TaggedAnonymousMemory.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifdef XP_LINUX

#  include "mozilla/TaggedAnonymousMemory.h"

#  include <sys/types.h>
#  include <sys/mman.h>
#  include <sys/prctl.h>
#  include <sys/syscall.h>
#  include <unistd.h>

#  include "mozilla/Assertions.h"

// These constants are copied from <sys/prctl.h>, because the headers
// used for building may not have them even though the running kernel
// supports them.
#  ifndef PR_SET_VMA
#    define PR_SET_VMA 0x53564d41
#  endif
#  ifndef PR_SET_VMA_ANON_NAME
#    define PR_SET_VMA_ANON_NAME 0
#  endif

namespace mozilla {

// Returns 0 for success and -1 (with errno) for error.
static int TagAnonymousMemoryAligned(const void* aPtr, size_t aLength,
                                     const char* aTag) {
  return prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME,
               reinterpret_cast<unsigned long>(aPtr), aLength,
               reinterpret_cast<unsigned long>(aTag));
}

// On some architectures, it's possible for the page size to be larger
// than the PAGE_SIZE we were compiled with.  This computes the
// equivalent of PAGE_MASK.
static uintptr_t GetPageMask() {
  static uintptr_t mask = 0;

  if (mask == 0) {
    uintptr_t pageSize = sysconf(_SC_PAGESIZE);
    mask = ~(pageSize - 1);
    MOZ_ASSERT((pageSize & (pageSize - 1)) == 0,
               "Page size must be a power of 2!");
  }
  return mask;
}

}  // namespace mozilla

void MozTagAnonymousMemory(const void* aPtr, size_t aLength, const char* aTag) {
  // The kernel will round up the end of the range to the next page
  // boundary if it's not aligned (comments indicate this behavior is
  // based on that of madvise), but it will reject the request if the
  // start is not aligned.  We therefore round down the start address
  // and adjust the length accordingly.
  uintptr_t addr = reinterpret_cast<uintptr_t>(aPtr);
  uintptr_t end = addr + aLength;
  uintptr_t addrRounded = addr & mozilla::GetPageMask();
  const void* ptrRounded = reinterpret_cast<const void*>(addrRounded);

  // Ignore the return value. TagAnonymousMemoryAligned will harmlessly fail on
  // kernels without CONFIG_ANON_VMA_NAME.
  mozilla::TagAnonymousMemoryAligned(ptrRounded, end - addrRounded, aTag);
}

void* MozTaggedAnonymousMmap(void* aAddr, size_t aLength, int aProt, int aFlags,
                             int aFd, off_t aOffset, const char* aTag) {
  void* mapped = mmap(aAddr, aLength, aProt, aFlags, aFd, aOffset);
  if ((aFlags & MAP_ANONYMOUS) == MAP_ANONYMOUS && mapped != MAP_FAILED) {
    // Ignore the return value. TagAnonymousMemoryAligned will harmlessly fail
    // on kernels without CONFIG_ANON_VMA_NAME.
    mozilla::TagAnonymousMemoryAligned(mapped, aLength, aTag);
  }
  return mapped;
}

#endif  // XP_LINUX