[wasm] Add guard regions to end of WebAssembly.Memory buffers

src/base/platform/platform-posix.cc

Index: src/base/platform/platform-posix.cc
diff --git a/src/base/platform/platform-posix.cc b/src/base/platform/platform-posix.cc
index 3f4165de536c1f2047fc40dc248fd2158413598f..cbce33f61ab0302752cb9e38c7276b9619463078 100644
--- a/src/base/platform/platform-posix.cc
+++ b/src/base/platform/platform-posix.cc
@@ -129,6 +129,15 @@ void OS::Guard(void* address, const size_t size) {
 #endif
 }
 
+// Make a region of memory readable and writable.
+void OS::Unprotect(void* address, const size_t size) {

[Michael Lippautz, 2016/10/27 14:41:50]

Maybe we should have OS::Protect as a dual function to OS::Unprotect. 
You could keep OS::Guard to just call OS:Protect.

[Eric Holk, 2016/10/28 16:20:13]

I think I'd probably do OS::Protect and take flags for read, write or execute to
have it basically mirror mprotect or VirtualProtect.

+#if V8_OS_CYGWIN
+  DWORD oldprotect;
+  VirtualProtect(address, size, PAGE_READWRITE, &oldprotect);
+#else
+  mprotect(address, size, PROT_READ | PROT_WRITE);
+#endif
+}
 
 static LazyInstance<RandomNumberGenerator>::type
     platform_random_number_generator = LAZY_INSTANCE_INITIALIZER;