diff --git a/deps/v8/src/platform-posix.cc b/deps/v8/src/platform-posix.cc index 0016d59d3a7..e652a083cdc 100644 --- a/deps/v8/src/platform-posix.cc +++ b/deps/v8/src/platform-posix.cc @@ -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(raw_addr); }