mac: Hook up allocator shim.

base/allocator/allocator_shim_override_mac_symbols.h

+// Copyright 2016 The Chromium Authors. All rights reserved.

[Primiano Tucci (use gerrit), 2017/01/17 17:09:59]

s/2016/2017/ happy new year :)
also I think this file is mixing together the shim entry and exit point.
If you look at the other platforms, there are two sets of files in the shim
usually:
1) allocator_shim_override_XXX.h
2) allocator_shim_default_dispatch_to_YYY.cc

1 is the entrypoint, essentially the magical mechanism that make it so that when
something in chrome calls malloc & friend, that call is diverted to the shim.
From what I see here, this is the case here for InitializeAllocatorShim, 
ShimZoneCallbacks, etc

2 is the exit point. After the chain of dispatchers has been traversed, this
file defines how to go back to the actual malloc implementation (the last link
of the chain). This is the case here for the definition of
AllocatorDispatch::default_dispatch
and the various MallocImpl* etc

I'd keep 1 and 2 separate, mostly for the sake of keeping the pattern of the
shim consistent. It's already quite complicated as you can see, I'd avoid adding
more entropy :)

Now, I am aware that the tricky part here is that there is a dependency on the
two. Essentially when you initialize the shim you retrieve and save the old
methods in that g_unshimmed_zone and than use that after the dispatch.
The best way that comes to my mind is to follow the pattern that siggi followed
on Win, which is creating a separate .cc file (see win_stubs) which is used by
both.

This also links to the other comment that I have  about memory_mac.mm

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This header defines symbols to override the same functions in the Visual C++
+// CRT implementation.
+
+#ifdef BASE_ALLOCATOR_ALLOCATOR_SHIM_OVERRIDE_MAC_SYMBOLS_H_
+#error This header is meant to be included only once by allocator_shim.cc
+#endif
+#define BASE_ALLOCATOR_ALLOCATOR_SHIM_OVERRIDE_MAC_SYMBOLS_H_
+
+#include <pthread.h>
+#include <mach/mach.h>
+#include <mach/mach_vm.h>
+#include <malloc/malloc.h>
+
+#include "base/logging.h"
+#include "base/mac/mach_logging.h"
+#include "base/process/memory.h"
+#include "third_party/apple_apsl/malloc.h"
+
+namespace {
+
+using base::allocator::AllocatorDispatch;
+
+ChromeMallocZone g_unshimmed_zone;
+
+template <class F, class... Args>
+auto CallUnshimmed(F ChromeMallocZone::*m, Args... args)
+    -> decltype(std::declval<F>()(nullptr, args...)) {
+  F f = g_unshimmed_zone.*m
+            ? g_unshimmed_zone.*m
+            : reinterpret_cast<ChromeMallocZone*>(malloc_default_zone())->*m;
+  return f(malloc_default_zone(), args...);
+}
+
+void* MallocImpl(const AllocatorDispatch*, size_t size) {
+  return CallUnshimmed(&ChromeMallocZone::malloc, size);
+}
+
+void* CallocImpl(const AllocatorDispatch*, size_t n, size_t size) {
+  return CallUnshimmed(&ChromeMallocZone::calloc, n, size);
+}
+
+void* MemalignImpl(const AllocatorDispatch*, size_t alignment, size_t size) {
+  ChromeMallocZone* defaul_zone =
+      reinterpret_cast<ChromeMallocZone*>(malloc_default_zone());
+  if (defaul_zone->version >= 5) {
+    return CallUnshimmed(&ChromeMallocZone::memalign, alignment, size);
+  } else if (alignment == GetCachedPageSize()) {
+    return CallUnshimmed(&ChromeMallocZone::valloc, size);
+  } else {
+    CHECK(false) << "memalign() is not implemented.";
+    return nullptr;
+  }
+}
+
+void* ReallocImpl(const AllocatorDispatch*, void* ptr, size_t size) {
+  return CallUnshimmed(&ChromeMallocZone::realloc, ptr, size);
+}
+
+void FreeImpl(const AllocatorDispatch*, void* ptr) {
+  CallUnshimmed(&ChromeMallocZone::free, ptr);
+}
+
+size_t GetSizeEstimateImpl(const AllocatorDispatch*, void* ptr) {
+  return CallUnshimmed(&ChromeMallocZone::size, ptr);
+}
+
+unsigned BatchMallocImpl(const AllocatorDispatch* self,
+                         size_t size,
+                         void** results,
+                         unsigned num_requested) {
+  return CallUnshimmed(&ChromeMallocZone::batch_malloc, size, results,
+                       num_requested);
+}
+
+void BatchFreeImpl(const AllocatorDispatch* self,
+                   void** to_be_freed,
+                   unsigned num_to_be_freed) {
+  CallUnshimmed(&ChromeMallocZone::batch_free, to_be_freed, num_to_be_freed);
+}
+
+void ShimZoneCallbacks(ChromeMallocZone* zone) {

[Primiano Tucci (use gerrit), 2017/01/17 17:09:59]

just for clarify I think should be called InitializeShimZoneCallbacks,
SetupShimZoneCallbacks  or similar

+  zone->size = [](malloc_zone_t* zone, const void* ptr) -> size_t {
+    return ShimGetSizeEstimate(ptr);
+  };
+  zone->malloc = [](malloc_zone_t* zone, size_t size) -> void* {
+    return ShimMalloc(size);
+  };
+  zone->calloc = [](malloc_zone_t* zone, size_t n, size_t size) -> void* {
+    return ShimCalloc(n, size);
+  };
+  zone->valloc = [](malloc_zone_t* zone, size_t size) -> void* {
+    return ShimValloc(size);
+  };
+  zone->free = [](malloc_zone_t* zone, void* ptr) { ShimFree(ptr); };
+  zone->realloc = [](malloc_zone_t* zone, void* ptr, size_t size) -> void* {
+    return ShimRealloc(ptr, size);
+  };
+  zone->batch_malloc = [](struct _malloc_zone_t* zone, size_t size,
+                          void** results, unsigned num_requested) -> unsigned {
+    return ShimBatchMalloc(size, results, num_requested);
+  };
+  zone->batch_free = [](struct _malloc_zone_t* zone, void** to_be_freed,
+                        unsigned num_to_be_freed) -> void {
+    ShimBatchFree(to_be_freed, num_to_be_freed);
+  };
+
+  if (zone->version >= 5) {
+    zone->memalign = [](malloc_zone_t* zone, size_t alignment,
+                        size_t size) -> void* {
+      return ShimMemalign(alignment, size);
+    };
+  }
+  if (zone->version >= 6) {
+    zone->free_definite_size = [](malloc_zone_t* zone, void* ptr, size_t size) {
+      ShimFree(ptr);
+    };
+  }
+}
+
+void InitializeAllocatorShim() {
+  ChromeMallocZone* default_zone =
+      reinterpret_cast<ChromeMallocZone*>(malloc_default_zone());
+
+  mach_vm_address_t default_reprotection_start = 0;
+  mach_vm_size_t default_reprotection_length = 0;
+  vm_prot_t default_reprotection_value = VM_PROT_NONE;
+  base::DeprotectMallocZone(default_zone, &default_reprotection_start,
+                            &default_reprotection_length,
+                            &default_reprotection_value);
+
+  CHECK(default_zone->size && default_zone->malloc && default_zone->calloc &&
+        default_zone->valloc && default_zone->free && default_zone->realloc)
+      << "Failed to get system allocation functions.";
+  g_unshimmed_zone.size = default_zone->size;
+  g_unshimmed_zone.malloc = default_zone->malloc;
+  g_unshimmed_zone.calloc = default_zone->calloc;
+  g_unshimmed_zone.valloc = default_zone->valloc;
+  g_unshimmed_zone.free = default_zone->free;
+  g_unshimmed_zone.realloc = default_zone->realloc;
+  g_unshimmed_zone.batch_malloc = default_zone->batch_malloc;
+  g_unshimmed_zone.batch_free = default_zone->batch_free;
+
+  g_unshimmed_zone.version = default_zone->version;
+  if (default_zone->version >= 5) {
+    g_unshimmed_zone.memalign = default_zone->memalign;
+  }
+  if (default_zone->version >= 6) {
+    g_unshimmed_zone.free_definite_size = default_zone->free_definite_size;
+  }
+
+  ShimZoneCallbacks(default_zone);
+
+  if (default_reprotection_start) {
+    kern_return_t result = mach_vm_protect(
+        mach_task_self(), default_reprotection_start,
+        default_reprotection_length, false, default_reprotection_value);
+    MACH_CHECK(result == KERN_SUCCESS, result) << "mach_vm_protect";
+  }
+}
+
+__attribute__((constructor)) void InitializeAllocatorShimAtDlOpen() {
+  InitializeAllocatorShim();

[Primiano Tucci (use gerrit), 2017/01/17 17:09:59]

Hmm this:
- will cause the static initializers check to go red on the main waterfall and
revert the cl
- is a bit too magical. If I read the current code correctly, it is all
initialized by EnableTerminationOnOutOfMemory(), which is called in
content_main_runner.cc. Can we keep th same pattern, i.e. create an explicit
InitializeAllocatorShim() api in allocator_shim.h and call it from
content_main_runner.cc
- concretely this might open new bugs that we were not exposed before because we
call this too early

+}
+
+}  // namespace
+
+const AllocatorDispatch AllocatorDispatch::default_dispatch = {
+    &MallocImpl,          /* alloc_function */
+    &CallocImpl,          /* alloc_zero_initialized_function */
+    &MemalignImpl,        /* alloc_aligned_function */
+    &ReallocImpl,         /* realloc_function */
+    &FreeImpl,            /* free_function */
+    &GetSizeEstimateImpl, /* get_size_estimate_function */
+    &BatchMallocImpl,     /* batch_malloc_function */
+    &BatchFreeImpl,       /* batch_free_function */
+    nullptr,              /* next */
+};