1 // Copyright 2016 The Chromium Authors 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 PARTITION_ALLOC_SHIM_ALLOCATOR_SHIM_INTERNALS_H_ 6 #define PARTITION_ALLOC_SHIM_ALLOCATOR_SHIM_INTERNALS_H_ 7 8 #include "build/build_config.h" 9 10 #if defined(__GNUC__) 11 12 #if BUILDFLAG(IS_POSIX) 13 #include <sys/cdefs.h> // for __THROW 14 #endif 15 16 #ifndef __THROW // Not a glibc system 17 #ifdef _NOEXCEPT // LLVM libc++ uses noexcept instead 18 #define __THROW _NOEXCEPT 19 #else 20 #define __THROW 21 #endif // !_NOEXCEPT 22 #endif 23 24 // Shim layer symbols need to be ALWAYS exported, regardless of component build. 25 // 26 // If an exported symbol is linked into a DSO, it may be preempted by a 27 // definition in the main executable. If this happens to an allocator symbol, it 28 // will mean that the DSO will use the main executable's allocator. This is 29 // normally relatively harmless -- regular allocations should all use the same 30 // allocator, but if the DSO tries to hook the allocator it will not see any 31 // allocations. 32 // 33 // However, if LLVM LTO is enabled, the compiler may inline the shim layer 34 // symbols into callers. The end result is that allocator calls in DSOs may use 35 // either the main executable's allocator or the DSO's allocator, depending on 36 // whether the call was inlined. This is arguably a bug in LLVM caused by its 37 // somewhat irregular handling of symbol interposition (see llvm.org/PR23501). 38 // To work around the bug we use noinline to prevent the symbols from being 39 // inlined. 40 // 41 // In the long run we probably want to avoid linking the allocator bits into 42 // DSOs altogether. This will save a little space and stop giving DSOs the false 43 // impression that they can hook the allocator. 44 #define SHIM_ALWAYS_EXPORT __attribute__((visibility("default"), noinline)) 45 46 #elif BUILDFLAG(IS_WIN) // __GNUC__ 47 48 #define __THROW 49 #define SHIM_ALWAYS_EXPORT __declspec(noinline) 50 51 #endif // __GNUC__ 52 53 #endif // PARTITION_ALLOC_SHIM_ALLOCATOR_SHIM_INTERNALS_H_ 54