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* Copyright (C) 2010 Apple Inc. All rights reserved.
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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* THE POSSIBILITY OF SUCH DAMAGE.
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#include "OSAllocator.h"
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#include "PageAllocation.h"
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#include <wtf/Assertions.h>
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#include <wtf/UnusedParam.h>
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void* OSAllocator::reserveUncommitted(size_t bytes, Usage usage, bool writable, bool executable, bool includesGuardPages)
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// Reserve memory with PROT_NONE and MAP_LAZY so it isn't committed now.
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void* result = mmap(0, bytes, PROT_NONE, MAP_LAZY | MAP_PRIVATE | MAP_ANON, -1, 0);
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if (result == MAP_FAILED)
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void* result = reserveAndCommit(bytes, usage, writable, executable, includesGuardPages);
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madvise(result, bytes, MADV_DONTNEED);
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#elif HAVE(MADV_FREE_REUSE)
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// To support the "reserve then commit" model, we have to initially decommit.
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while (madvise(result, bytes, MADV_FREE_REUSABLE) == -1 && errno == EAGAIN) { }
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void* OSAllocator::reserveAndCommit(size_t bytes, Usage usage, bool writable, bool executable, bool includesGuardPages)
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// All POSIX reservations start out logically committed.
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int protection = PROT_READ;
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protection |= PROT_WRITE;
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protection |= PROT_EXEC;
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int flags = MAP_PRIVATE | MAP_ANON;
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#if (OS(LINUX) && CPU(X86_64))
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// Linux distros usually do not allow overcommit by default, so
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// JSC's strategy of mmaping a large amount of memory upfront
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// won't work very well on some systems. Fortunately there's a
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// flag we can pass to mmap to disable the overcommit check for
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// this particular call, so we can get away with it as long as the
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// overcommit flag value in /proc/sys/vm/overcommit_memory is 0
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// ('heuristic') and not 2 (always check). 0 is the usual default
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// value, so this should work well in general.
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flags |= MAP_NORESERVE;
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#if (OS(DARWIN) && CPU(X86_64))
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ASSERT(includesGuardPages);
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// Cook up an address to allocate at, using the following recipe:
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// 17 bits of zero, stay in userspace kids.
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// 26 bits of randomness for ASLR.
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// 21 bits of zero, at least stay aligned within one level of the pagetables.
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// But! - as a temporary workaround for some plugin problems (rdar://problem/6812854),
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// for now instead of 2^26 bits of ASLR lets stick with 25 bits of randomization plus
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// 2^24, which should put up somewhere in the middle of userspace (in the address range
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// 0x200000000000 .. 0x5fffffffffff).
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intptr_t randomLocation = 0;
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randomLocation = arc4random() & ((1 << 25) - 1);
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randomLocation += (1 << 24);
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randomLocation <<= 21;
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result = reinterpret_cast<void*>(randomLocation);
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result = mmap(result, bytes, protection, flags, fd, 0);
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if (result == MAP_FAILED) {
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if (result && includesGuardPages) {
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// We use mmap to remap the guardpages rather than using mprotect as
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// mprotect results in multiple references to the code region. This
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// breaks the madvise based mechanism we use to return physical memory
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mmap(result, pageSize(), PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON, fd, 0);
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mmap(static_cast<char*>(result) + bytes - pageSize(), pageSize(), PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON, fd, 0);
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void OSAllocator::commit(void* address, size_t bytes, bool writable, bool executable)
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int protection = PROT_READ;
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protection |= PROT_WRITE;
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protection |= PROT_EXEC;
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if (MAP_FAILED == mmap(address, bytes, protection, MAP_FIXED | MAP_PRIVATE | MAP_ANON, -1, 0))
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UNUSED_PARAM(writable);
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UNUSED_PARAM(executable);
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madvise(address, bytes, MADV_WILLNEED);
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#elif HAVE(MADV_FREE_REUSE)
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UNUSED_PARAM(writable);
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UNUSED_PARAM(executable);
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while (madvise(address, bytes, MADV_FREE_REUSE) == -1 && errno == EAGAIN) { }
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// Non-MADV_FREE_REUSE reservations automatically commit on demand.
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UNUSED_PARAM(address);
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UNUSED_PARAM(writable);
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UNUSED_PARAM(executable);
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void OSAllocator::decommit(void* address, size_t bytes)
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// Use PROT_NONE and MAP_LAZY to decommit the pages.
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mmap(address, bytes, PROT_NONE, MAP_FIXED | MAP_LAZY | MAP_PRIVATE | MAP_ANON, -1, 0);
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madvise(address, bytes, MADV_DONTNEED);
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#elif HAVE(MADV_FREE_REUSE)
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while (madvise(address, bytes, MADV_FREE_REUSABLE) == -1 && errno == EAGAIN) { }
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#elif HAVE(MADV_FREE)
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while (madvise(address, bytes, MADV_FREE) == -1 && errno == EAGAIN) { }
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#elif HAVE(MADV_DONTNEED)
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while (madvise(address, bytes, MADV_DONTNEED) == -1 && errno == EAGAIN) { }
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UNUSED_PARAM(address);
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void OSAllocator::releaseDecommitted(void* address, size_t bytes)
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int result = munmap(address, bytes);