1 // Copyright 2016 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_ALLOCATOR_ALLOCATOR_SHIM_INTERNALS_H_ 6 #define BASE_ALLOCATOR_ALLOCATOR_SHIM_INTERNALS_H_ 7 8 #if defined(__GNUC__) 9 10 #include <sys/cdefs.h> // for __THROW 11 12 #ifndef __THROW // Not a glibc system 13 #ifdef _NOEXCEPT // LLVM libc++ uses noexcept instead 14 #define __THROW _NOEXCEPT 15 #else 16 #define __THROW 17 #endif // !_NOEXCEPT 18 #endif 19 20 // Shim layer symbols need to be ALWAYS exported, regardless of component build. 21 // 22 // If an exported symbol is linked into a DSO, it may be preempted by a 23 // definition in the main executable. If this happens to an allocator symbol, it 24 // will mean that the DSO will use the main executable's allocator. This is 25 // normally relatively harmless -- regular allocations should all use the same 26 // allocator, but if the DSO tries to hook the allocator it will not see any 27 // allocations. 28 // 29 // However, if LLVM LTO is enabled, the compiler may inline the shim layer 30 // symbols into callers. The end result is that allocator calls in DSOs may use 31 // either the main executable's allocator or the DSO's allocator, depending on 32 // whether the call was inlined. This is arguably a bug in LLVM caused by its 33 // somewhat irregular handling of symbol interposition (see llvm.org/PR23501). 34 // To work around the bug we use noinline to prevent the symbols from being 35 // inlined. 36 // 37 // In the long run we probably want to avoid linking the allocator bits into 38 // DSOs altogether. This will save a little space and stop giving DSOs the false 39 // impression that they can hook the allocator. 40 #define SHIM_ALWAYS_EXPORT __attribute__((visibility("default"), noinline)) 41 42 #endif // __GNUC__ 43 44 #endif // BASE_ALLOCATOR_ALLOCATOR_SHIM_INTERNALS_H_ 45