wtf/OSAllocatorPosix.cpp

   1 /*
   2  * Copyright (C) 2010 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
  14  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  15  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
  17  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  18  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  19  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  20  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  21  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  22  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  23  * THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "config.h"
  27 #include "OSAllocator.h"
  28
  29 #include "PageAllocation.h"
  30 #include <errno.h>
  31 #include <sys/mman.h>
  32 #include <wtf/Assertions.h>
  33 #include <wtf/UnusedParam.h>
  34
  35 namespace WTF {
  36
  37 void* OSAllocator::reserveUncommitted(size_t bytes, Usage usage, bool writable, bool executable, bool includesGuardPages)
  38 {
  39     void* result = reserveAndCommit(bytes, usage, writable, executable, includesGuardPages);
  40 #if HAVE(MADV_FREE_REUSE)
  41     // To support the "reserve then commit" model, we have to initially decommit.
  42     while (madvise(result, bytes, MADV_FREE_REUSABLE) == -1 && errno == EAGAIN) { }
  43 #endif
  44     return result;
  45 }
  46
  47 void* OSAllocator::reserveAndCommit(size_t bytes, Usage usage, bool writable, bool executable, bool includesGuardPages)
  48 {
  49     // All POSIX reservations start out logically committed.
  50     int protection = PROT_READ;
  51     if (writable)
  52         protection |= PROT_WRITE;
  53     if (executable)
  54         protection |= PROT_EXEC;
  55
  56     int flags = MAP_PRIVATE | MAP_ANON;
  57 #if defined MAP_JIT
  58     if (executable)
  59         flags |= MAP_JIT;
  60 #endif
  61
  62 #if OS(DARWIN)
  63     int fd = usage;
  64 #else
  65     int fd = -1;
  66 #endif
  67
  68     void* result = 0;
  69 #if (OS(DARWIN) && CPU(X86_64))
  70     if (executable) {
  71         ASSERT(includesGuardPages);
  72         // Cook up an address to allocate at, using the following recipe:
  73         //   17 bits of zero, stay in userspace kids.
  74         //   26 bits of randomness for ASLR.
  75         //   21 bits of zero, at least stay aligned within one level of the pagetables.
  76         //
  77         // But! - as a temporary workaround for some plugin problems (rdar://problem/6812854),
  78         // for now instead of 2^26 bits of ASLR lets stick with 25 bits of randomization plus
  79         // 2^24, which should put up somewhere in the middle of userspace (in the address range
  80         // 0x200000000000 .. 0x5fffffffffff).
  81         intptr_t randomLocation = 0;
  82         randomLocation = arc4random() & ((1 << 25) - 1);
  83         randomLocation += (1 << 24);
  84         randomLocation <<= 21;
  85         result = reinterpret_cast<void*>(randomLocation);
  86     }
  87 #endif
  88
  89     result = mmap(result, bytes, protection, flags, fd, 0);
  90     if (result == MAP_FAILED) {
  91     #if ENABLE(INTERPRETER)
  92         if (executable)
  93             result = 0;
  94         else
  95     #endif
  96             CRASH();
  97     }
  98     if (result && includesGuardPages) {
  99         // We use mmap to remap the guardpages rather than using mprotect as
 100         // mprotect results in multiple references to the code region.  This
 101         // breaks the madvise based mechanism we use to return physical memory
 102         // to the OS.
 103         mmap(result, pageSize(), PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON, fd, 0);
 104         mmap(static_cast<char*>(result) + bytes - pageSize(), pageSize(), PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON, fd, 0);
 105     }
 106
 107     return result;
 108 }
 109
 110 void OSAllocator::commit(void* address, size_t bytes, bool, bool)
 111 {
 112 #if HAVE(MADV_FREE_REUSE)
 113     while (madvise(address, bytes, MADV_FREE_REUSE) == -1 && errno == EAGAIN) { }
 114 #else
 115     // Non-MADV_FREE_REUSE reservations automatically commit on demand.
 116     UNUSED_PARAM(address);
 117     UNUSED_PARAM(bytes);
 118 #endif
 119 }
 120
 121 void OSAllocator::decommit(void* address, size_t bytes)
 122 {
 123 #if HAVE(MADV_FREE_REUSE)
 124     while (madvise(address, bytes, MADV_FREE_REUSABLE) == -1 && errno == EAGAIN) { }
 125 #elif HAVE(MADV_FREE)
 126     while (madvise(address, bytes, MADV_FREE) == -1 && errno == EAGAIN) { }
 127 #elif HAVE(MADV_DONTNEED)
 128     while (madvise(address, bytes, MADV_DONTNEED) == -1 && errno == EAGAIN) { }
 129 #else
 130     UNUSED_PARAM(address);
 131     UNUSED_PARAM(bytes);
 132 #endif
 133 }
 134
 135 void OSAllocator::releaseDecommitted(void* address, size_t bytes)
 136 {
 137     int result = munmap(address, bytes);
 138     if (result == -1)
 139         CRASH();
 140 }
 141
 142 } // namespace WTF