Disable variable initialization in sandbox_nt_util.cc

This is working version of crrev.com/c/1966357
Previous fix does not work.

Bug: 977230
Change-Id: I859e57856bd7fb07b7587f8f80f08c7feb24b69a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1973353
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Reviewed-by: Alex Gough <ajgo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728833}

sandbox/win/src/sandbox_nt_util.cc

@@ -9,6 +9,7 @@
 
 #include <string>
 
+#include "base/compiler_specific.h"
 #include "base/win/pe_image.h"
 #include "sandbox/win/src/sandbox_factory.h"
 #include "sandbox/win/src/target_services.h"
@@ -58,18 +59,8 @@ void* AllocateNearTo(void* source, size_t size) {
   const char* top_address = base + kMaxSize;
 
   while (base < top_address) {
-    // Initialize all fields to avoid memset with init_stack_vars = true.
-    // "= {}" or  -ftrivial-auto-var-init=pattern may insert memset or memcpy
-    // here. However if memset was used here even "init_stack_vars = false
-    // is_debug = true" on x86_64 crashes in GPU process.
-    MEMORY_BASIC_INFORMATION mem_info;
-    mem_info.BaseAddress = nullptr;
-    mem_info.AllocationBase = nullptr;
-    mem_info.AllocationProtect = 0;
-    mem_info.RegionSize = 0;
-    mem_info.State = 0;
-    mem_info.Protect = 0;
-    mem_info.Type = 0;
+    // Avoid memset inserted by -ftrivial-auto-var-init=pattern.
+    STACK_UNINITIALIZED MEMORY_BASIC_INFORMATION mem_info;
     NTSTATUS status =
         g_nt.QueryVirtualMemory(NtCurrentProcess, base, MemoryBasicInformation,
                                 &mem_info, sizeof(mem_info), nullptr);