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v8: loosen artificial mmap constraint

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Fixes #4010.
This commit is contained in:
Bryan Cantrill 2012-09-18 15:35:29 -07:00 committed by isaacs
parent 0400571676
commit 4165f736e6
1 changed files with 13 additions and 4 deletions
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17
deps/v8/src/platform-posix.cc vendored
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@ -109,11 +109,20 @@ void* OS::GetRandomMmapAddr() {
raw_addr &= V8_UINT64_C(0x3ffffffff000);
#else
uint32_t raw_addr = V8::RandomPrivate(isolate);
// The range 0x20000000 - 0x60000000 is relatively unpopulated across a
// variety of ASLR modes (PAE kernel, NX compat mode, etc) and on macos
// 10.6 and 10.7.
// For our 32-bit mmap() hint, we pick a random address in the bottom
// half of the top half of the address space (that is, the third quarter).
// Because we do not MAP_FIXED, this will be treated only as a hint -- the
// system will not fail to mmap() because something else happens to already
// be mapped at our random address. We deliberately set the hint high enough
// to get well above the system's break (that is, the heap); systems will
// either try the hint and if that fails move higher (MacOS and other BSD
// derivatives) or try the hint and if that fails allocate as if there were
// no hint at all (Linux, Solaris, illumos and derivatives). The high hint
// prevents the break from getting hemmed in at low values, ceding half of
// the address space to the system heap.
raw_addr &= 0x3ffff000;
raw_addr += 0x20000000;
raw_addr += 0x80000000;
#endif
return reinterpret_cast<void*>(raw_addr);
}