1 // Copyright 2019 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.
5 #ifndef BASE_IMMEDIATE_CRASH_H_
6 #define BASE_IMMEDIATE_CRASH_H_
8 #include "build/build_config.h"
10 // Crashes in the fastest possible way with no attempt at logging.
11 // There are several constraints; see http://crbug.com/664209 for more context.
13 // - TRAP_SEQUENCE_() must be fatal. It should not be possible to ignore the
14 // resulting exception or simply hit 'continue' to skip over it in a debugger.
15 // - Different instances of TRAP_SEQUENCE_() must not be folded together, to
16 // ensure crash reports are debuggable. Unlike __builtin_trap(), asm volatile
17 // blocks will not be folded together.
18 // Note: TRAP_SEQUENCE_() previously required an instruction with a unique
19 // nonce since unlike clang, GCC folds together identical asm volatile
21 // - TRAP_SEQUENCE_() must produce a signal that is distinct from an invalid
23 // - TRAP_SEQUENCE_() must be treated as a set of noreturn instructions.
24 // __builtin_unreachable() is used to provide that hint here. clang also uses
25 // this as a heuristic to pack the instructions in the function epilogue to
26 // improve code density.
28 // Additional properties that are nice to have:
29 // - TRAP_SEQUENCE_() should be as compact as possible.
30 // - The first instruction of TRAP_SEQUENCE_() should not change, to avoid
31 // shifting crash reporting clusters. As a consequence of this, explicit
32 // assembly is preferred over intrinsics.
33 // Note: this last bullet point may no longer be true, and may be removed in
36 // Note: TRAP_SEQUENCE Is currently split into two macro helpers due to the fact
37 // that clang emits an actual instruction for __builtin_unreachable() on certain
38 // platforms (see https://crbug.com/958675). In addition, the int3/bkpt/brk will
39 // be removed in followups, so splitting it up like this now makes it easy to
40 // land the followups.
42 #if defined(COMPILER_GCC)
46 // Crash report accuracy is not guaranteed on NaCl.
47 #define TRAP_SEQUENCE1_() __builtin_trap()
48 #define TRAP_SEQUENCE2_() asm volatile("")
50 #elif defined(ARCH_CPU_X86_FAMILY)
52 // TODO(https://crbug.com/958675): In theory, it should be possible to use just
53 // int3. However, there are a number of crashes with SIGILL as the exception
54 // code, so it seems likely that there's a signal handler that allows execution
55 // to continue after SIGTRAP.
56 #define TRAP_SEQUENCE1_() asm volatile("int3")
58 #if defined(OS_MACOSX)
59 // Intentionally empty: __builtin_unreachable() is always part of the sequence
60 // (see IMMEDIATE_CRASH below) and already emits a ud2 on Mac.
61 #define TRAP_SEQUENCE2_() asm volatile("")
63 #define TRAP_SEQUENCE2_() asm volatile("ud2")
64 #endif // defined(OS_MACOSX)
66 #elif defined(ARCH_CPU_ARMEL)
68 // bkpt will generate a SIGBUS when running on armv7 and a SIGTRAP when running
69 // as a 32 bit userspace app on arm64. There doesn't seem to be any way to
70 // cause a SIGTRAP from userspace without using a syscall (which would be a
71 // problem for sandboxing).
72 // TODO(https://crbug.com/958675): Remove bkpt from this sequence.
73 #define TRAP_SEQUENCE1_() asm volatile("bkpt #0")
74 #define TRAP_SEQUENCE2_() asm volatile("udf #0")
76 #elif defined(ARCH_CPU_ARM64)
78 // This will always generate a SIGTRAP on arm64.
79 // TODO(https://crbug.com/958675): Remove brk from this sequence.
80 #define TRAP_SEQUENCE1_() asm volatile("brk #0")
81 #define TRAP_SEQUENCE2_() asm volatile("hlt #0")
85 // Crash report accuracy will not be guaranteed on other architectures, but at
86 // least this will crash as expected.
87 #define TRAP_SEQUENCE1_() __builtin_trap()
88 #define TRAP_SEQUENCE2_() asm volatile("")
92 #elif defined(COMPILER_MSVC)
94 #if !defined(__clang__)
96 // MSVC x64 doesn't support inline asm, so use the MSVC intrinsic.
97 #define TRAP_SEQUENCE1_() __debugbreak()
98 #define TRAP_SEQUENCE2_()
100 #elif defined(ARCH_CPU_ARM64)
102 // Windows ARM64 uses "BRK #F000" as its breakpoint instruction, and
103 // __debugbreak() generates that in both VC++ and clang.
104 #define TRAP_SEQUENCE1_() __debugbreak()
105 // Intentionally empty: __builtin_unreachable() is always part of the sequence
106 // (see IMMEDIATE_CRASH below) and already emits a ud2 on Win64,
107 // https://crbug.com/958373
108 #define TRAP_SEQUENCE2_() __asm volatile("")
112 #define TRAP_SEQUENCE1_() asm volatile("int3")
113 #define TRAP_SEQUENCE2_() asm volatile("ud2")
119 #error No supported trap sequence!
121 #endif // COMPILER_GCC
123 #define TRAP_SEQUENCE_() \
129 // CHECK() and the trap sequence can be invoked from a constexpr function.
130 // This could make compilation fail on GCC, as it forbids directly using inline
131 // asm inside a constexpr function. However, it allows calling a lambda
132 // expression including the same asm.
133 // The side effect is that the top of the stacktrace will not point to the
134 // calling function, but to this anonymous lambda. This is still useful as the
135 // full name of the lambda will typically include the name of the function that
136 // calls CHECK() and the debugger will still break at the right line of code.
137 #if !defined(COMPILER_GCC)
139 #define WRAPPED_TRAP_SEQUENCE_() TRAP_SEQUENCE_()
143 #define WRAPPED_TRAP_SEQUENCE_() \
145 [] { TRAP_SEQUENCE_(); }(); \
148 #endif // !defined(COMPILER_GCC)
150 #if defined(__clang__) || defined(COMPILER_GCC)
152 // __builtin_unreachable() hints to the compiler that this is noreturn and can
153 // be packed in the function epilogue.
154 #define IMMEDIATE_CRASH() \
156 WRAPPED_TRAP_SEQUENCE_(); \
157 __builtin_unreachable(); \
162 // This is supporting non-chromium user of logging.h to build with MSVC, like
163 // pdfium. On MSVC there is no __builtin_unreachable().
164 #define IMMEDIATE_CRASH() WRAPPED_TRAP_SEQUENCE_()
166 #endif // defined(__clang__) || defined(COMPILER_GCC)
168 #endif // BASE_IMMEDIATE_CRASH_H_