JavaScriptCore-903.tar.gz

[apple/javascriptcore.git] / wtf / OSAllocatorPosix.cpp

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