Preserve OOM call stack entries

Partition Alloc has a few different out-of-memory error reporting paths
with different meanings for the "size" parameter. These different paths
are supposed to be distinguishable by looking at the call stack but a
combination of code folding and tail-call optimizations means that this
is not actually guaranteed. In one (most?) crash dumps a call to
PartitionOutOfMemoryWithLargeVirtualSize shows up on the stack as a call
to PartitionExcessiveAllocationSize.

This change disables code folding for the relevant functions, and
disables tail calls as well.

This should make understanding OOM failures easier.

Bug: 1159694
Change-Id: I0faf577fa0e82e88f7a06940c97a570e778e5ec8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2607585
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Will Harris <wfh@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Auto-Submit: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840248}

base/allocator/partition_allocator/oom.h

@@ -6,6 +6,7 @@
 #define BASE_ALLOCATOR_PARTITION_ALLOCATOR_OOM_H_
 
 #include "base/allocator/partition_allocator/oom_callback.h"
+#include "base/compiler_specific.h"
 #include "base/process/memory.h"
 #include "build/build_config.h"
 
@@ -15,8 +16,9 @@
 
 namespace {
 // The crash is generated in a NOINLINE function so that we can classify the
-// crash as an OOM solely by analyzing the stack trace.
-[[noreturn]] NOINLINE void OnNoMemory(size_t size) {
+// crash as an OOM solely by analyzing the stack trace. It is tagged as
+// NOT_TAIL_CALLED to ensure that its parent function stays on the stack.
+[[noreturn]] NOINLINE void NOT_TAIL_CALLED OnNoMemory(size_t size) {
   base::internal::RunPartitionAllocOomCallback();
   base::internal::OnNoMemoryInternal(size);
   IMMEDIATE_CRASH();

base/allocator/partition_allocator/partition_oom.cc

@@ -5,6 +5,8 @@
 #include "base/allocator/partition_allocator/partition_oom.h"
 
 #include "base/allocator/partition_allocator/oom.h"
+#include "base/compiler_specific.h"
+#include "base/debug/alias.h"
 #include "build/build_config.h"
 
 namespace base {
@@ -12,17 +14,27 @@ namespace internal {
 
 OomFunction g_oom_handling_function = nullptr;
 
-void NOINLINE PartitionExcessiveAllocationSize(size_t size) {
+NOINLINE void NOT_TAIL_CALLED PartitionExcessiveAllocationSize(size_t size) {
+  // Prevent code folding.
+  const int line_number = __LINE__;
+  base::debug::Alias(&line_number);
   OOM_CRASH(size);
 }
 
 #if !defined(ARCH_CPU_64_BITS)
-NOINLINE void PartitionOutOfMemoryWithLotsOfUncommitedPages(size_t size) {
+NOINLINE void NOT_TAIL_CALLED
+PartitionOutOfMemoryWithLotsOfUncommitedPages(size_t size) {
+  // Prevent code folding.
+  const int line_number = __LINE__;
+  base::debug::Alias(&line_number);
   OOM_CRASH(size);
 }
 
-[[noreturn]] NOINLINE void PartitionOutOfMemoryWithLargeVirtualSize(
-    size_t virtual_size) {
+[[noreturn]] NOINLINE void NOT_TAIL_CALLED
+PartitionOutOfMemoryWithLargeVirtualSize(size_t virtual_size) {
+  // Prevent code folding.
+  const int line_number = __LINE__;
+  base::debug::Alias(&line_number);
   OOM_CRASH(virtual_size);
 }