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- // Copyright 2019 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_IMMEDIATE_CRASH_H_
- #define BASE_IMMEDIATE_CRASH_H_
- #include "build/build_config.h"
- // Crashes in the fastest possible way with no attempt at logging.
- // There are several constraints; see http://crbug.com/664209 for more context.
- //
- // - TRAP_SEQUENCE_() must be fatal. It should not be possible to ignore the
- // resulting exception or simply hit 'continue' to skip over it in a debugger.
- // - Different instances of TRAP_SEQUENCE_() must not be folded together, to
- // ensure crash reports are debuggable. Unlike __builtin_trap(), asm volatile
- // blocks will not be folded together.
- // Note: TRAP_SEQUENCE_() previously required an instruction with a unique
- // nonce since unlike clang, GCC folds together identical asm volatile
- // blocks.
- // - TRAP_SEQUENCE_() must produce a signal that is distinct from an invalid
- // memory access.
- // - TRAP_SEQUENCE_() must be treated as a set of noreturn instructions.
- // __builtin_unreachable() is used to provide that hint here. clang also uses
- // this as a heuristic to pack the instructions in the function epilogue to
- // improve code density.
- //
- // Additional properties that are nice to have:
- // - TRAP_SEQUENCE_() should be as compact as possible.
- // - The first instruction of TRAP_SEQUENCE_() should not change, to avoid
- // shifting crash reporting clusters. As a consequence of this, explicit
- // assembly is preferred over intrinsics.
- // Note: this last bullet point may no longer be true, and may be removed in
- // the future.
- // Note: TRAP_SEQUENCE Is currently split into two macro helpers due to the fact
- // that clang emits an actual instruction for __builtin_unreachable() on certain
- // platforms (see https://crbug.com/958675). In addition, the int3/bkpt/brk will
- // be removed in followups, so splitting it up like this now makes it easy to
- // land the followups.
- #if defined(COMPILER_GCC)
- #if defined(OS_NACL)
- // Crash report accuracy is not guaranteed on NaCl.
- #define TRAP_SEQUENCE1_() __builtin_trap()
- #define TRAP_SEQUENCE2_() asm volatile("")
- #elif defined(ARCH_CPU_X86_FAMILY)
- // TODO(https://crbug.com/958675): In theory, it should be possible to use just
- // int3. However, there are a number of crashes with SIGILL as the exception
- // code, so it seems likely that there's a signal handler that allows execution
- // to continue after SIGTRAP.
- #define TRAP_SEQUENCE1_() asm volatile("int3")
- #if defined(OS_APPLE)
- // Intentionally empty: __builtin_unreachable() is always part of the sequence
- // (see IMMEDIATE_CRASH below) and already emits a ud2 on Mac.
- #define TRAP_SEQUENCE2_() asm volatile("")
- #else
- #define TRAP_SEQUENCE2_() asm volatile("ud2")
- #endif // defined(OS_APPLE)
- #elif defined(ARCH_CPU_ARMEL)
- // bkpt will generate a SIGBUS when running on armv7 and a SIGTRAP when running
- // as a 32 bit userspace app on arm64. There doesn't seem to be any way to
- // cause a SIGTRAP from userspace without using a syscall (which would be a
- // problem for sandboxing).
- // TODO(https://crbug.com/958675): Remove bkpt from this sequence.
- #define TRAP_SEQUENCE1_() asm volatile("bkpt #0")
- #define TRAP_SEQUENCE2_() asm volatile("udf #0")
- #elif defined(ARCH_CPU_ARM64)
- // This will always generate a SIGTRAP on arm64.
- // TODO(https://crbug.com/958675): Remove brk from this sequence.
- #define TRAP_SEQUENCE1_() asm volatile("brk #0")
- #define TRAP_SEQUENCE2_() asm volatile("hlt #0")
- #else
- // Crash report accuracy will not be guaranteed on other architectures, but at
- // least this will crash as expected.
- #define TRAP_SEQUENCE1_() __builtin_trap()
- #define TRAP_SEQUENCE2_() asm volatile("")
- #endif // ARCH_CPU_*
- #elif defined(COMPILER_MSVC)
- #if !defined(__clang__)
- // MSVC x64 doesn't support inline asm, so use the MSVC intrinsic.
- #define TRAP_SEQUENCE1_() __debugbreak()
- #define TRAP_SEQUENCE2_()
- #elif defined(ARCH_CPU_ARM64)
- // Windows ARM64 uses "BRK #F000" as its breakpoint instruction, and
- // __debugbreak() generates that in both VC++ and clang.
- #define TRAP_SEQUENCE1_() __debugbreak()
- // Intentionally empty: __builtin_unreachable() is always part of the sequence
- // (see IMMEDIATE_CRASH below) and already emits a ud2 on Win64,
- // https://crbug.com/958373
- #define TRAP_SEQUENCE2_() __asm volatile("")
- #else
- #define TRAP_SEQUENCE1_() asm volatile("int3")
- #define TRAP_SEQUENCE2_() asm volatile("ud2")
- #endif // __clang__
- #else
- #error No supported trap sequence!
- #endif // COMPILER_GCC
- #define TRAP_SEQUENCE_() \
- do { \
- TRAP_SEQUENCE1_(); \
- TRAP_SEQUENCE2_(); \
- } while (false)
- // CHECK() and the trap sequence can be invoked from a constexpr function.
- // This could make compilation fail on GCC, as it forbids directly using inline
- // asm inside a constexpr function. However, it allows calling a lambda
- // expression including the same asm.
- // The side effect is that the top of the stacktrace will not point to the
- // calling function, but to this anonymous lambda. This is still useful as the
- // full name of the lambda will typically include the name of the function that
- // calls CHECK() and the debugger will still break at the right line of code.
- #if !defined(COMPILER_GCC)
- #define WRAPPED_TRAP_SEQUENCE_() TRAP_SEQUENCE_()
- #else
- #define WRAPPED_TRAP_SEQUENCE_() \
- do { \
- [] { TRAP_SEQUENCE_(); }(); \
- } while (false)
- #endif // !defined(COMPILER_GCC)
- #if defined(__clang__) || defined(COMPILER_GCC)
- // __builtin_unreachable() hints to the compiler that this is noreturn and can
- // be packed in the function epilogue.
- #define IMMEDIATE_CRASH() \
- ({ \
- WRAPPED_TRAP_SEQUENCE_(); \
- __builtin_unreachable(); \
- })
- #else
- // This is supporting non-chromium user of logging.h to build with MSVC, like
- // pdfium. On MSVC there is no __builtin_unreachable().
- #define IMMEDIATE_CRASH() WRAPPED_TRAP_SEQUENCE_()
- #endif // defined(__clang__) || defined(COMPILER_GCC)
- #endif // BASE_IMMEDIATE_CRASH_H_
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