Allocator shim skeleton + Linux impl behind a build flag

base/allocator/allocator_shim.cc

+// 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.
+
+#include "base/allocator/allocator_shim.h"
+
+#include <errno.h>
+#include <unistd.h>
+
+#include <new>
+
+#include "base/atomicops.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/threading/platform_thread.h"
+#include "build/build_config.h"
+
+// No calls to malloc / new in this file. They would would cause re-entrancy of
+// the shim, which is hard to deal with. Keep this code as simple as possible
+// and don't use any external C++ object here, not even //base ones. Even if
+// they are safe to use today, in future they might be refactored.
+
+namespace {
+
+using namespace base;
+
+const allocator::AllocatorDispatch* g_chain_head =
+    &allocator::AllocatorDispatch::default_dispatch;
+
+bool g_call_new_handler_on_malloc_failure = false;
+subtle::Atomic32 g_new_handler_lock = 0;
+
+// In theory this should be just base::ThreadChecker. But we can't afford
+// the luxury of a LazyInstance<ThreadChecker> here as it would cause a new().
+bool CalledOnValidThread() {
+  static PlatformThreadId thread_id = kInvalidThreadId;
+  if (thread_id == kInvalidThreadId)
+    thread_id = PlatformThread::CurrentId();
+  return thread_id == PlatformThread::CurrentId();
+}
+
+inline size_t GetPageSize() {
+  static size_t pagesize = 0;
+  if (!pagesize)
+    pagesize = sysconf(_SC_PAGESIZE);
+  return pagesize;
+}
+
+// Calls the std::new handler thread-safely. Returns true if a new_handler was
+// set and called, false if no new_handler was set.
+bool CallNewHandler() {
+  // TODO(primiano): C++11 has introduced ::get_new_handler() which is supposed
+  // to be thread safe and would avoid the spinlock boilerplate here. However
+  // it doesn't seem to be available yet in the Linux chroot headers yet.
+  std::new_handler nh;
+  {
+    while (subtle::Acquire_CompareAndSwap(&g_new_handler_lock, 0, 1))
+      PlatformThread::YieldCurrentThread();
+    nh = std::set_new_handler(0);
+    ignore_result(std::set_new_handler(nh));
+    subtle::Release_Store(&g_new_handler_lock, 0);
+  }
+  if (!nh)
+    return false;
+  (*nh)();
+  return true;  // Assume the new_handler will abort if it fails.
+}
+
+}  // namespace
+
+namespace base {
+namespace allocator {
+
+void SetCallNewHandlerOnMallocFailure(bool value) {
+  g_call_new_handler_on_malloc_failure = value;
+}
+
+void* UncheckedAlloc(size_t size) {
+  return g_chain_head->alloc_function(size, g_chain_head);
+}
+
+void InsertAllocatorDispatch(AllocatorDispatch* dispatch) {
+  // Ensure this (and Remove below) are always called on the same thread.
+  DCHECK(CalledOnValidThread());
+
+  dispatch->next = g_chain_head;

[Primiano Tucci (use gerrit), 2016/02/16 22:58:06]

Ok, this I think is going to be the most controversial part of the CL.
The overall good news is that in production code this is never going to be hit,
this is really to install the tracing hooks. But it's not a good reason for not
making it future-proof.
I know that here I am plain on danger zone as:
 - writing pointers is not guaranteed to be atomic (but AFAIK they actually are
on all the platforms we care about)
- There is a memory barrier betweens the writes here, but no barrier on the
read. My rationale here is that the readers has a data dependency: you need to
get the head pointer (g_chain_head) in order to get the next pointer, so if they
are written in order, it shouldn't be possible for the hw itself to read them in
the reverse order.
- my biggest doubt is about compiler optimizations: the lack of read barriers
might allow the compiler to reorder the reads. the read here is just
dereferencing g_chain_head but here my knowledge on what the compiler might do
or not decays here.

+
+  // This function does not guarantee to be thread-safe w.r.t. concurrent
+  // insertion / removals, but still has to guarantee that all the threads
+  // always see a consistent chain, hence the MemoryBarrier() below.
+  // InsertAllocatorDispatch() is NOT a fastpath, as opposite to malloc(), so
+  // we don't really want this to be a release-store with a corresponding
+  // acquire-load during malloc().
+  base::subtle::MemoryBarrier();
+
+  g_chain_head = dispatch;
+}
+
+void RemoveAllocatorDispatch(AllocatorDispatch* dispatch) {
+  DCHECK(CalledOnValidThread());
+  g_chain_head = dispatch->next;
+}
+
+}  // namespace allocator
+}  // namespace base
+
+// THe Shim* functions below are the entry-points into the shim-layer and
+// are supposed to be invoked / aliased by the allocator_shim_override_*
+// headers to route the malloc / new symbols through the shim layer.
+extern "C" {
+
+// The general pattern for allocations is:
+// - Try to allocate, if succeded return the pointer.
+// - If the allocation failed:
+//   - Call the std::new_handler if it was a C++ allocation.
+//   - Call the std::new_handler if it was a malloc() (or calloc() or similar)
+//     AND SetCallNewHandlerOnMallocFailure(true).
+//   - If the std::new_handler is NOT set just return nullptr.
+//   - If the std::new_handler is set:
+//     - Assume it will abort() if it fails (very likely the new_handler will
+//       just suicide priting a message).
+//     - Assume it did succeed if it returns, in which case reattempt the alloc.
+
+void* ShimCppNew(size_t size) {
+  void* ptr;
+  do {
+    ptr = g_chain_head->alloc_function(size, g_chain_head);
+  } while (!ptr && CallNewHandler());
+  return ptr;
+}
+
+void ShimCppDelete(void* address) {
+  return g_chain_head->free_function(address, g_chain_head);
+}
+
+void* ShimMalloc(size_t size) {
+  void* ptr;
+  do {
+    ptr = g_chain_head->alloc_function(size, g_chain_head);
+  } while (!ptr && g_call_new_handler_on_malloc_failure && CallNewHandler());
+  return ptr;
+}
+
+void* ShimCalloc(size_t n, size_t size) {
+  void* ptr;
+  do {
+    ptr = g_chain_head->alloc_zero_initialized_function(n, size, g_chain_head);
+  } while (!ptr && g_call_new_handler_on_malloc_failure && CallNewHandler());
+  return ptr;
+}
+
+void* ShimRealloc(void* address, size_t size) {
+  // realloc(size == 0) means free() and might return a nullptr. We should
+  // not call the std::new_handler in that case, though.
+  void* ptr;
+  do {
+    ptr = g_chain_head->realloc_function(address, size, g_chain_head);
+  } while (!ptr && size && g_call_new_handler_on_malloc_failure &&
+           CallNewHandler());
+  return ptr;
+}
+
+void* ShimMemalign(size_t alignment, size_t size) {
+  void* ptr;
+  do {
+    ptr = g_chain_head->alloc_aligned_function(alignment, size, g_chain_head);
+  } while (!ptr && g_call_new_handler_on_malloc_failure && CallNewHandler());
+  return ptr;
+}
+
+int ShimPosixMemalign(void** res, size_t alignment, size_t size) {
+  // posix_memalign is supposed to check the arguments. See tc_posix_memalign()
+  // in tc_malloc.cc.
+  if (((alignment % sizeof(void*)) != 0) ||
+      ((alignment & (alignment - 1)) != 0) || (alignment == 0)) {
+    return EINVAL;
+  }
+  void* ptr = ShimMemalign(alignment, size);
+  *res = ptr;
+  return ptr ? 0 : ENOMEM;
+}
+
+void* ShimValloc(size_t size) {
+  return ShimMemalign(GetPageSize(), size);
+}
+
+void* ShimPvalloc(size_t size) {
+  // pvalloc(0) should allocate one page, according to its man page.
+  if (size == 0) {
+    size = GetPageSize();
+  } else {
+    size = (size + GetPageSize() - 1) & ~(GetPageSize() - 1);
+  }
+  return ShimMemalign(GetPageSize(), size);
+}
+
+void ShimFree(void* address) {
+  return g_chain_head->free_function(address, g_chain_head);
+}
+
+}  // extern "C"
+
+// Cpp symbols (new / delete) should always be routed through the shim layer.
+#include "base/allocator/allocator_shim_override_cpp_symbols.h"
+
+// Ditto for plain malloc() / calloc() / free() etc. symbols.
+#include "base/allocator/allocator_shim_override_libc_symbols.h"
+
+// In the case of tcmalloc we also want to plumb into the glibc hooks
+// to avoid that allocations made in glibc itself (e.g., strdup()) get
+// accidentally performed on the glibc heap instead of the tcmalloc one.
+#if defined(USE_TCMALLOC)
+#include "base/allocator/allocator_shim_override_glibc_weak_symbols.h"
+#endif
+
+// Cross-checks.
+
+#if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
+#error The allocator shim should not be compiled when building for memory tools.
+#endif
+
+#if (defined(__GNUC__) && defined(__EXCEPTIONS)) || \
+    (defined(_HAS_EXCEPTIONS) && _HAS_EXCEPTIONS)
+#error This code cannot be used when exceptions are turned on.
+#endif