lib/asan/asan_mac.cc - native_client/pnacl-compiler-rt - Git at Google

 //===-- asan_mac.cc -------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file is a part of AddressSanitizer, an address sanity checker.
 //
 // Mac-specific details.
 //===----------------------------------------------------------------------===//

 #include "sanitizer_common/sanitizer_platform.h"
 #if SANITIZER_MAC

 #include "asan_interceptors.h"
 #include "asan_internal.h"
 #include "asan_mapping.h"
 #include "asan_stack.h"
 #include "asan_thread.h"
 #include "sanitizer_common/sanitizer_atomic.h"
 #include "sanitizer_common/sanitizer_libc.h"
 #include "sanitizer_common/sanitizer_mac.h"

 #include <crt_externs.h>  // for _NSGetArgv
 #include <dlfcn.h>  // for dladdr()
 #include <mach-o/dyld.h>
 #include <mach-o/loader.h>
 #include <sys/mman.h>
 #include <sys/resource.h>
 #include <sys/sysctl.h>
 #include <sys/ucontext.h>
 #include <fcntl.h>
 #include <pthread.h>
 #include <stdlib.h>  // for free()
 #include <unistd.h>
 #include <libkern/OSAtomic.h>

 namespace __asan {

 void InitializePlatformInterceptors() {}

 bool PlatformHasDifferentMemcpyAndMemmove() {
   // On OS X 10.7 memcpy() and memmove() are both resolved
   // into memmove$VARIANT$sse42.
   // See also http://code.google.com/p/address-sanitizer/issues/detail?id=34.
   // TODO(glider): need to check dynamically that memcpy() and memmove() are
   // actually the same function.
   return GetMacosVersion() == MACOS_VERSION_SNOW_LEOPARD;
 }

 extern "C"
 void __asan_init();

 static const char kDyldInsertLibraries[] = "DYLD_INSERT_LIBRARIES";
 LowLevelAllocator allocator_for_env;

 // Change the value of the env var |name|, leaking the original value.
 // If |name_value| is NULL, the variable is deleted from the environment,
 // otherwise the corresponding "NAME=value" string is replaced with
 // |name_value|.
 void LeakyResetEnv(const char *name, const char *name_value) {
   char ***env_ptr = _NSGetEnviron();
   CHECK(env_ptr);
   char **environ = *env_ptr;
   CHECK(environ);
   uptr name_len = internal_strlen(name);
   while (*environ != 0) {
     uptr len = internal_strlen(*environ);
     if (len > name_len) {
       const char *p = *environ;
       if (!internal_memcmp(p, name, name_len) && p[name_len] == '=') {
         // Match.
         if (name_value) {
           // Replace the old value with the new one.
           *environ = const_cast<char*>(name_value);
         } else {
           // Shift the subsequent pointers back.
           char **del = environ;
           do {
             del[0] = del[1];
           } while (*del++);
         }
       }
     }
     environ++;
   }
 }

 static bool reexec_disabled = false;

 void DisableReexec() {
   reexec_disabled = true;
 }

 void MaybeReexec() {
   if (reexec_disabled) return;

   // Make sure the dynamic ASan runtime library is preloaded so that the
   // wrappers work. If it is not, set DYLD_INSERT_LIBRARIES and re-exec
   // ourselves.
   Dl_info info;
   CHECK(dladdr((void*)((uptr)__asan_init), &info));
   char *dyld_insert_libraries =
       const_cast<char*>(GetEnv(kDyldInsertLibraries));
   uptr old_env_len = dyld_insert_libraries ?
       internal_strlen(dyld_insert_libraries) : 0;
   uptr fname_len = internal_strlen(info.dli_fname);
   const char *dylib_name = StripModuleName(info.dli_fname);
   uptr dylib_name_len = internal_strlen(dylib_name);
   if (!dyld_insert_libraries ||
       !REAL(strstr)(dyld_insert_libraries, dylib_name)) {
     // DYLD_INSERT_LIBRARIES is not set or does not contain the runtime
     // library.
     char program_name[1024];
     uint32_t buf_size = sizeof(program_name);
     _NSGetExecutablePath(program_name, &buf_size);
     char *new_env = const_cast<char*>(info.dli_fname);
     if (dyld_insert_libraries) {
       // Append the runtime dylib name to the existing value of
       // DYLD_INSERT_LIBRARIES.
       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);
       // Ok to use setenv() since the wrappers don't depend on the value of
       // asan_inited.
       setenv(kDyldInsertLibraries, new_env, /*overwrite*/1);
     } else {
       // Set DYLD_INSERT_LIBRARIES equal to the runtime dylib name.
       setenv(kDyldInsertLibraries, info.dli_fname, /*overwrite*/0);
     }
     VReport(1, "exec()-ing the program with\n");
     VReport(1, "%s=%s\n", kDyldInsertLibraries, new_env);
     VReport(1, "to enable ASan wrappers.\n");
     execv(program_name, *_NSGetArgv());

     // We get here only if execv() failed.
     Report("ERROR: The process is launched without DYLD_INSERT_LIBRARIES, "
            "which is required for ASan to work. ASan tried to set the "
            "environment variable and re-execute itself, but execv() failed, "
            "possibly because of sandbox restrictions. Make sure to launch the "
            "executable with:\n%s=%s\n", kDyldInsertLibraries, new_env);
     CHECK("execv failed" && 0);
   }

   // DYLD_INSERT_LIBRARIES is set and contains the runtime library. Let's remove
   // the dylib from the environment variable, because interceptors are installed
   // and we don't want our children to inherit the variable.

   uptr env_name_len = internal_strlen(kDyldInsertLibraries);
   // Allocate memory to hold the previous env var name, its value, the '='
   // sign and the '\0' char.
   char *new_env = (char*)allocator_for_env.Allocate(
       old_env_len + 2 + env_name_len);
   CHECK(new_env);
   internal_memset(new_env, '\0', old_env_len + 2 + env_name_len);
   internal_strncpy(new_env, kDyldInsertLibraries, env_name_len);
   new_env[env_name_len] = '=';
   char *new_env_pos = new_env + env_name_len + 1;

   // Iterate over colon-separated pieces of |dyld_insert_libraries|.
   char *piece_start = dyld_insert_libraries;
   char *piece_end = NULL;
   char *old_env_end = dyld_insert_libraries + old_env_len;
   do {
     if (piece_start[0] == ':') piece_start++;
     piece_end = REAL(strchr)(piece_start, ':');
     if (!piece_end) piece_end = dyld_insert_libraries + old_env_len;
     if ((uptr)(piece_start - dyld_insert_libraries) > old_env_len) break;
     uptr piece_len = piece_end - piece_start;

     char *filename_start =
         (char *)internal_memrchr(piece_start, '/', piece_len);
     uptr filename_len = piece_len;
     if (filename_start) {
       filename_start += 1;
       filename_len = piece_len - (filename_start - piece_start);
     } else {
       filename_start = piece_start;
     }

     // If the current piece isn't the runtime library name,
     // append it to new_env.
     if ((dylib_name_len != filename_len) ||
         (internal_memcmp(filename_start, dylib_name, dylib_name_len) != 0)) {
       if (new_env_pos != new_env + env_name_len + 1) {
         new_env_pos[0] = ':';
         new_env_pos++;
       }
       internal_strncpy(new_env_pos, piece_start, piece_len);
       new_env_pos += piece_len;
     }
     // Move on to the next piece.
     piece_start = piece_end;
   } while (piece_start < old_env_end);

   // Can't use setenv() here, because it requires the allocator to be
   // initialized.
   // FIXME: instead of filtering DYLD_INSERT_LIBRARIES here, do it in
   // a separate function called after InitializeAllocator().
   if (new_env_pos == new_env + env_name_len + 1) new_env = NULL;
   LeakyResetEnv(kDyldInsertLibraries, new_env);
 }

 // No-op. Mac does not support static linkage anyway.
 void *AsanDoesNotSupportStaticLinkage() {
   return 0;
 }

 // No-op. Mac does not support static linkage anyway.
 void AsanCheckDynamicRTPrereqs() {}

 // No-op. Mac does not support static linkage anyway.
 void AsanCheckIncompatibleRT() {}

 void AsanPlatformThreadInit() {
 }

 void ReadContextStack(void *context, uptr *stack, uptr *ssize) {
   UNIMPLEMENTED();
 }

 // Support for the following functions from libdispatch on Mac OS:
 //   dispatch_async_f()
 //   dispatch_async()
 //   dispatch_sync_f()
 //   dispatch_sync()
 //   dispatch_after_f()
 //   dispatch_after()
 //   dispatch_group_async_f()
 //   dispatch_group_async()
 // TODO(glider): libdispatch API contains other functions that we don't support
 // yet.
 //
 // dispatch_sync() and dispatch_sync_f() are synchronous, although chances are
 // they can cause jobs to run on a thread different from the current one.
 // TODO(glider): if so, we need a test for this (otherwise we should remove
 // them).
 //
 // The following functions use dispatch_barrier_async_f() (which isn't a library
 // function but is exported) and are thus supported:
 //   dispatch_source_set_cancel_handler_f()
 //   dispatch_source_set_cancel_handler()
 //   dispatch_source_set_event_handler_f()
 //   dispatch_source_set_event_handler()
 //
 // The reference manual for Grand Central Dispatch is available at
 //   http://developer.apple.com/library/mac/#documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html
 // The implementation details are at
 //   http://libdispatch.macosforge.org/trac/browser/trunk/src/queue.c

 typedef void* dispatch_group_t;
 typedef void* dispatch_queue_t;
 typedef void* dispatch_source_t;
 typedef u64 dispatch_time_t;
 typedef void (*dispatch_function_t)(void *block);
 typedef void* (*worker_t)(void *block);

 // A wrapper for the ObjC blocks used to support libdispatch.
 typedef struct {
   void *block;
   dispatch_function_t func;
   u32 parent_tid;
 } asan_block_context_t;

 ALWAYS_INLINE
 void asan_register_worker_thread(int parent_tid, StackTrace *stack) {
   AsanThread *t = GetCurrentThread();
   if (!t) {
     t = AsanThread::Create(/* start_routine */ nullptr, /* arg */ nullptr,
                            parent_tid, stack, /* detached */ true);
     t->Init();
     asanThreadRegistry().StartThread(t->tid(), 0, 0);
     SetCurrentThread(t);
   }
 }

 // For use by only those functions that allocated the context via
 // alloc_asan_context().
 extern "C"
 void asan_dispatch_call_block_and_release(void *block) {
   GET_STACK_TRACE_THREAD;
   asan_block_context_t *context = (asan_block_context_t*)block;
   VReport(2,
           "asan_dispatch_call_block_and_release(): "
           "context: %p, pthread_self: %p\n",
           block, pthread_self());
   asan_register_worker_thread(context->parent_tid, &stack);
   // Call the original dispatcher for the block.
   context->func(context->block);
   asan_free(context, &stack, FROM_MALLOC);
 }

 }  // namespace __asan

 using namespace __asan;  // NOLINT

 // Wrap |ctxt| and |func| into an asan_block_context_t.
 // The caller retains control of the allocated context.
 extern "C"
 asan_block_context_t *alloc_asan_context(void *ctxt, dispatch_function_t func,
                                          BufferedStackTrace *stack) {
   asan_block_context_t *asan_ctxt =
       (asan_block_context_t*) asan_malloc(sizeof(asan_block_context_t), stack);
   asan_ctxt->block = ctxt;
   asan_ctxt->func = func;
   asan_ctxt->parent_tid = GetCurrentTidOrInvalid();
   return asan_ctxt;
 }

 // Define interceptor for dispatch_*_f function with the three most common
 // parameters: dispatch_queue_t, context, dispatch_function_t.
 #define INTERCEPT_DISPATCH_X_F_3(dispatch_x_f)                                \
   INTERCEPTOR(void, dispatch_x_f, dispatch_queue_t dq, void *ctxt,            \
                                   dispatch_function_t func) {                 \
     GET_STACK_TRACE_THREAD;                                                   \
     asan_block_context_t *asan_ctxt = alloc_asan_context(ctxt, func, &stack); \
     if (Verbosity() >= 2) {                                     \
       Report(#dispatch_x_f "(): context: %p, pthread_self: %p\n",             \
              asan_ctxt, pthread_self());                                      \
       PRINT_CURRENT_STACK();                                                  \
     }                                                                         \
     return REAL(dispatch_x_f)(dq, (void*)asan_ctxt,                           \
                               asan_dispatch_call_block_and_release);          \
   }

 INTERCEPT_DISPATCH_X_F_3(dispatch_async_f)
 INTERCEPT_DISPATCH_X_F_3(dispatch_sync_f)
 INTERCEPT_DISPATCH_X_F_3(dispatch_barrier_async_f)

 INTERCEPTOR(void, dispatch_after_f, dispatch_time_t when,
                                     dispatch_queue_t dq, void *ctxt,
                                     dispatch_function_t func) {
   GET_STACK_TRACE_THREAD;
   asan_block_context_t *asan_ctxt = alloc_asan_context(ctxt, func, &stack);
   if (Verbosity() >= 2) {
     Report("dispatch_after_f: %p\n", asan_ctxt);
     PRINT_CURRENT_STACK();
   }
   return REAL(dispatch_after_f)(when, dq, (void*)asan_ctxt,
                                 asan_dispatch_call_block_and_release);
 }

 INTERCEPTOR(void, dispatch_group_async_f, dispatch_group_t group,
                                           dispatch_queue_t dq, void *ctxt,
                                           dispatch_function_t func) {
   GET_STACK_TRACE_THREAD;
   asan_block_context_t *asan_ctxt = alloc_asan_context(ctxt, func, &stack);
   if (Verbosity() >= 2) {
     Report("dispatch_group_async_f(): context: %p, pthread_self: %p\n",
            asan_ctxt, pthread_self());
     PRINT_CURRENT_STACK();
   }
   REAL(dispatch_group_async_f)(group, dq, (void*)asan_ctxt,
                                asan_dispatch_call_block_and_release);
 }

 #if !defined(MISSING_BLOCKS_SUPPORT)
 extern "C" {
 void dispatch_async(dispatch_queue_t dq, void(^work)(void));
 void dispatch_group_async(dispatch_group_t dg, dispatch_queue_t dq,
                           void(^work)(void));
 void dispatch_after(dispatch_time_t when, dispatch_queue_t queue,
                     void(^work)(void));
 void dispatch_source_set_cancel_handler(dispatch_source_t ds,
                                         void(^work)(void));
 void dispatch_source_set_event_handler(dispatch_source_t ds, void(^work)(void));
 }

 #define GET_ASAN_BLOCK(work) \
   void (^asan_block)(void);  \
   int parent_tid = GetCurrentTidOrInvalid(); \
   asan_block = ^(void) { \
     GET_STACK_TRACE_THREAD; \
     asan_register_worker_thread(parent_tid, &stack); \
     work(); \
   }

 INTERCEPTOR(void, dispatch_async,
             dispatch_queue_t dq, void(^work)(void)) {
   ENABLE_FRAME_POINTER;
   GET_ASAN_BLOCK(work);
   REAL(dispatch_async)(dq, asan_block);
 }

 INTERCEPTOR(void, dispatch_group_async,
             dispatch_group_t dg, dispatch_queue_t dq, void(^work)(void)) {
   ENABLE_FRAME_POINTER;
   GET_ASAN_BLOCK(work);
   REAL(dispatch_group_async)(dg, dq, asan_block);
 }

 INTERCEPTOR(void, dispatch_after,
             dispatch_time_t when, dispatch_queue_t queue, void(^work)(void)) {
   ENABLE_FRAME_POINTER;
   GET_ASAN_BLOCK(work);
   REAL(dispatch_after)(when, queue, asan_block);
 }

 INTERCEPTOR(void, dispatch_source_set_cancel_handler,
             dispatch_source_t ds, void(^work)(void)) {
   if (!work) {
     REAL(dispatch_source_set_cancel_handler)(ds, work);
     return;
   }
   ENABLE_FRAME_POINTER;
   GET_ASAN_BLOCK(work);
   REAL(dispatch_source_set_cancel_handler)(ds, asan_block);
 }

 INTERCEPTOR(void, dispatch_source_set_event_handler,
             dispatch_source_t ds, void(^work)(void)) {
   ENABLE_FRAME_POINTER;
   GET_ASAN_BLOCK(work);
   REAL(dispatch_source_set_event_handler)(ds, asan_block);
 }
 #endif

 #endif  // SANITIZER_MAC
	//===-- asan_mac.cc -------------------------------------------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This file is a part of AddressSanitizer, an address sanity checker.
	//
	// Mac-specific details.
	//===----------------------------------------------------------------------===//

	#include "sanitizer_common/sanitizer_platform.h"
	#if SANITIZER_MAC

	#include "asan_interceptors.h"
	#include "asan_internal.h"
	#include "asan_mapping.h"
	#include "asan_stack.h"
	#include "asan_thread.h"
	#include "sanitizer_common/sanitizer_atomic.h"
	#include "sanitizer_common/sanitizer_libc.h"
	#include "sanitizer_common/sanitizer_mac.h"

	#include <crt_externs.h> // for _NSGetArgv
	#include <dlfcn.h> // for dladdr()
	#include <mach-o/dyld.h>
	#include <mach-o/loader.h>
	#include <sys/mman.h>
	#include <sys/resource.h>
	#include <sys/sysctl.h>
	#include <sys/ucontext.h>
	#include <fcntl.h>
	#include <pthread.h>
	#include <stdlib.h> // for free()
	#include <unistd.h>
	#include <libkern/OSAtomic.h>

	namespace __asan {

	void InitializePlatformInterceptors() {}

	bool PlatformHasDifferentMemcpyAndMemmove() {
	// On OS X 10.7 memcpy() and memmove() are both resolved
	// into memmove$VARIANT$sse42.
	// See also http://code.google.com/p/address-sanitizer/issues/detail?id=34.
	// TODO(glider): need to check dynamically that memcpy() and memmove() are
	// actually the same function.
	return GetMacosVersion() == MACOS_VERSION_SNOW_LEOPARD;
	}

	extern "C"
	void __asan_init();

	static const char kDyldInsertLibraries[] = "DYLD_INSERT_LIBRARIES";
	LowLevelAllocator allocator_for_env;

	// Change the value of the env var \|name\|, leaking the original value.
	// If \|name_value\| is NULL, the variable is deleted from the environment,
	// otherwise the corresponding "NAME=value" string is replaced with
	// \|name_value\|.
	void LeakyResetEnv(const char name, const char name_value) {
	char ***env_ptr = _NSGetEnviron();
	CHECK(env_ptr);
	char *environ = env_ptr;
	CHECK(environ);
	uptr name_len = internal_strlen(name);
	while (*environ != 0) {
	uptr len = internal_strlen(*environ);
	if (len > name_len) {
	const char p = environ;
	if (!internal_memcmp(p, name, name_len) && p[name_len] == '=') {
	// Match.
	if (name_value) {
	// Replace the old value with the new one.
	environ = const_cast<char>(name_value);
	} else {
	// Shift the subsequent pointers back.
	char **del = environ;
	do {
	del[0] = del[1];
	} while (*del++);
	}
	}
	}
	environ++;
	}
	}

	static bool reexec_disabled = false;

	void DisableReexec() {
	reexec_disabled = true;
	}

	void MaybeReexec() {
	if (reexec_disabled) return;

	// Make sure the dynamic ASan runtime library is preloaded so that the
	// wrappers work. If it is not, set DYLD_INSERT_LIBRARIES and re-exec
	// ourselves.
	Dl_info info;
	CHECK(dladdr((void*)((uptr)__asan_init), &info));
	char *dyld_insert_libraries =
	const_cast<char*>(GetEnv(kDyldInsertLibraries));
	uptr old_env_len = dyld_insert_libraries ?
	internal_strlen(dyld_insert_libraries) : 0;
	uptr fname_len = internal_strlen(info.dli_fname);
	const char *dylib_name = StripModuleName(info.dli_fname);
	uptr dylib_name_len = internal_strlen(dylib_name);
	if (!dyld_insert_libraries \|\|
	!REAL(strstr)(dyld_insert_libraries, dylib_name)) {
	// DYLD_INSERT_LIBRARIES is not set or does not contain the runtime
	// library.
	char program_name[1024];
	uint32_t buf_size = sizeof(program_name);
	_NSGetExecutablePath(program_name, &buf_size);
	char new_env = const_cast<char>(info.dli_fname);
	if (dyld_insert_libraries) {
	// Append the runtime dylib name to the existing value of
	// DYLD_INSERT_LIBRARIES.
	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);
	// Ok to use setenv() since the wrappers don't depend on the value of
	// asan_inited.
	setenv(kDyldInsertLibraries, new_env, /overwrite/1);
	} else {
	// Set DYLD_INSERT_LIBRARIES equal to the runtime dylib name.
	setenv(kDyldInsertLibraries, info.dli_fname, /overwrite/0);
	}
	VReport(1, "exec()-ing the program with\n");
	VReport(1, "%s=%s\n", kDyldInsertLibraries, new_env);
	VReport(1, "to enable ASan wrappers.\n");
	execv(program_name, *_NSGetArgv());

	// We get here only if execv() failed.
	Report("ERROR: The process is launched without DYLD_INSERT_LIBRARIES, "
	"which is required for ASan to work. ASan tried to set the "
	"environment variable and re-execute itself, but execv() failed, "
	"possibly because of sandbox restrictions. Make sure to launch the "
	"executable with:\n%s=%s\n", kDyldInsertLibraries, new_env);
	CHECK("execv failed" && 0);
	}

	// DYLD_INSERT_LIBRARIES is set and contains the runtime library. Let's remove
	// the dylib from the environment variable, because interceptors are installed
	// and we don't want our children to inherit the variable.

	uptr env_name_len = internal_strlen(kDyldInsertLibraries);
	// Allocate memory to hold the previous env var name, its value, the '='
	// sign and the '\0' char.
	char new_env = (char)allocator_for_env.Allocate(
	old_env_len + 2 + env_name_len);
	CHECK(new_env);
	internal_memset(new_env, '\0', old_env_len + 2 + env_name_len);
	internal_strncpy(new_env, kDyldInsertLibraries, env_name_len);
	new_env[env_name_len] = '=';
	char *new_env_pos = new_env + env_name_len + 1;

	// Iterate over colon-separated pieces of \|dyld_insert_libraries\|.
	char *piece_start = dyld_insert_libraries;
	char *piece_end = NULL;
	char *old_env_end = dyld_insert_libraries + old_env_len;
	do {
	if (piece_start[0] == ':') piece_start++;
	piece_end = REAL(strchr)(piece_start, ':');
	if (!piece_end) piece_end = dyld_insert_libraries + old_env_len;
	if ((uptr)(piece_start - dyld_insert_libraries) > old_env_len) break;
	uptr piece_len = piece_end - piece_start;

	char *filename_start =
	(char *)internal_memrchr(piece_start, '/', piece_len);
	uptr filename_len = piece_len;
	if (filename_start) {
	filename_start += 1;
	filename_len = piece_len - (filename_start - piece_start);
	} else {
	filename_start = piece_start;
	}

	// If the current piece isn't the runtime library name,
	// append it to new_env.
	if ((dylib_name_len != filename_len) \|\|
	(internal_memcmp(filename_start, dylib_name, dylib_name_len) != 0)) {
	if (new_env_pos != new_env + env_name_len + 1) {
	new_env_pos[0] = ':';
	new_env_pos++;
	}
	internal_strncpy(new_env_pos, piece_start, piece_len);
	new_env_pos += piece_len;
	}
	// Move on to the next piece.
	piece_start = piece_end;
	} while (piece_start < old_env_end);

	// Can't use setenv() here, because it requires the allocator to be
	// initialized.
	// FIXME: instead of filtering DYLD_INSERT_LIBRARIES here, do it in
	// a separate function called after InitializeAllocator().
	if (new_env_pos == new_env + env_name_len + 1) new_env = NULL;
	LeakyResetEnv(kDyldInsertLibraries, new_env);
	}

	// No-op. Mac does not support static linkage anyway.
	void *AsanDoesNotSupportStaticLinkage() {
	return 0;
	}

	// No-op. Mac does not support static linkage anyway.
	void AsanCheckDynamicRTPrereqs() {}

	// No-op. Mac does not support static linkage anyway.
	void AsanCheckIncompatibleRT() {}

	void AsanPlatformThreadInit() {
	}

	void ReadContextStack(void context, uptr stack, uptr *ssize) {
	UNIMPLEMENTED();
	}

	// Support for the following functions from libdispatch on Mac OS:
	// dispatch_async_f()
	// dispatch_async()
	// dispatch_sync_f()
	// dispatch_sync()
	// dispatch_after_f()
	// dispatch_after()
	// dispatch_group_async_f()
	// dispatch_group_async()
	// TODO(glider): libdispatch API contains other functions that we don't support
	// yet.
	//
	// dispatch_sync() and dispatch_sync_f() are synchronous, although chances are
	// they can cause jobs to run on a thread different from the current one.
	// TODO(glider): if so, we need a test for this (otherwise we should remove
	// them).
	//
	// The following functions use dispatch_barrier_async_f() (which isn't a library
	// function but is exported) and are thus supported:
	// dispatch_source_set_cancel_handler_f()
	// dispatch_source_set_cancel_handler()
	// dispatch_source_set_event_handler_f()
	// dispatch_source_set_event_handler()
	//
	// The reference manual for Grand Central Dispatch is available at
	// http://developer.apple.com/library/mac/#documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html
	// The implementation details are at
	// http://libdispatch.macosforge.org/trac/browser/trunk/src/queue.c

	typedef void* dispatch_group_t;
	typedef void* dispatch_queue_t;
	typedef void* dispatch_source_t;
	typedef u64 dispatch_time_t;
	typedef void (dispatch_function_t)(void block);
	typedef void* (worker_t)(void block);

	// A wrapper for the ObjC blocks used to support libdispatch.
	typedef struct {
	void *block;
	dispatch_function_t func;
	u32 parent_tid;
	} asan_block_context_t;

	ALWAYS_INLINE
	void asan_register_worker_thread(int parent_tid, StackTrace *stack) {
	AsanThread *t = GetCurrentThread();
	if (!t) {
	t = AsanThread::Create(/* start_routine / nullptr, / arg */ nullptr,
	parent_tid, stack, /* detached */ true);
	t->Init();
	asanThreadRegistry().StartThread(t->tid(), 0, 0);
	SetCurrentThread(t);
	}
	}

	// For use by only those functions that allocated the context via
	// alloc_asan_context().
	extern "C"
	void asan_dispatch_call_block_and_release(void *block) {
	GET_STACK_TRACE_THREAD;
	asan_block_context_t context = (asan_block_context_t)block;
	VReport(2,
	"asan_dispatch_call_block_and_release(): "
	"context: %p, pthread_self: %p\n",
	block, pthread_self());
	asan_register_worker_thread(context->parent_tid, &stack);
	// Call the original dispatcher for the block.
	context->func(context->block);
	asan_free(context, &stack, FROM_MALLOC);
	}

	} // namespace __asan

	using namespace __asan; // NOLINT

	// Wrap \|ctxt\| and \|func\| into an asan_block_context_t.
	// The caller retains control of the allocated context.
	extern "C"
	asan_block_context_t alloc_asan_context(void ctxt, dispatch_function_t func,
	BufferedStackTrace *stack) {
	asan_block_context_t *asan_ctxt =
	(asan_block_context_t*) asan_malloc(sizeof(asan_block_context_t), stack);
	asan_ctxt->block = ctxt;
	asan_ctxt->func = func;
	asan_ctxt->parent_tid = GetCurrentTidOrInvalid();
	return asan_ctxt;
	}

	// Define interceptor for dispatch_*_f function with the three most common
	// parameters: dispatch_queue_t, context, dispatch_function_t.
	#define INTERCEPT_DISPATCH_X_F_3(dispatch_x_f) \
	INTERCEPTOR(void, dispatch_x_f, dispatch_queue_t dq, void *ctxt, \
	dispatch_function_t func) { \
	GET_STACK_TRACE_THREAD; \
	asan_block_context_t *asan_ctxt = alloc_asan_context(ctxt, func, &stack); \
	if (Verbosity() >= 2) { \
	Report(#dispatch_x_f "(): context: %p, pthread_self: %p\n", \
	asan_ctxt, pthread_self()); \
	PRINT_CURRENT_STACK(); \
	} \
	return REAL(dispatch_x_f)(dq, (void*)asan_ctxt, \
	asan_dispatch_call_block_and_release); \
	}

	INTERCEPT_DISPATCH_X_F_3(dispatch_async_f)
	INTERCEPT_DISPATCH_X_F_3(dispatch_sync_f)
	INTERCEPT_DISPATCH_X_F_3(dispatch_barrier_async_f)

	INTERCEPTOR(void, dispatch_after_f, dispatch_time_t when,
	dispatch_queue_t dq, void *ctxt,
	dispatch_function_t func) {
	GET_STACK_TRACE_THREAD;
	asan_block_context_t *asan_ctxt = alloc_asan_context(ctxt, func, &stack);
	if (Verbosity() >= 2) {
	Report("dispatch_after_f: %p\n", asan_ctxt);
	PRINT_CURRENT_STACK();
	}
	return REAL(dispatch_after_f)(when, dq, (void*)asan_ctxt,
	asan_dispatch_call_block_and_release);
	}

	INTERCEPTOR(void, dispatch_group_async_f, dispatch_group_t group,
	dispatch_queue_t dq, void *ctxt,
	dispatch_function_t func) {
	GET_STACK_TRACE_THREAD;
	asan_block_context_t *asan_ctxt = alloc_asan_context(ctxt, func, &stack);
	if (Verbosity() >= 2) {
	Report("dispatch_group_async_f(): context: %p, pthread_self: %p\n",
	asan_ctxt, pthread_self());
	PRINT_CURRENT_STACK();
	}
	REAL(dispatch_group_async_f)(group, dq, (void*)asan_ctxt,
	asan_dispatch_call_block_and_release);
	}

	#if !defined(MISSING_BLOCKS_SUPPORT)
	extern "C" {
	void dispatch_async(dispatch_queue_t dq, void(^work)(void));
	void dispatch_group_async(dispatch_group_t dg, dispatch_queue_t dq,
	void(^work)(void));
	void dispatch_after(dispatch_time_t when, dispatch_queue_t queue,
	void(^work)(void));
	void dispatch_source_set_cancel_handler(dispatch_source_t ds,
	void(^work)(void));
	void dispatch_source_set_event_handler(dispatch_source_t ds, void(^work)(void));
	}

	#define GET_ASAN_BLOCK(work) \
	void (^asan_block)(void); \
	int parent_tid = GetCurrentTidOrInvalid(); \
	asan_block = ^(void) { \
	GET_STACK_TRACE_THREAD; \
	asan_register_worker_thread(parent_tid, &stack); \
	work(); \
	}

	INTERCEPTOR(void, dispatch_async,
	dispatch_queue_t dq, void(^work)(void)) {
	ENABLE_FRAME_POINTER;
	GET_ASAN_BLOCK(work);
	REAL(dispatch_async)(dq, asan_block);
	}

	INTERCEPTOR(void, dispatch_group_async,
	dispatch_group_t dg, dispatch_queue_t dq, void(^work)(void)) {
	ENABLE_FRAME_POINTER;
	GET_ASAN_BLOCK(work);
	REAL(dispatch_group_async)(dg, dq, asan_block);
	}

	INTERCEPTOR(void, dispatch_after,
	dispatch_time_t when, dispatch_queue_t queue, void(^work)(void)) {
	ENABLE_FRAME_POINTER;
	GET_ASAN_BLOCK(work);
	REAL(dispatch_after)(when, queue, asan_block);
	}

	INTERCEPTOR(void, dispatch_source_set_cancel_handler,
	dispatch_source_t ds, void(^work)(void)) {
	if (!work) {
	REAL(dispatch_source_set_cancel_handler)(ds, work);
	return;
	}
	ENABLE_FRAME_POINTER;
	GET_ASAN_BLOCK(work);
	REAL(dispatch_source_set_cancel_handler)(ds, asan_block);
	}

	INTERCEPTOR(void, dispatch_source_set_event_handler,
	dispatch_source_t ds, void(^work)(void)) {
	ENABLE_FRAME_POINTER;
	GET_ASAN_BLOCK(work);
	REAL(dispatch_source_set_event_handler)(ds, asan_block);
	}
	#endif

	#endif // SANITIZER_MAC