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comparison: mfbt/Assertions.h

mfbt/Assertions.h

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1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 /* This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6
7 /* Implementations of runtime and static assertion macros for C and C++. */
8
9 #ifndef mozilla_Assertions_h
10 #define mozilla_Assertions_h
11
12 #include "mozilla/Attributes.h"
13 #include "mozilla/Compiler.h"
14 #include "mozilla/Likely.h"
15 #include "mozilla/MacroArgs.h"
16
17 #include <stddef.h>
18 #include <stdio.h>
19 #include <stdlib.h>
20 #ifdef WIN32
21 /*
22 * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
23 * further depends on <windef.h>. We hardcode these few definitions manually
24 * because those headers clutter the global namespace with a significant
25 * number of undesired macros and symbols.
26 */
27 # ifdef __cplusplus
28 extern "C" {
29 # endif
30 __declspec(dllimport) int __stdcall
31 TerminateProcess(void* hProcess, unsigned int uExitCode);
32 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
33 # ifdef __cplusplus
34 }
35 # endif
36 #else
37 # include <signal.h>
38 #endif
39 #ifdef ANDROID
40 # include <android/log.h>
41 #endif
42
43 /*
44 * MOZ_STATIC_ASSERT may be used to assert a condition *at compile time* in C.
45 * In C++11, static_assert is provided by the compiler to the same effect.
46 * This can be useful when you make certain assumptions about what must hold for
47 * optimal, or even correct, behavior. For example, you might assert that the
48 * size of a struct is a multiple of the target architecture's word size:
49 *
50 * struct S { ... };
51 * // C
52 * MOZ_STATIC_ASSERT(sizeof(S) % sizeof(size_t) == 0,
53 * "S should be a multiple of word size for efficiency");
54 * // C++11
55 * static_assert(sizeof(S) % sizeof(size_t) == 0,
56 * "S should be a multiple of word size for efficiency");
57 *
58 * This macro can be used in any location where both an extern declaration and a
59 * typedef could be used.
60 */
61 #ifndef __cplusplus
62 /*
63 * Some of the definitions below create an otherwise-unused typedef. This
64 * triggers compiler warnings with some versions of gcc, so mark the typedefs
65 * as permissibly-unused to disable the warnings.
66 */
67 # if defined(__GNUC__)
68 # define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE __attribute__((unused))
69 # else
70 # define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE /* nothing */
71 # endif
72 # define MOZ_STATIC_ASSERT_GLUE1(x, y) x##y
73 # define MOZ_STATIC_ASSERT_GLUE(x, y) MOZ_STATIC_ASSERT_GLUE1(x, y)
74 # if defined(__SUNPRO_CC)
75 /*
76 * The Sun Studio C++ compiler is buggy when declaring, inside a function,
77 * another extern'd function with an array argument whose length contains a
78 * sizeof, triggering the error message "sizeof expression not accepted as
79 * size of array parameter". This bug (6688515, not public yet) would hit
80 * defining moz_static_assert as a function, so we always define an extern
81 * array for Sun Studio.
82 *
83 * We include the line number in the symbol name in a best-effort attempt
84 * to avoid conflicts (see below).
85 */
86 # define MOZ_STATIC_ASSERT(cond, reason) \
87 extern char MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)[(cond) ? 1 : -1]
88 # elif defined(__COUNTER__)
89 /*
90 * If there was no preferred alternative, use a compiler-agnostic version.
91 *
92 * Note that the non-__COUNTER__ version has a bug in C++: it can't be used
93 * in both |extern "C"| and normal C++ in the same translation unit. (Alas
94 * |extern "C"| isn't allowed in a function.) The only affected compiler
95 * we really care about is gcc 4.2. For that compiler and others like it,
96 * we include the line number in the function name to do the best we can to
97 * avoid conflicts. These should be rare: a conflict would require use of
98 * MOZ_STATIC_ASSERT on the same line in separate files in the same
99 * translation unit, *and* the uses would have to be in code with
100 * different linkage, *and* the first observed use must be in C++-linkage
101 * code.
102 */
103 # define MOZ_STATIC_ASSERT(cond, reason) \
104 typedef int MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __COUNTER__)[(cond) ? 1 : -1] MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
105 # else
106 # define MOZ_STATIC_ASSERT(cond, reason) \
107 extern void MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)(int arg[(cond) ? 1 : -1]) MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
108 # endif
109
110 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason) MOZ_STATIC_ASSERT(!(cond) || (expr), reason)
111 #else
112 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason) static_assert(!(cond) || (expr), reason)
113 #endif
114
115 #ifdef __cplusplus
116 extern "C" {
117 #endif
118
119 /*
120 * Prints |s| as an assertion failure (using file and ln as the location of the
121 * assertion) to the standard debug-output channel.
122 *
123 * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method. This
124 * method is primarily for internal use in this header, and only secondarily
125 * for use in implementing release-build assertions.
126 */
127 static MOZ_ALWAYS_INLINE void
128 MOZ_ReportAssertionFailure(const char* s, const char* file, int ln)
129 {
130 #ifdef ANDROID
131 __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
132 "Assertion failure: %s, at %s:%d\n", s, file, ln);
133 #else
134 fprintf(stderr, "Assertion failure: %s, at %s:%d\n", s, file, ln);
135 fflush(stderr);
136 #endif
137 }
138
139 static MOZ_ALWAYS_INLINE void
140 MOZ_ReportCrash(const char* s, const char* file, int ln)
141 {
142 #ifdef ANDROID
143 __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
144 "Hit MOZ_CRASH(%s) at %s:%d\n", s, file, ln);
145 #else
146 fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", s, file, ln);
147 fflush(stderr);
148 #endif
149 }
150
151 /**
152 * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH(). You should
153 * call MOZ_CRASH instead.
154 */
155 #if defined(_MSC_VER)
156 /*
157 * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
158 * (not nested in a system function) breakpoint. This distinctively invokes
159 * Breakpad without requiring system library symbols on all stack-processing
160 * machines, as a nested breakpoint would require.
161 *
162 * We use TerminateProcess with the exit code aborting would generate
163 * because we don't want to invoke atexit handlers, destructors, library
164 * unload handlers, and so on when our process might be in a compromised
165 * state.
166 *
167 * We don't use abort() because it'd cause Windows to annoyingly pop up the
168 * process error dialog multiple times. See bug 345118 and bug 426163.
169 *
170 * We follow TerminateProcess() with a call to MOZ_NoReturn() so that the
171 * compiler doesn't hassle us to provide a return statement after a
172 * MOZ_REALLY_CRASH() call.
173 *
174 * (Technically these are Windows requirements, not MSVC requirements. But
175 * practically you need MSVC for debugging, and we only ship builds created
176 * by MSVC, so doing it this way reduces complexity.)
177 */
178
179 __declspec(noreturn) __inline void MOZ_NoReturn() {}
180
181 # ifdef __cplusplus
182 # define MOZ_REALLY_CRASH() \
183 do { \
184 ::__debugbreak(); \
185 *((volatile int*) NULL) = 123; \
186 ::TerminateProcess(::GetCurrentProcess(), 3); \
187 ::MOZ_NoReturn(); \
188 } while (0)
189 # else
190 # define MOZ_REALLY_CRASH() \
191 do { \
192 __debugbreak(); \
193 *((volatile int*) NULL) = 123; \
194 TerminateProcess(GetCurrentProcess(), 3); \
195 MOZ_NoReturn(); \
196 } while (0)
197 # endif
198 #else
199 # ifdef __cplusplus
200 # define MOZ_REALLY_CRASH() \
201 do { \
202 *((volatile int*) NULL) = 123; \
203 ::abort(); \
204 } while (0)
205 # else
206 # define MOZ_REALLY_CRASH() \
207 do { \
208 *((volatile int*) NULL) = 123; \
209 abort(); \
210 } while (0)
211 # endif
212 #endif
213
214 /*
215 * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
216 * Breakpad-compatible way, in both debug and release builds.
217 *
218 * MOZ_CRASH is a good solution for "handling" failure cases when you're
219 * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
220 * corruption, and so on. It's also a good solution if you need safe behavior
221 * in release builds as well as debug builds. But if the failure is one that
222 * should be debugged and fixed, MOZ_ASSERT is generally preferable.
223 *
224 * The optional explanation-string, if provided, must be a string literal
225 * explaining why we're crashing. This argument is intended for use with
226 * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
227 * obvious why we're crashing.
228 *
229 * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
230 * explanation-string, we print the string to stderr. Otherwise, we don't
231 * print anything; this is because we want MOZ_CRASH to be 100% safe in release
232 * builds, and it's hard to print to stderr safely when memory might have been
233 * corrupted.
234 */
235 #ifndef DEBUG
236 # define MOZ_CRASH(...) MOZ_REALLY_CRASH()
237 #else
238 # define MOZ_CRASH(...) \
239 do { \
240 MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__); \
241 MOZ_REALLY_CRASH(); \
242 } while(0)
243 #endif
244
245 #ifdef __cplusplus
246 } /* extern "C" */
247 #endif
248
249 /*
250 * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
251 * debug builds. If it is, execution continues. Otherwise, an error message
252 * including the expression and the explanation-string (if provided) is printed,
253 * an attempt is made to invoke any existing debugger, and execution halts.
254 * MOZ_ASSERT is fatal: no recovery is possible. Do not assert a condition
255 * which can correctly be falsy.
256 *
257 * The optional explanation-string, if provided, must be a string literal
258 * explaining the assertion. It is intended for use with assertions whose
259 * correctness or rationale is non-obvious, and for assertions where the "real"
260 * condition being tested is best described prosaically. Don't provide an
261 * explanation if it's not actually helpful.
262 *
263 * // No explanation needed: pointer arguments often must not be NULL.
264 * MOZ_ASSERT(arg);
265 *
266 * // An explanation can be helpful to explain exactly how we know an
267 * // assertion is valid.
268 * MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
269 * "given that <thingA> and <thingB>, we must have...");
270 *
271 * // Or it might disambiguate multiple identical (save for their location)
272 * // assertions of the same expression.
273 * MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
274 * "we already set [[PrimitiveThis]] for this Boolean object");
275 * MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
276 * "we already set [[PrimitiveThis]] for this String object");
277 *
278 * MOZ_ASSERT has no effect in non-debug builds. It is designed to catch bugs
279 * *only* during debugging, not "in the field". If you want the latter, use
280 * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
281 */
282
283 /* First the single-argument form. */
284 #define MOZ_ASSERT_HELPER1(expr) \
285 do { \
286 if (MOZ_UNLIKELY(!(expr))) { \
287 MOZ_ReportAssertionFailure(#expr, __FILE__, __LINE__); \
288 MOZ_REALLY_CRASH(); \
289 } \
290 } while (0)
291 /* Now the two-argument form. */
292 #define MOZ_ASSERT_HELPER2(expr, explain) \
293 do { \
294 if (MOZ_UNLIKELY(!(expr))) { \
295 MOZ_ReportAssertionFailure(#expr " (" explain ")", __FILE__, __LINE__); \
296 MOZ_REALLY_CRASH(); \
297 } \
298 } while (0)
299
300 #define MOZ_RELEASE_ASSERT_GLUE(a, b) a b
301 #define MOZ_RELEASE_ASSERT(...) \
302 MOZ_RELEASE_ASSERT_GLUE( \
303 MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
304 (__VA_ARGS__))
305
306 #ifdef DEBUG
307 # define MOZ_ASSERT(...) MOZ_RELEASE_ASSERT(__VA_ARGS__)
308 #else
309 # define MOZ_ASSERT(...) do { } while(0)
310 #endif /* DEBUG */
311
312 /*
313 * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
314 * true.
315 *
316 * MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
317 *
318 * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds. It is
319 * designed to catch bugs during debugging, not "in the field".
320 */
321 #ifdef DEBUG
322 # define MOZ_ASSERT_IF(cond, expr) \
323 do { \
324 if (cond) \
325 MOZ_ASSERT(expr); \
326 } while (0)
327 #else
328 # define MOZ_ASSERT_IF(cond, expr) do { } while (0)
329 #endif
330
331 /*
332 * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that it is
333 * undefined behavior for execution to reach this point. No guarantees are made
334 * about what will happen if this is reached at runtime. Most code should
335 * probably use the higher level MOZ_ASSUME_UNREACHABLE, which uses this when
336 * appropriate.
337 */
338 #if defined(__clang__)
339 # define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
340 #elif defined(__GNUC__)
341 /*
342 * __builtin_unreachable() was implemented in gcc 4.5. If we don't have
343 * that, call a noreturn function; abort() will do nicely. Qualify the call
344 * in C++ in case there's another abort() visible in local scope.
345 */
346 # if MOZ_GCC_VERSION_AT_LEAST(4, 5, 0)
347 # define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
348 # else
349 # ifdef __cplusplus
350 # define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
351 # else
352 # define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
353 # endif
354 # endif
355 #elif defined(_MSC_VER)
356 # define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
357 #else
358 # ifdef __cplusplus
359 # define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
360 # else
361 # define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
362 # endif
363 #endif
364
365 /*
366 * MOZ_ASSUME_UNREACHABLE([reason]) tells the compiler that it can assume that
367 * the macro call cannot be reached during execution. This lets the compiler
368 * generate better-optimized code under some circumstances, at the expense of
369 * the program's behavior being undefined if control reaches the
370 * MOZ_ASSUME_UNREACHABLE.
371 *
372 * In Gecko, you probably should not use this macro outside of performance- or
373 * size-critical code, because it's unsafe. If you don't care about code size
374 * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
375 *
376 * SpiderMonkey is a different beast, and there it's acceptable to use
377 * MOZ_ASSUME_UNREACHABLE more widely.
378 *
379 * Note that MOZ_ASSUME_UNREACHABLE is noreturn, so it's valid not to return a
380 * value following a MOZ_ASSUME_UNREACHABLE call.
381 *
382 * Example usage:
383 *
384 * enum ValueType {
385 * VALUE_STRING,
386 * VALUE_INT,
387 * VALUE_FLOAT
388 * };
389 *
390 * int ptrToInt(ValueType type, void* value) {
391 * {
392 * // We know for sure that type is either INT or FLOAT, and we want this
393 * // code to run as quickly as possible.
394 * switch (type) {
395 * case VALUE_INT:
396 * return *(int*) value;
397 * case VALUE_FLOAT:
398 * return (int) *(float*) value;
399 * default:
400 * MOZ_ASSUME_UNREACHABLE("can only handle VALUE_INT and VALUE_FLOAT");
401 * }
402 * }
403 */
404 #if defined(DEBUG)
405 # define MOZ_ASSUME_UNREACHABLE(...) \
406 do { \
407 MOZ_ASSERT(false, "MOZ_ASSUME_UNREACHABLE(" __VA_ARGS__ ")"); \
408 MOZ_ASSUME_UNREACHABLE_MARKER(); \
409 } while (0)
410 #else
411 # define MOZ_ASSUME_UNREACHABLE(reason) MOZ_ASSUME_UNREACHABLE_MARKER()
412 #endif
413
414 /*
415 * MOZ_ALWAYS_TRUE(expr) and MOZ_ALWAYS_FALSE(expr) always evaluate the provided
416 * expression, in debug builds and in release builds both. Then, in debug
417 * builds only, the value of the expression is asserted either true or false
418 * using MOZ_ASSERT.
419 */
420 #ifdef DEBUG
421 # define MOZ_ALWAYS_TRUE(expr) MOZ_ASSERT((expr))
422 # define MOZ_ALWAYS_FALSE(expr) MOZ_ASSERT(!(expr))
423 #else
424 # define MOZ_ALWAYS_TRUE(expr) ((void)(expr))
425 # define MOZ_ALWAYS_FALSE(expr) ((void)(expr))
426 #endif
427
428 #endif /* mozilla_Assertions_h */

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