
+  PROFILE_ASAN_MAPPING();
   CHECK(AddrIsInMem(p));
   return MEM_TO_SHADOW(p);
 }
 
 static inline bool AddrIsInHighShadow(uptr a) {
-  return a >= kHighShadowBeg && a <=  kHighMemEnd;
+  PROFILE_ASAN_MAPPING();
+  return a >= kHighShadowBeg && a <= kHighMemEnd;
+}
+
+static inline bool AddrIsInMidShadow(uptr a) {
+  PROFILE_ASAN_MAPPING();
+  return kMidMemBeg && a >= kMidShadowBeg && a <= kMidMemEnd;
 }
 
 static inline bool AddrIsInShadow(uptr a) {
-  return AddrIsInLowShadow(a) || AddrIsInHighShadow(a);
+  PROFILE_ASAN_MAPPING();
+  return AddrIsInLowShadow(a) || AddrIsInMidShadow(a) || AddrIsInHighShadow(a);
 }
 
 static inline bool AddrIsInShadowGap(uptr a) {
+  PROFILE_ASAN_MAPPING();
+  if (kMidMemBeg) {
+    if (a <= kShadowGapEnd)
+      return SHADOW_OFFSET == 0 || a >= kShadowGapBeg;
+    return (a >= kShadowGap2Beg && a <= kShadowGap2End) ||
+           (a >= kShadowGap3Beg && a <= kShadowGap3End);
+  }
   // In zero-based shadow mode we treat addresses near zero as addresses
   // in shadow gap as well.
   if (SHADOW_OFFSET == 0)
@@ -108,10 +197,12 @@ static inline bool AddrIsInShadowGap(upt
 }
 
 static inline bool AddrIsAlignedByGranularity(uptr a) {
+  PROFILE_ASAN_MAPPING();
   return (a & (SHADOW_GRANULARITY - 1)) == 0;
 }
 
 static inline bool AddressIsPoisoned(uptr a) {
+  PROFILE_ASAN_MAPPING();
   const uptr kAccessSize = 1;
   u8 *shadow_address = (u8*)MemToShadow(a);
   s8 shadow_value = *shadow_address;
@@ -123,6 +214,9 @@ static inline bool AddressIsPoisoned(upt
   return false;
 }
 
+// Must be after all calls to PROFILE_ASAN_MAPPING().
+static const uptr kAsanMappingProfileSize = __LINE__;
+
 }  // namespace __asan
 
 #endif  // ASAN_MAPPING_H
--- libsanitizer/asan/asan_rtl.cc.jj	2013-02-13 17:04:25.688240113 +0100
+++ libsanitizer/asan/asan_rtl.cc	2013-02-15 13:24:17.411033229 +0100
@@ -25,6 +25,8 @@
 
 namespace __asan {
 
+uptr AsanMappingProfile[kAsanMappingProfileSize];
+
 static void AsanDie() {
   static atomic_uint32_t num_calls;
   if (atomic_fetch_add(&num_calls, 1, memory_order_relaxed) != 0) {
@@ -35,8 +37,14 @@ static void AsanDie() {
     Report("Sleeping for %d second(s)\n", flags()->sleep_before_dying);
     SleepForSeconds(flags()->sleep_before_dying);
   }
-  if (flags()->unmap_shadow_on_exit)
-    UnmapOrDie((void*)kLowShadowBeg, kHighShadowEnd - kLowShadowBeg);
+  if (flags()->unmap_shadow_on_exit) {
+    if (kMidMemBeg) {
+      UnmapOrDie((void*)kLowShadowBeg, kMidMemBeg - kLowShadowBeg);
+      UnmapOrDie((void*)kMidMemEnd, kHighShadowEnd - kMidMemEnd);
+    } else {
+      UnmapOrDie((void*)kLowShadowBeg, kHighShadowEnd - kLowShadowBeg);
+    }
+  }
   if (death_callback)
     death_callback();
   if (flags()->abort_on_error)
@@ -161,7 +169,10 @@ void InitializeFlags(Flags *f, const cha
 int asan_inited;
 bool asan_init_is_running;
 void (*death_callback)(void);
-uptr kHighMemEnd;
+
+#if !ASAN_FIXED_MAPPING
+uptr kHighMemEnd, kMidMemBeg, kMidMemEnd;
+#endif
 
 // -------------------------- Misc ---------------- {{{1
 void ShowStatsAndAbort() {
@@ -259,9 +270,15 @@ static NOINLINE void force_interface_sym
 static void asan_atexit() {
   Printf("AddressSanitizer exit stats:\n");
   __asan_print_accumulated_stats();
+  // Print AsanMappingProfile.
+  for (uptr i = 0; i < kAsanMappingProfileSize; i++) {
+    if (AsanMappingProfile[i] == 0) continue;
+    Printf("asan_mapping.h:%zd -- %zd\n", i, AsanMappingProfile[i]);
+  }
 }
 
 static void InitializeHighMemEnd() {
+#if !ASAN_FIXED_MAPPING
 #if SANITIZER_WORDSIZE == 64
 # if defined(__powerpc64__)
   // FIXME:
@@ -277,6 +294,58 @@ static void InitializeHighMemEnd() {
 #else  // SANITIZER_WORDSIZE == 32
   kHighMemEnd = (1ULL << 32) - 1;  // 0xffffffff;
 #endif  // SANITIZER_WORDSIZE
+#endif  // !ASAN_FIXED_MAPPING
+}
+
+static void ProtectGap(uptr a, uptr size) {
+  CHECK_EQ(a, (uptr)Mprotect(a, size));
+}
+
+static void PrintAddressSpaceLayout() {
+  Printf("|| `[%p, %p]` || HighMem    ||\n",
+         (void*)kHighMemBeg, (void*)kHighMemEnd);
+  Printf("|| `[%p, %p]` || HighShadow ||\n",
+         (void*)kHighShadowBeg, (void*)kHighShadowEnd);
+  if (kMidMemBeg) {
+    Printf("|| `[%p, %p]` || ShadowGap3 ||\n",
+           (void*)kShadowGap3Beg, (void*)kShadowGap3End);
+    Printf("|| `[%p, %p]` || MidMem     ||\n",
+           (void*)kMidMemBeg, (void*)kMidMemEnd);
+    Printf("|| `[%p, %p]` || ShadowGap2 ||\n",
+           (void*)kShadowGap2Beg, (void*)kShadowGap2End);
+    Printf("|| `[%p, %p]` || MidShadow  ||\n",
+           (void*)kMidShadowBeg, (void*)kMidShadowEnd);
+  }
+  Printf("|| `[%p, %p]` || ShadowGap  ||\n",
+         (void*)kShadowGapBeg, (void*)kShadowGapEnd);
+  if (kLowShadowBeg) {
+    Printf("|| `[%p, %p]` || LowShadow  ||\n",
+           (void*)kLowShadowBeg, (void*)kLowShadowEnd);
+    Printf("|| `[%p, %p]` || LowMem     ||\n",
+           (void*)kLowMemBeg, (void*)kLowMemEnd);
+  }
+  Printf("MemToShadow(shadow): %p %p %p %p",
+         (void*)MEM_TO_SHADOW(kLowShadowBeg),
+         (void*)MEM_TO_SHADOW(kLowShadowEnd),
+         (void*)MEM_TO_SHADOW(kHighShadowBeg),
+         (void*)MEM_TO_SHADOW(kHighShadowEnd));
+  if (kMidMemBeg) {
+    Printf(" %p %p",
+           (void*)MEM_TO_SHADOW(kMidShadowBeg),
+           (void*)MEM_TO_SHADOW(kMidShadowEnd));
+  }
+  Printf("\n");
+  Printf("red_zone=%zu\n", (uptr)flags()->redzone);
+  Printf("malloc_context_size=%zu\n", (uptr)flags()->malloc_context_size);
+
+  Printf("SHADOW_SCALE: %zx\n", (uptr)SHADOW_SCALE);
+  Printf("SHADOW_GRANULARITY: %zx\n", (uptr)SHADOW_GRANULARITY);
+  Printf("SHADOW_OFFSET: %zx\n", (uptr)SHADOW_OFFSET);
+  CHECK(SHADOW_SCALE >= 3 && SHADOW_SCALE <= 7);
+  if (kMidMemBeg)
+    CHECK(kMidShadowBeg > kLowShadowEnd &&
+          kMidMemBeg > kMidShadowEnd &&
+          kHighShadowBeg > kMidMemEnd);
 }
 
 }  // namespace __asan
@@ -352,49 +421,48 @@ void __asan_init() {
   ReplaceSystemMalloc();
   ReplaceOperatorsNewAndDelete();
 
-  if (flags()->verbosity) {
-    Printf("|| `[%p, %p]` || HighMem    ||\n",
-           (void*)kHighMemBeg, (void*)kHighMemEnd);
-    Printf("|| `[%p, %p]` || HighShadow ||\n",
-           (void*)kHighShadowBeg, (void*)kHighShadowEnd);
-    Printf("|| `[%p, %p]` || ShadowGap  ||\n",
-           (void*)kShadowGapBeg, (void*)kShadowGapEnd);
-    Printf("|| `[%p, %p]` || LowShadow  ||\n",
-           (void*)kLowShadowBeg, (void*)kLowShadowEnd);
-    Printf("|| `[%p, %p]` || LowMem     ||\n",
-           (void*)kLowMemBeg, (void*)kLowMemEnd);
-    Printf("MemToShadow(shadow): %p %p %p %p\n",
-           (void*)MEM_TO_SHADOW(kLowShadowBeg),
-           (void*)MEM_TO_SHADOW(kLowShadowEnd),
-           (void*)MEM_TO_SHADOW(kHighShadowBeg),
-           (void*)MEM_TO_SHADOW(kHighShadowEnd));
-    Printf("red_zone=%zu\n", (uptr)flags()->redzone);
-    Printf("malloc_context_size=%zu\n", (uptr)flags()->malloc_context_size);
-
-    Printf("SHADOW_SCALE: %zx\n", (uptr)SHADOW_SCALE);
-    Printf("SHADOW_GRANULARITY: %zx\n", (uptr)SHADOW_GRANULARITY);
-    Printf("SHADOW_OFFSET: %zx\n", (uptr)SHADOW_OFFSET);
-    CHECK(SHADOW_SCALE >= 3 && SHADOW_SCALE <= 7);
+  uptr shadow_start = kLowShadowBeg;
+  if (kLowShadowBeg) shadow_start -= GetMmapGranularity();
+  uptr shadow_end = kHighShadowEnd;
+  bool full_shadow_is_available =
+      MemoryRangeIsAvailable(shadow_start, shadow_end);
+
+#if ASAN_LINUX && defined(__x86_64__) && !ASAN_FIXED_MAPPING
+  if (!full_shadow_is_available) {
+    kMidMemBeg = kLowMemEnd < 0x3000000000ULL ? 0x3000000000ULL : 0;
+    kMidMemEnd = kLowMemEnd < 0x3000000000ULL ? 0x3fffffffffULL : 0;
   }
+#endif
+
+  if (flags()->verbosity)
+    PrintAddressSpaceLayout();
 
   if (flags()->disable_core) {
     DisableCoreDumper();
   }
 
-  uptr shadow_start = kLowShadowBeg;
-  if (kLowShadowBeg > 0) shadow_start -= GetMmapGranularity();
-  uptr shadow_end = kHighShadowEnd;
-  if (MemoryRangeIsAvailable(shadow_start, shadow_end)) {
-    if (kLowShadowBeg != kLowShadowEnd) {
-      // mmap the low shadow plus at least one page.
-      ReserveShadowMemoryRange(kLowShadowBeg - GetMmapGranularity(),
-                               kLowShadowEnd);
-    }
+  if (full_shadow_is_available) {
+    // mmap the low shadow plus at least one page at the left.
+    if (kLowShadowBeg)
+      ReserveShadowMemoryRange(shadow_start, kLowShadowEnd);
+    // mmap the high shadow.
+    ReserveShadowMemoryRange(kHighShadowBeg, kHighShadowEnd);
+    // protect the gap.
+    ProtectGap(kShadowGapBeg, kShadowGapEnd - kShadowGapBeg + 1);
+  } else if (kMidMemBeg &&
+      MemoryRangeIsAvailable(shadow_start, kMidMemBeg - 1) &&
+      MemoryRangeIsAvailable(kMidMemEnd + 1, shadow_end)) {
+    CHECK(kLowShadowBeg != kLowShadowEnd);
+    // mmap the low shadow plus at least one page at the left.
+    ReserveShadowMemoryRange(shadow_start, kLowShadowEnd);
+    // mmap the mid shadow.
+    ReserveShadowMemoryRange(kMidShadowBeg, kMidShadowEnd);
     // mmap the high shadow.
     ReserveShadowMemoryRange(kHighShadowBeg, kHighShadowEnd);
-    // protect the gap
-    void *prot = Mprotect(kShadowGapBeg, kShadowGapEnd - kShadowGapBeg + 1);
-    CHECK(prot == (void*)kShadowGapBeg);
+    // protect the gaps.
+    ProtectGap(kShadowGapBeg, kShadowGapEnd - kShadowGapBeg + 1);
+    ProtectGap(kShadowGap2Beg, kShadowGap2End - kShadowGap2Beg + 1);
+    ProtectGap(kShadowGap3Beg, kShadowGap3End - kShadowGap3Beg + 1);
   } else {
     Report("Shadow memory range interleaves with an existing memory mapping. "
            "ASan cannot proceed correctly. ABORTING.\n");
--- libsanitizer/include/sanitizer/common_interface_defs.h.jj	2013-02-13 11:53:44.531330044 +0100
+++ libsanitizer/include/sanitizer/common_interface_defs.h	2013-02-15 13:24:17.403032450 +0100
@@ -14,6 +14,11 @@
 #include <stddef.h>
 #include <stdint.h>
 
+// GCC does not understand __has_feature.
+#if !defined(__has_feature)
+# define __has_feature(x) 0
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
--- libsanitizer/include/sanitizer/asan_interface.h.jj	2013-02-13 11:53:44.531330044 +0100
+++ libsanitizer/include/sanitizer/asan_interface.h	2013-02-15 13:24:17.403032450 +0100
@@ -35,8 +35,8 @@ extern "C" {
   // (un)poison memory in the same memory region simultaneously.
   void __asan_unpoison_memory_region(void const volatile *addr, size_t size);
 
-  // User code should use macro instead of functions.
-#if __has_feature(address_sanitizer)
+// User code should use macros instead of functions.
+#if __has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)
 #define ASAN_POISON_MEMORY_REGION(addr, size) \
   __asan_poison_memory_region((addr), (size))
 #define ASAN_UNPOISON_MEMORY_REGION(addr, size) \