// 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_INTERNALS_H_ #define BASE_ALLOCATOR_ALLOCATOR_SHIM_INTERNALS_H_ #include "build/build_config.h" #if defined(__GNUC__) #if BUILDFLAG(IS_POSIX) #include // for __THROW #endif #ifndef __THROW // Not a glibc system #ifdef _NOEXCEPT // LLVM libc++ uses noexcept instead #define __THROW _NOEXCEPT #else #define __THROW #endif // !_NOEXCEPT #endif // Shim layer symbols need to be ALWAYS exported, regardless of component build. // // If an exported symbol is linked into a DSO, it may be preempted by a // definition in the main executable. If this happens to an allocator symbol, it // will mean that the DSO will use the main executable's allocator. This is // normally relatively harmless -- regular allocations should all use the same // allocator, but if the DSO tries to hook the allocator it will not see any // allocations. // // However, if LLVM LTO is enabled, the compiler may inline the shim layer // symbols into callers. The end result is that allocator calls in DSOs may use // either the main executable's allocator or the DSO's allocator, depending on // whether the call was inlined. This is arguably a bug in LLVM caused by its // somewhat irregular handling of symbol interposition (see llvm.org/PR23501). // To work around the bug we use noinline to prevent the symbols from being // inlined. // // In the long run we probably want to avoid linking the allocator bits into // DSOs altogether. This will save a little space and stop giving DSOs the false // impression that they can hook the allocator. #define SHIM_ALWAYS_EXPORT __attribute__((visibility("default"), noinline)) #elif BUILDFLAG(IS_WIN) // __GNUC__ #define __THROW #define SHIM_ALWAYS_EXPORT __declspec(noinline) #endif // __GNUC__ #endif // BASE_ALLOCATOR_ALLOCATOR_SHIM_INTERNALS_H_