Allocator shim skeleton + Linux impl behind a build flag

base/allocator/allocator_shim.h

Index: base/allocator/allocator_shim.h
diff --git a/base/allocator/allocator_shim.h b/base/allocator/allocator_shim.h
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_ALLOCATOR_ALLOCATOR_SHIM_H_
+#define BASE_ALLOCATOR_ALLOCATOR_SHIM_H_
+
+#include <stddef.h>
+
+#include "base/base_export.h"
+
+namespace base {
+namespace allocator {
+
+// Allocator Shim API. Allows to to:
+//  - Configure the behavior of the allocator (what to do on OOM failures).
+//  - Install new hooks (AllocatorDispatch) in the allocator chain.
+
+// When this shim layer is enabled, the route of an allocation is as-follows:
+//
+// [allocator_shim_override_*.h] Intercept malloc() / operator new calls:
+//   The override_* headers define the symbols required to intercept calls to
+//   malloc() and operator new (if not overridden by specific C++ classes).
+//
+// [allocator_shim.cc] Routing allocation calls to the shim:
+//   The headers above route the calls to the internal ShimMalloc(), ShimFree(),
+//   ShimCppNew() etc. methods defined in allocator_shim.cc.
+//   These methods will: (1) forward the allocation call to the front of the
+//   AllocatorDispatch chain. (2) perform security hardenings (e.g., might
+//   call std::new_handler on OOM failure).
+//
+// [allocator_shim_default_dispatch_to_*.cc] The AllocatorDispatch chain:
+//   It is a singly linked list where each element is a struct with function
+//   pointers (|malloc_function|, |free_function|, etc). Normally the chain
+//   consists of a single AllocatorDispatch element, herein called
+//   the "default dispatch", which is statically defined at build time and
+//   ultimately routes the calls to the actual allocator defined by the build
+//   config (tcmalloc, glibc, ...).
+//
+// It is possible to dynamically insert further AllocatorDispatch stages
+// to the front of the chain, for debugging / profiling purposes.
+//
+// All the functions must be thred safe. The shim does not enforce any
+// serialization. This is to route to thread-aware allocators (e.g, tcmalloc)
+// wihout introducing unnecessary perf hits.
+
+struct AllocatorDispatch {
+  using AllocFn = void*(const AllocatorDispatch* self, size_t size);
+  using AllocZeroInitializedFn = void*(const AllocatorDispatch* self,
+                                       size_t n,
+                                       size_t size);
+  using AllocAlignedFn = void*(const AllocatorDispatch* self,
+                               size_t alignment,
+                               size_t size);
+  using ReallocFn = void*(const AllocatorDispatch* self,
+                          void* address,
+                          size_t size);
+  using FreeFn = void(const AllocatorDispatch* self, void* address);
+
+  AllocFn* const alloc_function;
+  AllocZeroInitializedFn* const alloc_zero_initialized_function;
+  AllocAlignedFn* const alloc_aligned_function;
+  ReallocFn* const realloc_function;
+  FreeFn* const free_function;
+
+  const AllocatorDispatch* next;
+
+  // |default_dispatch| is statically defined by one (and only one) of the
+  // allocator_shim_default_dispatch_to_*.cc files, depending on the build
+  // configuration.
+  static const AllocatorDispatch default_dispatch;
+};
+
+// When true makes malloc behave like new, w.r.t calling the new_handler if
+// the allocation fails (see set_new_mode() in Windows).
+BASE_EXPORT void SetCallNewHandlerOnMallocFailure(bool value);
+
+// Allocates |size| bytes or returns nullptr. It does NOT call the new_handler,
+// regardless of SetCallNewHandlerOnMallocFailure().
+BASE_EXPORT void* UncheckedAlloc(size_t size);
+
+// Inserts |dispatch| in front of the allocator chain. This method is NOT
+// thread-safe w.r.t concurrent invocations of InsertAllocatorDispatch().
+// The callers have the responsibility of linearizing the changes to the chain
+// (or more likely call these always on the same thread).
+BASE_EXPORT void InsertAllocatorDispatch(AllocatorDispatch* dispatch);
+
+// Test-only. Rationale: (1) lack of use cases; (2) dealing safely with a
+// removal of arbitrary elements from a singly linked list would require a lock
+// in malloc(), which we really don't want.
+BASE_EXPORT void RemoveAllocatorDispatchForTesting(AllocatorDispatch* dispatch);
+
+}  // namespace allocator
+}  // namespace base
+
+#endif  // BASE_ALLOCATOR_ALLOCATOR_SHIM_H_