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27 #include "OSAllocator.h"
29 #include "PageAllocation.h"
32 #include <wtf/Assertions.h>
33 #include <wtf/UnusedParam.h>
37 void* OSAllocator::reserveUncommitted(size_t bytes, Usage usage, bool writable, bool executable, bool includesGuardPages)
40 // Reserve memory with PROT_NONE and MAP_LAZY so it isn't committed now.
41 void* result = mmap(0, bytes, PROT_NONE, MAP_LAZY | MAP_PRIVATE | MAP_ANON, -1, 0);
42 if (result == MAP_FAILED)
46 void* result = reserveAndCommit(bytes, usage, writable, executable, includesGuardPages);
48 madvise(result, bytes, MADV_DONTNEED);
49 #elif HAVE(MADV_FREE_REUSE)
50 // To support the "reserve then commit" model, we have to initially decommit.
51 while (madvise(result, bytes, MADV_FREE_REUSABLE) == -1 && errno == EAGAIN) { }
59 void* OSAllocator::reserveAndCommit(size_t bytes, Usage usage, bool writable, bool executable, bool includesGuardPages)
61 // All POSIX reservations start out logically committed.
62 int protection = PROT_READ;
64 protection |= PROT_WRITE;
66 protection |= PROT_EXEC;
68 int flags = MAP_PRIVATE | MAP_ANON;
74 #if (OS(LINUX) && CPU(X86_64))
75 // Linux distros usually do not allow overcommit by default, so
76 // JSC's strategy of mmaping a large amount of memory upfront
77 // won't work very well on some systems. Fortunately there's a
78 // flag we can pass to mmap to disable the overcommit check for
79 // this particular call, so we can get away with it as long as the
80 // overcommit flag value in /proc/sys/vm/overcommit_memory is 0
81 // ('heuristic') and not 2 (always check). 0 is the usual default
82 // value, so this should work well in general.
83 flags |= MAP_NORESERVE;
93 #if (OS(DARWIN) && CPU(X86_64))
95 ASSERT(includesGuardPages);
96 // Cook up an address to allocate at, using the following recipe:
97 // 17 bits of zero, stay in userspace kids.
98 // 26 bits of randomness for ASLR.
99 // 21 bits of zero, at least stay aligned within one level of the pagetables.
101 // But! - as a temporary workaround for some plugin problems (rdar://problem/6812854),
102 // for now instead of 2^26 bits of ASLR lets stick with 25 bits of randomization plus
103 // 2^24, which should put up somewhere in the middle of userspace (in the address range
104 // 0x200000000000 .. 0x5fffffffffff).
105 intptr_t randomLocation = 0;
106 randomLocation = arc4random() & ((1 << 25) - 1);
107 randomLocation += (1 << 24);
108 randomLocation <<= 21;
109 result = reinterpret_cast<void*>(randomLocation);
113 result = mmap(result, bytes, protection, flags, fd, 0);
114 if (result == MAP_FAILED) {
115 #if ENABLE(CLASSIC_INTERPRETER) || ENABLE(LLINT)
122 if (result && includesGuardPages) {
123 // We use mmap to remap the guardpages rather than using mprotect as
124 // mprotect results in multiple references to the code region. This
125 // breaks the madvise based mechanism we use to return physical memory
127 mmap(result, pageSize(), PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON, fd, 0);
128 mmap(static_cast<char*>(result) + bytes - pageSize(), pageSize(), PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANON, fd, 0);
133 void OSAllocator::commit(void* address, size_t bytes, bool writable, bool executable)
136 int protection = PROT_READ;
138 protection |= PROT_WRITE;
140 protection |= PROT_EXEC;
141 if (MAP_FAILED == mmap(address, bytes, protection, MAP_FIXED | MAP_PRIVATE | MAP_ANON, -1, 0))
144 UNUSED_PARAM(writable);
145 UNUSED_PARAM(executable);
146 madvise(address, bytes, MADV_WILLNEED);
147 #elif HAVE(MADV_FREE_REUSE)
148 UNUSED_PARAM(writable);
149 UNUSED_PARAM(executable);
150 while (madvise(address, bytes, MADV_FREE_REUSE) == -1 && errno == EAGAIN) { }
152 // Non-MADV_FREE_REUSE reservations automatically commit on demand.
153 UNUSED_PARAM(address);
155 UNUSED_PARAM(writable);
156 UNUSED_PARAM(executable);
160 void OSAllocator::decommit(void* address, size_t bytes)
163 // Use PROT_NONE and MAP_LAZY to decommit the pages.
164 mmap(address, bytes, PROT_NONE, MAP_FIXED | MAP_LAZY | MAP_PRIVATE | MAP_ANON, -1, 0);
166 madvise(address, bytes, MADV_DONTNEED);
167 #elif HAVE(MADV_FREE_REUSE)
168 while (madvise(address, bytes, MADV_FREE_REUSABLE) == -1 && errno == EAGAIN) { }
169 #elif HAVE(MADV_FREE)
170 while (madvise(address, bytes, MADV_FREE) == -1 && errno == EAGAIN) { }
171 #elif HAVE(MADV_DONTNEED)
172 while (madvise(address, bytes, MADV_DONTNEED) == -1 && errno == EAGAIN) { }
174 UNUSED_PARAM(address);
179 void OSAllocator::releaseDecommitted(void* address, size_t bytes)
181 int result = munmap(address, bytes);