src/base/platform/platform-linux.cc

// 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 && !defined(__clang__)
#if defined(__ARM_PCS_VFP)
  return true;
#else
  return false;
#endif

#elif GCC_VERSION < 40500 && !defined(__clang__)
  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 compiler 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