mfbt/TaggedAnonymousMemory.cpp

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifdef ANDROID
   8
   9 #include "mozilla/TaggedAnonymousMemory.h"
  10
  11 #include <sys/types.h>
  12 #include <sys/mman.h>
  13 #include <sys/prctl.h>
  14 #include <sys/syscall.h>
  15 #include <unistd.h>
  16
  17 #include "mozilla/Assertions.h"
  18 #include "mozilla/NullPtr.h"
  19
  20 // These constants are copied from <sys/prctl.h>, because the headers
  21 // used for building may not have them even though the running kernel
  22 // supports them.
  23 #ifndef PR_SET_VMA
  24 #define PR_SET_VMA              0x53564d41
  25 #endif
  26 #ifndef PR_SET_VMA_ANON_NAME
  27 #define PR_SET_VMA_ANON_NAME            0
  28 #endif
  29
  30 namespace mozilla {
  31
  32 // Returns 0 for success and -1 (with errno) for error.
  33 static int
  34 TagAnonymousMemoryAligned(const void* aPtr, size_t aLength, const char* aTag)
  35 {
  36   return prctl(PR_SET_VMA,
  37                PR_SET_VMA_ANON_NAME,
  38                reinterpret_cast<unsigned long>(aPtr),
  39                aLength,
  40                reinterpret_cast<unsigned long>(aTag));
  41 }
  42
  43 // On some architectures, it's possible for the page size to be larger
  44 // than the PAGE_SIZE we were compiled with.  This computes the
  45 // equivalent of PAGE_MASK.
  46 static uintptr_t
  47 GetPageMask()
  48 {
  49   static uintptr_t mask = 0;
  50
  51   if (mask == 0) {
  52     uintptr_t pageSize = sysconf(_SC_PAGESIZE);
  53     mask = ~(pageSize - 1);
  54     MOZ_ASSERT((pageSize & (pageSize - 1)) == 0,
  55                "Page size must be a power of 2!");
  56   }
  57   return mask;
  58 }
  59
  60 } // namespace mozilla
  61
  62 int
  63 MozTaggedMemoryIsSupported(void)
  64 {
  65   static int supported = -1;
  66
  67   if (supported == -1) {
  68     // Tagging an empty range always "succeeds" if the feature is supported,
  69     // regardless of the start pointer.
  70     supported = mozilla::TagAnonymousMemoryAligned(nullptr, 0, nullptr) == 0;
  71   }
  72   return supported;
  73 }
  74
  75 void
  76 MozTagAnonymousMemory(const void* aPtr, size_t aLength, const char* aTag)
  77 {
  78   if (MozTaggedMemoryIsSupported()) {
  79     // The kernel will round up the end of the range to the next page
  80     // boundary if it's not aligned (comments indicate this behavior
  81     // is based on that of madvise), but it will reject the request if
  82     // the start is not aligned.  We therefore round down the start
  83     // address and adjust the length accordingly.
  84     uintptr_t addr = reinterpret_cast<uintptr_t>(aPtr);
  85     uintptr_t end = addr + aLength;
  86     uintptr_t addrRounded = addr & mozilla::GetPageMask();
  87     const void* ptrRounded = reinterpret_cast<const void*>(addrRounded);
  88
  89     mozilla::TagAnonymousMemoryAligned(ptrRounded, end - addrRounded, aTag);
  90   }
  91 }
  92
  93 void*
  94 MozTaggedAnonymousMmap(void* aAddr, size_t aLength, int aProt, int aFlags,
  95                        int aFd, off_t aOffset, const char* aTag)
  96 {
  97   void* mapped = mmap(aAddr, aLength, aProt, aFlags, aFd, aOffset);
  98   if (MozTaggedMemoryIsSupported() &&
  99       (aFlags & MAP_ANONYMOUS) == MAP_ANONYMOUS &&
 100       mapped != MAP_FAILED) {
 101     mozilla::TagAnonymousMemoryAligned(mapped, aLength, aTag);
 102   }
 103   return mapped;
 104 }
 105
 106 #endif // ANDROID