src/base/platform/platform-linux.cc - platform/external/v8 - Git at Google

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 // Platform-specific code for Linux goes here. For the POSIX-compatible
 // parts, the implementation is in platform-posix.cc.

 #include <pthread.h>
 #include <semaphore.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/resource.h>
 #include <sys/time.h>

 // Ubuntu Dapper requires memory pages to be marked as
 // executable. Otherwise, OS raises an exception when executing code
 // in that page.
 #include <errno.h>
 #include <fcntl.h>      // open
 #include <stdarg.h>
 #include <strings.h>    // index
 #include <sys/mman.h>   // mmap & munmap
 #include <sys/stat.h>   // open
 #include <sys/types.h>  // mmap & munmap
 #include <unistd.h>     // sysconf

 // GLibc on ARM defines mcontext_t has a typedef for 'struct sigcontext'.
 // Old versions of the C library <signal.h> didn't define the type.
 #if defined(__ANDROID__) && !defined(__BIONIC_HAVE_UCONTEXT_T) && \
     (defined(__arm__) || defined(__aarch64__)) && \
     !defined(__BIONIC_HAVE_STRUCT_SIGCONTEXT)
 #include <asm/sigcontext.h>  // NOLINT
 #endif

 #if defined(LEAK_SANITIZER)
 #include <sanitizer/lsan_interface.h>
 #endif

 #include <cmath>

 #undef MAP_TYPE

 #include "src/base/macros.h"
 #include "src/base/platform/platform.h"

 #if V8_OS_NACL
 #if !defined(MAP_NORESERVE)
 // PNaCL doesn't have this, so we always grab all of the memory, which is bad.
 #define MAP_NORESERVE 0
 #endif
 #else
 #include <sys/prctl.h>
 #include <sys/syscall.h>
 #endif

 namespace v8 {
 namespace base {


 #ifdef __arm__

 bool OS::ArmUsingHardFloat() {
   // GCC versions 4.6 and above define __ARM_PCS or __ARM_PCS_VFP to specify
   // the Floating Point ABI used (PCS stands for Procedure Call Standard).
   // We use these as well as a couple of other defines to statically determine
   // what FP ABI used.
   // GCC versions 4.4 and below don't support hard-fp.
   // GCC versions 4.5 may support hard-fp without defining __ARM_PCS or
   // __ARM_PCS_VFP.

 #define GCC_VERSION (__GNUC__ * 10000                                          \
                      + __GNUC_MINOR__ * 100                                    \
                      + __GNUC_PATCHLEVEL__)
 #if GCC_VERSION >= 40600
 #if defined(__ARM_PCS_VFP)
   return true;
 #else
   return false;
 #endif

 #elif GCC_VERSION < 40500
   return false;

 #else
 #if defined(__ARM_PCS_VFP)
   return true;
 #elif defined(__ARM_PCS) || defined(__SOFTFP__) || defined(__SOFTFP) || \
       !defined(__VFP_FP__)
   return false;
 #else
 #error "Your version of GCC does not report the FP ABI compiled for."          \
        "Please report it on this issue"                                        \
        "http://code.google.com/p/v8/issues/detail?id=2140"

 #endif
 #endif
 #undef GCC_VERSION
 }

 #endif  // def __arm__


 const char* OS::LocalTimezone(double time, TimezoneCache* cache) {
 #if V8_OS_NACL
   // Missing support for tm_zone field.
   return "";
 #else
   if (std::isnan(time)) return "";
   time_t tv = static_cast<time_t>(std::floor(time/msPerSecond));
   struct tm* t = localtime(&tv);  // NOLINT(runtime/threadsafe_fn)
   if (!t || !t->tm_zone) return "";
   return t->tm_zone;
 #endif
 }


 double OS::LocalTimeOffset(TimezoneCache* cache) {
 #if V8_OS_NACL
   // Missing support for tm_zone field.
   return 0;
 #else
   time_t tv = time(NULL);
   struct tm* t = localtime(&tv);  // NOLINT(runtime/threadsafe_fn)
   // tm_gmtoff includes any daylight savings offset, so subtract it.
   return static_cast<double>(t->tm_gmtoff * msPerSecond -
                              (t->tm_isdst > 0 ? 3600 * msPerSecond : 0));
 #endif
 }


 void* OS::Allocate(const size_t requested,
                    size_t* allocated,
                    bool is_executable) {
   const size_t msize = RoundUp(requested, AllocateAlignment());
   int prot = PROT_READ | PROT_WRITE | (is_executable ? PROT_EXEC : 0);
   void* addr = OS::GetRandomMmapAddr();
   void* mbase = mmap(addr, msize, prot, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
   if (mbase == MAP_FAILED) return NULL;
   *allocated = msize;
   return mbase;
 }


 std::vector<OS::SharedLibraryAddress> OS::GetSharedLibraryAddresses() {
   std::vector<SharedLibraryAddress> result;
   // This function assumes that the layout of the file is as follows:
   // hex_start_addr-hex_end_addr rwxp <unused data> [binary_file_name]
   // If we encounter an unexpected situation we abort scanning further entries.
   FILE* fp = fopen("/proc/self/maps", "r");
   if (fp == NULL) return result;

   // Allocate enough room to be able to store a full file name.
   const int kLibNameLen = FILENAME_MAX + 1;
   char* lib_name = reinterpret_cast<char*>(malloc(kLibNameLen));

   // This loop will terminate once the scanning hits an EOF.
   while (true) {
     uintptr_t start, end;
     char attr_r, attr_w, attr_x, attr_p;
     // Parse the addresses and permission bits at the beginning of the line.
     if (fscanf(fp, "%" V8PRIxPTR "-%" V8PRIxPTR, &start, &end) != 2) break;
     if (fscanf(fp, " %c%c%c%c", &attr_r, &attr_w, &attr_x, &attr_p) != 4) break;

     int c;
     if (attr_r == 'r' && attr_w != 'w' && attr_x == 'x') {
       // Found a read-only executable entry. Skip characters until we reach
       // the beginning of the filename or the end of the line.
       do {
         c = getc(fp);
       } while ((c != EOF) && (c != '\n') && (c != '/') && (c != '['));
       if (c == EOF) break;  // EOF: Was unexpected, just exit.

       // Process the filename if found.
       if ((c == '/') || (c == '[')) {
         // Push the '/' or '[' back into the stream to be read below.
         ungetc(c, fp);

         // Read to the end of the line. Exit if the read fails.
         if (fgets(lib_name, kLibNameLen, fp) == NULL) break;

         // Drop the newline character read by fgets. We do not need to check
         // for a zero-length string because we know that we at least read the
         // '/' or '[' character.
         lib_name[strlen(lib_name) - 1] = '\0';
       } else {
         // No library name found, just record the raw address range.
         snprintf(lib_name, kLibNameLen,
                  "%08" V8PRIxPTR "-%08" V8PRIxPTR, start, end);
       }
       result.push_back(SharedLibraryAddress(lib_name, start, end));
     } else {
       // Entry not describing executable data. Skip to end of line to set up
       // reading the next entry.
       do {
         c = getc(fp);
       } while ((c != EOF) && (c != '\n'));
       if (c == EOF) break;
     }
   }
   free(lib_name);
   fclose(fp);
   return result;
 }


 void OS::SignalCodeMovingGC() {
   // Support for ll_prof.py.
   //
   // The Linux profiler built into the kernel logs all mmap's with
   // PROT_EXEC so that analysis tools can properly attribute ticks. We
   // do a mmap with a name known by ll_prof.py and immediately munmap
   // it. This injects a GC marker into the stream of events generated
   // by the kernel and allows us to synchronize V8 code log and the
   // kernel log.
   long size = sysconf(_SC_PAGESIZE);  // NOLINT(runtime/int)
   FILE* f = fopen(OS::GetGCFakeMMapFile(), "w+");
   if (f == NULL) {
     OS::PrintError("Failed to open %s\n", OS::GetGCFakeMMapFile());
     OS::Abort();
   }
   void* addr = mmap(OS::GetRandomMmapAddr(), size,
 #if V8_OS_NACL
                     // The Native Client port of V8 uses an interpreter,
                     // so code pages don't need PROT_EXEC.
                     PROT_READ,
 #else
                     PROT_READ | PROT_EXEC,
 #endif
                     MAP_PRIVATE, fileno(f), 0);
   DCHECK_NE(MAP_FAILED, addr);
   OS::Free(addr, size);
   fclose(f);
 }


 // Constants used for mmap.
 static const int kMmapFd = -1;
 static const int kMmapFdOffset = 0;


 VirtualMemory::VirtualMemory() : address_(NULL), size_(0) { }


 VirtualMemory::VirtualMemory(size_t size)
     : address_(ReserveRegion(size)), size_(size) { }


 VirtualMemory::VirtualMemory(size_t size, size_t alignment)
     : address_(NULL), size_(0) {
   DCHECK((alignment % OS::AllocateAlignment()) == 0);
   size_t request_size = RoundUp(size + alignment,
                                 static_cast<intptr_t>(OS::AllocateAlignment()));
   void* reservation = mmap(OS::GetRandomMmapAddr(),
                            request_size,
                            PROT_NONE,
                            MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE,
                            kMmapFd,
                            kMmapFdOffset);
   if (reservation == MAP_FAILED) return;

   uint8_t* base = static_cast<uint8_t*>(reservation);
   uint8_t* aligned_base = RoundUp(base, alignment);
   DCHECK_LE(base, aligned_base);

   // Unmap extra memory reserved before and after the desired block.
   if (aligned_base != base) {
     size_t prefix_size = static_cast<size_t>(aligned_base - base);
     OS::Free(base, prefix_size);
     request_size -= prefix_size;
   }

   size_t aligned_size = RoundUp(size, OS::AllocateAlignment());
   DCHECK_LE(aligned_size, request_size);

   if (aligned_size != request_size) {
     size_t suffix_size = request_size - aligned_size;
     OS::Free(aligned_base + aligned_size, suffix_size);
     request_size -= suffix_size;
   }

   DCHECK(aligned_size == request_size);

   address_ = static_cast<void*>(aligned_base);
   size_ = aligned_size;
 #if defined(LEAK_SANITIZER)
   __lsan_register_root_region(address_, size_);
 #endif
 }


 VirtualMemory::~VirtualMemory() {
   if (IsReserved()) {
     bool result = ReleaseRegion(address(), size());
     DCHECK(result);
     USE(result);
   }
 }


 bool VirtualMemory::IsReserved() {
   return address_ != NULL;
 }


 void VirtualMemory::Reset() {
   address_ = NULL;
   size_ = 0;
 }


 bool VirtualMemory::Commit(void* address, size_t size, bool is_executable) {
   CHECK(InVM(address, size));
   return CommitRegion(address, size, is_executable);
 }


 bool VirtualMemory::Uncommit(void* address, size_t size) {
   CHECK(InVM(address, size));
   return UncommitRegion(address, size);
 }


 bool VirtualMemory::Guard(void* address) {
   CHECK(InVM(address, OS::CommitPageSize()));
   OS::Guard(address, OS::CommitPageSize());
   return true;
 }


 void* VirtualMemory::ReserveRegion(size_t size) {
   void* result = mmap(OS::GetRandomMmapAddr(),
                       size,
                       PROT_NONE,
                       MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE,
                       kMmapFd,
                       kMmapFdOffset);

   if (result == MAP_FAILED) return NULL;

 #if defined(LEAK_SANITIZER)
   __lsan_register_root_region(result, size);
 #endif
   return result;
 }


 bool VirtualMemory::CommitRegion(void* base, size_t size, bool is_executable) {
 #if V8_OS_NACL
   // The Native Client port of V8 uses an interpreter,
   // so code pages don't need PROT_EXEC.
   int prot = PROT_READ | PROT_WRITE;
 #else
   int prot = PROT_READ | PROT_WRITE | (is_executable ? PROT_EXEC : 0);
 #endif
   if (MAP_FAILED == mmap(base,
                          size,
                          prot,
                          MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED,
                          kMmapFd,
                          kMmapFdOffset)) {
     return false;
   }

   return true;
 }


 bool VirtualMemory::UncommitRegion(void* base, size_t size) {
   return mmap(base,
               size,
               PROT_NONE,
               MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE | MAP_FIXED,
               kMmapFd,
               kMmapFdOffset) != MAP_FAILED;
 }


 bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
 #if defined(LEAK_SANITIZER)
   __lsan_unregister_root_region(base, size);
 #endif
   return munmap(base, size) == 0;
 }


 bool VirtualMemory::HasLazyCommits() {
   return true;
 }

 }  // namespace base
 }  // namespace v8
	// Copyright 2012 the V8 project authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	// Platform-specific code for Linux goes here. For the POSIX-compatible
	// parts, the implementation is in platform-posix.cc.

	#include <pthread.h>
	#include <semaphore.h>
	#include <signal.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <sys/resource.h>
	#include <sys/time.h>

	// Ubuntu Dapper requires memory pages to be marked as
	// executable. Otherwise, OS raises an exception when executing code
	// in that page.
	#include <errno.h>
	#include <fcntl.h> // open
	#include <stdarg.h>
	#include <strings.h> // index
	#include <sys/mman.h> // mmap & munmap
	#include <sys/stat.h> // open
	#include <sys/types.h> // mmap & munmap
	#include <unistd.h> // sysconf

	// GLibc on ARM defines mcontext_t has a typedef for 'struct sigcontext'.
	// Old versions of the C library <signal.h> didn't define the type.
	#if defined(__ANDROID__) && !defined(__BIONIC_HAVE_UCONTEXT_T) && \
	(defined(__arm__) \|\| defined(__aarch64__)) && \
	!defined(__BIONIC_HAVE_STRUCT_SIGCONTEXT)
	#include <asm/sigcontext.h> // NOLINT
	#endif

	#if defined(LEAK_SANITIZER)
	#include <sanitizer/lsan_interface.h>
	#endif

	#include <cmath>

	#undef MAP_TYPE

	#include "src/base/macros.h"
	#include "src/base/platform/platform.h"

	#if V8_OS_NACL
	#if !defined(MAP_NORESERVE)
	// PNaCL doesn't have this, so we always grab all of the memory, which is bad.
	#define MAP_NORESERVE 0
	#endif
	#else
	#include <sys/prctl.h>
	#include <sys/syscall.h>
	#endif

	namespace v8 {
	namespace base {


	#ifdef __arm__

	bool OS::ArmUsingHardFloat() {
	// GCC versions 4.6 and above define __ARM_PCS or __ARM_PCS_VFP to specify
	// the Floating Point ABI used (PCS stands for Procedure Call Standard).
	// We use these as well as a couple of other defines to statically determine
	// what FP ABI used.
	// GCC versions 4.4 and below don't support hard-fp.
	// GCC versions 4.5 may support hard-fp without defining __ARM_PCS or
	// __ARM_PCS_VFP.

	#define GCC_VERSION (__GNUC__ * 10000 \
	+ __GNUC_MINOR__ * 100 \
	+ __GNUC_PATCHLEVEL__)
	#if GCC_VERSION >= 40600
	#if defined(__ARM_PCS_VFP)
	return true;
	#else
	return false;
	#endif

	#elif GCC_VERSION < 40500
	return false;

	#else
	#if defined(__ARM_PCS_VFP)
	return true;
	#elif defined(__ARM_PCS) \|\| defined(__SOFTFP__) \|\| defined(__SOFTFP) \|\| \
	!defined(__VFP_FP__)
	return false;
	#else
	#error "Your version of GCC does not report the FP ABI compiled for." \
	"Please report it on this issue" \
	"http://code.google.com/p/v8/issues/detail?id=2140"

	#endif
	#endif
	#undef GCC_VERSION
	}

	#endif // def __arm__


	const char* OS::LocalTimezone(double time, TimezoneCache* cache) {
	#if V8_OS_NACL
	// Missing support for tm_zone field.
	return "";
	#else
	if (std::isnan(time)) return "";
	time_t tv = static_cast<time_t>(std::floor(time/msPerSecond));
	struct tm* t = localtime(&tv); // NOLINT(runtime/threadsafe_fn)
	if (!t \|\| !t->tm_zone) return "";
	return t->tm_zone;
	#endif
	}


	double OS::LocalTimeOffset(TimezoneCache* cache) {
	#if V8_OS_NACL
	// Missing support for tm_zone field.
	return 0;
	#else
	time_t tv = time(NULL);
	struct tm* t = localtime(&tv); // NOLINT(runtime/threadsafe_fn)
	// tm_gmtoff includes any daylight savings offset, so subtract it.
	return static_cast<double>(t->tm_gmtoff * msPerSecond -
	(t->tm_isdst > 0 ? 3600 * msPerSecond : 0));
	#endif
	}


	void* OS::Allocate(const size_t requested,
	size_t* allocated,
	bool is_executable) {
	const size_t msize = RoundUp(requested, AllocateAlignment());
	int prot = PROT_READ \| PROT_WRITE \| (is_executable ? PROT_EXEC : 0);
	void* addr = OS::GetRandomMmapAddr();
	void* mbase = mmap(addr, msize, prot, MAP_PRIVATE \| MAP_ANONYMOUS, -1, 0);
	if (mbase == MAP_FAILED) return NULL;
	*allocated = msize;
	return mbase;
	}


	std::vector<OS::SharedLibraryAddress> OS::GetSharedLibraryAddresses() {
	std::vector<SharedLibraryAddress> result;
	// This function assumes that the layout of the file is as follows:
	// hex_start_addr-hex_end_addr rwxp <unused data> [binary_file_name]
	// If we encounter an unexpected situation we abort scanning further entries.
	FILE* fp = fopen("/proc/self/maps", "r");
	if (fp == NULL) return result;

	// Allocate enough room to be able to store a full file name.
	const int kLibNameLen = FILENAME_MAX + 1;
	char* lib_name = reinterpret_cast<char*>(malloc(kLibNameLen));

	// This loop will terminate once the scanning hits an EOF.
	while (true) {
	uintptr_t start, end;
	char attr_r, attr_w, attr_x, attr_p;
	// Parse the addresses and permission bits at the beginning of the line.
	if (fscanf(fp, "%" V8PRIxPTR "-%" V8PRIxPTR, &start, &end) != 2) break;
	if (fscanf(fp, " %c%c%c%c", &attr_r, &attr_w, &attr_x, &attr_p) != 4) break;

	int c;
	if (attr_r == 'r' && attr_w != 'w' && attr_x == 'x') {
	// Found a read-only executable entry. Skip characters until we reach
	// the beginning of the filename or the end of the line.
	do {
	c = getc(fp);
	} while ((c != EOF) && (c != '\n') && (c != '/') && (c != '['));
	if (c == EOF) break; // EOF: Was unexpected, just exit.

	// Process the filename if found.
	if ((c == '/') \|\| (c == '[')) {
	// Push the '/' or '[' back into the stream to be read below.
	ungetc(c, fp);

	// Read to the end of the line. Exit if the read fails.
	if (fgets(lib_name, kLibNameLen, fp) == NULL) break;

	// Drop the newline character read by fgets. We do not need to check
	// for a zero-length string because we know that we at least read the
	// '/' or '[' character.
	lib_name[strlen(lib_name) - 1] = '\0';
	} else {
	// No library name found, just record the raw address range.
	snprintf(lib_name, kLibNameLen,
	"%08" V8PRIxPTR "-%08" V8PRIxPTR, start, end);
	}
	result.push_back(SharedLibraryAddress(lib_name, start, end));
	} else {
	// Entry not describing executable data. Skip to end of line to set up
	// reading the next entry.
	do {
	c = getc(fp);
	} while ((c != EOF) && (c != '\n'));
	if (c == EOF) break;
	}
	}
	free(lib_name);
	fclose(fp);
	return result;
	}


	void OS::SignalCodeMovingGC() {
	// Support for ll_prof.py.
	//
	// The Linux profiler built into the kernel logs all mmap's with
	// PROT_EXEC so that analysis tools can properly attribute ticks. We
	// do a mmap with a name known by ll_prof.py and immediately munmap
	// it. This injects a GC marker into the stream of events generated
	// by the kernel and allows us to synchronize V8 code log and the
	// kernel log.
	long size = sysconf(_SC_PAGESIZE); // NOLINT(runtime/int)
	FILE* f = fopen(OS::GetGCFakeMMapFile(), "w+");
	if (f == NULL) {
	OS::PrintError("Failed to open %s\n", OS::GetGCFakeMMapFile());
	OS::Abort();
	}
	void* addr = mmap(OS::GetRandomMmapAddr(), size,
	#if V8_OS_NACL
	// The Native Client port of V8 uses an interpreter,
	// so code pages don't need PROT_EXEC.
	PROT_READ,
	#else
	PROT_READ \| PROT_EXEC,
	#endif
	MAP_PRIVATE, fileno(f), 0);
	DCHECK_NE(MAP_FAILED, addr);
	OS::Free(addr, size);
	fclose(f);
	}


	// Constants used for mmap.
	static const int kMmapFd = -1;
	static const int kMmapFdOffset = 0;


	VirtualMemory::VirtualMemory() : address_(NULL), size_(0) { }


	VirtualMemory::VirtualMemory(size_t size)
	: address_(ReserveRegion(size)), size_(size) { }


	VirtualMemory::VirtualMemory(size_t size, size_t alignment)
	: address_(NULL), size_(0) {
	DCHECK((alignment % OS::AllocateAlignment()) == 0);
	size_t request_size = RoundUp(size + alignment,
	static_cast<intptr_t>(OS::AllocateAlignment()));
	void* reservation = mmap(OS::GetRandomMmapAddr(),
	request_size,
	PROT_NONE,
	MAP_PRIVATE \| MAP_ANONYMOUS \| MAP_NORESERVE,
	kMmapFd,
	kMmapFdOffset);
	if (reservation == MAP_FAILED) return;

	uint8_t* base = static_cast<uint8_t*>(reservation);
	uint8_t* aligned_base = RoundUp(base, alignment);
	DCHECK_LE(base, aligned_base);

	// Unmap extra memory reserved before and after the desired block.
	if (aligned_base != base) {
	size_t prefix_size = static_cast<size_t>(aligned_base - base);
	OS::Free(base, prefix_size);
	request_size -= prefix_size;
	}

	size_t aligned_size = RoundUp(size, OS::AllocateAlignment());
	DCHECK_LE(aligned_size, request_size);

	if (aligned_size != request_size) {
	size_t suffix_size = request_size - aligned_size;
	OS::Free(aligned_base + aligned_size, suffix_size);
	request_size -= suffix_size;
	}

	DCHECK(aligned_size == request_size);

	address_ = static_cast<void*>(aligned_base);
	size_ = aligned_size;
	#if defined(LEAK_SANITIZER)
	__lsan_register_root_region(address_, size_);
	#endif
	}


	VirtualMemory::~VirtualMemory() {
	if (IsReserved()) {
	bool result = ReleaseRegion(address(), size());
	DCHECK(result);
	USE(result);
	}
	}


	bool VirtualMemory::IsReserved() {
	return address_ != NULL;
	}


	void VirtualMemory::Reset() {
	address_ = NULL;
	size_ = 0;
	}


	bool VirtualMemory::Commit(void* address, size_t size, bool is_executable) {
	CHECK(InVM(address, size));
	return CommitRegion(address, size, is_executable);
	}


	bool VirtualMemory::Uncommit(void* address, size_t size) {
	CHECK(InVM(address, size));
	return UncommitRegion(address, size);
	}


	bool VirtualMemory::Guard(void* address) {
	CHECK(InVM(address, OS::CommitPageSize()));
	OS::Guard(address, OS::CommitPageSize());
	return true;
	}


	void* VirtualMemory::ReserveRegion(size_t size) {
	void* result = mmap(OS::GetRandomMmapAddr(),
	size,
	PROT_NONE,
	MAP_PRIVATE \| MAP_ANONYMOUS \| MAP_NORESERVE,
	kMmapFd,
	kMmapFdOffset);

	if (result == MAP_FAILED) return NULL;

	#if defined(LEAK_SANITIZER)
	__lsan_register_root_region(result, size);
	#endif
	return result;
	}


	bool VirtualMemory::CommitRegion(void* base, size_t size, bool is_executable) {
	#if V8_OS_NACL
	// The Native Client port of V8 uses an interpreter,
	// so code pages don't need PROT_EXEC.
	int prot = PROT_READ \| PROT_WRITE;
	#else
	int prot = PROT_READ \| PROT_WRITE \| (is_executable ? PROT_EXEC : 0);
	#endif
	if (MAP_FAILED == mmap(base,
	size,
	prot,
	MAP_PRIVATE \| MAP_ANONYMOUS \| MAP_FIXED,
	kMmapFd,
	kMmapFdOffset)) {
	return false;
	}

	return true;
	}


	bool VirtualMemory::UncommitRegion(void* base, size_t size) {
	return mmap(base,
	size,
	PROT_NONE,
	MAP_PRIVATE \| MAP_ANONYMOUS \| MAP_NORESERVE \| MAP_FIXED,
	kMmapFd,
	kMmapFdOffset) != MAP_FAILED;
	}


	bool VirtualMemory::ReleaseRegion(void* base, size_t size) {
	#if defined(LEAK_SANITIZER)
	__lsan_unregister_root_region(base, size);
	#endif
	return munmap(base, size) == 0;
	}


	bool VirtualMemory::HasLazyCommits() {
	return true;
	}

	} // namespace base
	} // namespace v8