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 #if defined(MOZILLA_INTERNAL_API) && defined(__cplusplus)
13 #define MOZ_DUMP_ASSERTION_STACK
14 #endif
15
16 #include "mozilla/Attributes.h"
17 #include "mozilla/Compiler.h"
18 #include "mozilla/Likely.h"
19 #include "mozilla/MacroArgs.h"
20 #include "mozilla/StaticAnalysisFunctions.h"
21 #include "mozilla/Types.h"
22 #ifdef MOZ_DUMP_ASSERTION_STACK
23 #include "nsTraceRefcnt.h"
24 #endif
25
26 #if defined(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)
27 /*
28 * The crash reason set by MOZ_CRASH_ANNOTATE is consumed by the crash reporter
29 * if present. It is declared here (and defined in Assertions.cpp) to make it
30 * available to all code, even libraries that don't link with the crash reporter
31 * directly.
32 */
33 MOZ_BEGIN_EXTERN_C
34 extern MFBT_DATA const char* gMozCrashReason;
35 MOZ_END_EXTERN_C
36
37 static inline void
AnnotateMozCrashReason(const char * reason)38 AnnotateMozCrashReason(const char* reason)
39 {
40 gMozCrashReason = reason;
41 }
42 # define MOZ_CRASH_ANNOTATE(...) AnnotateMozCrashReason(__VA_ARGS__)
43 #else
44 # define MOZ_CRASH_ANNOTATE(...) do { /* nothing */ } while (0)
45 #endif
46
47 #include <stddef.h>
48 #include <stdio.h>
49 #include <stdlib.h>
50 #ifdef WIN32
51 /*
52 * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
53 * further depends on <windef.h>. We hardcode these few definitions manually
54 * because those headers clutter the global namespace with a significant
55 * number of undesired macros and symbols.
56 */
57 # ifdef __cplusplus
58 extern "C" {
59 # endif
60 __declspec(dllimport) int __stdcall
61 TerminateProcess(void* hProcess, unsigned int uExitCode);
62 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
63 # ifdef __cplusplus
64 }
65 # endif
66 #else
67 # include <signal.h>
68 #endif
69 #ifdef ANDROID
70 # include <android/log.h>
71 #endif
72
73 /*
74 * MOZ_STATIC_ASSERT may be used to assert a condition *at compile time* in C.
75 * In C++11, static_assert is provided by the compiler to the same effect.
76 * This can be useful when you make certain assumptions about what must hold for
77 * optimal, or even correct, behavior. For example, you might assert that the
78 * size of a struct is a multiple of the target architecture's word size:
79 *
80 * struct S { ... };
81 * // C
82 * MOZ_STATIC_ASSERT(sizeof(S) % sizeof(size_t) == 0,
83 * "S should be a multiple of word size for efficiency");
84 * // C++11
85 * static_assert(sizeof(S) % sizeof(size_t) == 0,
86 * "S should be a multiple of word size for efficiency");
87 *
88 * This macro can be used in any location where both an extern declaration and a
89 * typedef could be used.
90 */
91 #ifndef __cplusplus
92 /*
93 * Some of the definitions below create an otherwise-unused typedef. This
94 * triggers compiler warnings with some versions of gcc, so mark the typedefs
95 * as permissibly-unused to disable the warnings.
96 */
97 # if defined(__GNUC__)
98 # define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE __attribute__((unused))
99 # else
100 # define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE /* nothing */
101 # endif
102 # define MOZ_STATIC_ASSERT_GLUE1(x, y) x##y
103 # define MOZ_STATIC_ASSERT_GLUE(x, y) MOZ_STATIC_ASSERT_GLUE1(x, y)
104 # if defined(__SUNPRO_CC)
105 /*
106 * The Sun Studio C++ compiler is buggy when declaring, inside a function,
107 * another extern'd function with an array argument whose length contains a
108 * sizeof, triggering the error message "sizeof expression not accepted as
109 * size of array parameter". This bug (6688515, not public yet) would hit
110 * defining moz_static_assert as a function, so we always define an extern
111 * array for Sun Studio.
112 *
113 * We include the line number in the symbol name in a best-effort attempt
114 * to avoid conflicts (see below).
115 */
116 # define MOZ_STATIC_ASSERT(cond, reason) \
117 extern char MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)[(cond) ? 1 : -1]
118 # elif defined(__COUNTER__)
119 /*
120 * If there was no preferred alternative, use a compiler-agnostic version.
121 *
122 * Note that the non-__COUNTER__ version has a bug in C++: it can't be used
123 * in both |extern "C"| and normal C++ in the same translation unit. (Alas
124 * |extern "C"| isn't allowed in a function.) The only affected compiler
125 * we really care about is gcc 4.2. For that compiler and others like it,
126 * we include the line number in the function name to do the best we can to
127 * avoid conflicts. These should be rare: a conflict would require use of
128 * MOZ_STATIC_ASSERT on the same line in separate files in the same
129 * translation unit, *and* the uses would have to be in code with
130 * different linkage, *and* the first observed use must be in C++-linkage
131 * code.
132 */
133 # define MOZ_STATIC_ASSERT(cond, reason) \
134 typedef int MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __COUNTER__)[(cond) ? 1 : -1] MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
135 # else
136 # define MOZ_STATIC_ASSERT(cond, reason) \
137 extern void MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)(int arg[(cond) ? 1 : -1]) MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
138 # endif
139
140 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason) MOZ_STATIC_ASSERT(!(cond) || (expr), reason)
141 #else
142 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason) static_assert(!(cond) || (expr), reason)
143 #endif
144
145 #ifdef __cplusplus
146 extern "C" {
147 #endif
148
149 /*
150 * Prints |aStr| as an assertion failure (using aFilename and aLine as the
151 * location of the assertion) to the standard debug-output channel.
152 *
153 * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method. This
154 * method is primarily for internal use in this header, and only secondarily
155 * for use in implementing release-build assertions.
156 */
157 static MOZ_COLD MOZ_ALWAYS_INLINE void
MOZ_ReportAssertionFailure(const char * aStr,const char * aFilename,int aLine)158 MOZ_ReportAssertionFailure(const char* aStr, const char* aFilename, int aLine)
159 MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS
160 {
161 #ifdef ANDROID
162 __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
163 "Assertion failure: %s, at %s:%d\n",
164 aStr, aFilename, aLine);
165 #else
166 fprintf(stderr, "Assertion failure: %s, at %s:%d\n", aStr, aFilename, aLine);
167 #if defined (MOZ_DUMP_ASSERTION_STACK)
168 nsTraceRefcnt::WalkTheStack(stderr);
169 #endif
170 fflush(stderr);
171 #endif
172 }
173
174 static MOZ_COLD MOZ_ALWAYS_INLINE void
MOZ_ReportCrash(const char * aStr,const char * aFilename,int aLine)175 MOZ_ReportCrash(const char* aStr, const char* aFilename, int aLine)
176 MOZ_PRETEND_NORETURN_FOR_STATIC_ANALYSIS
177 {
178 #ifdef ANDROID
179 __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
180 "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
181 #else
182 fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", aStr, aFilename, aLine);
183 #if defined(MOZ_DUMP_ASSERTION_STACK)
184 nsTraceRefcnt::WalkTheStack(stderr);
185 #endif
186 fflush(stderr);
187 #endif
188 }
189
190 /**
191 * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH(). You should
192 * call MOZ_CRASH instead.
193 */
194 #if defined(_MSC_VER)
195 /*
196 * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
197 * (not nested in a system function) breakpoint. This distinctively invokes
198 * Breakpad without requiring system library symbols on all stack-processing
199 * machines, as a nested breakpoint would require.
200 *
201 * We use TerminateProcess with the exit code aborting would generate
202 * because we don't want to invoke atexit handlers, destructors, library
203 * unload handlers, and so on when our process might be in a compromised
204 * state.
205 *
206 * We don't use abort() because it'd cause Windows to annoyingly pop up the
207 * process error dialog multiple times. See bug 345118 and bug 426163.
208 *
209 * We follow TerminateProcess() with a call to MOZ_NoReturn() so that the
210 * compiler doesn't hassle us to provide a return statement after a
211 * MOZ_REALLY_CRASH() call.
212 *
213 * (Technically these are Windows requirements, not MSVC requirements. But
214 * practically you need MSVC for debugging, and we only ship builds created
215 * by MSVC, so doing it this way reduces complexity.)
216 */
217
MOZ_NoReturn()218 __declspec(noreturn) __inline void MOZ_NoReturn() {}
219
220 # ifdef __cplusplus
221 # define MOZ_REALLY_CRASH(line) \
222 do { \
223 ::__debugbreak(); \
224 *((volatile int*) NULL) = line; \
225 ::TerminateProcess(::GetCurrentProcess(), 3); \
226 ::MOZ_NoReturn(); \
227 } while (0)
228 # else
229 # define MOZ_REALLY_CRASH(line) \
230 do { \
231 __debugbreak(); \
232 *((volatile int*) NULL) = line; \
233 TerminateProcess(GetCurrentProcess(), 3); \
234 MOZ_NoReturn(); \
235 } while (0)
236 # endif
237 #else
238 # ifdef __cplusplus
239 # define MOZ_REALLY_CRASH(line) \
240 do { \
241 *((volatile int*) NULL) = line; \
242 ::abort(); \
243 } while (0)
244 # else
245 # define MOZ_REALLY_CRASH(line) \
246 do { \
247 *((volatile int*) NULL) = line; \
248 abort(); \
249 } while (0)
250 # endif
251 #endif
252
253 /*
254 * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
255 * Breakpad-compatible way, in both debug and release builds.
256 *
257 * MOZ_CRASH is a good solution for "handling" failure cases when you're
258 * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
259 * corruption, and so on. It's also a good solution if you need safe behavior
260 * in release builds as well as debug builds. But if the failure is one that
261 * should be debugged and fixed, MOZ_ASSERT is generally preferable.
262 *
263 * The optional explanation-string, if provided, must be a string literal
264 * explaining why we're crashing. This argument is intended for use with
265 * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
266 * obvious why we're crashing.
267 *
268 * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
269 * explanation-string, we print the string to stderr. Otherwise, we don't
270 * print anything; this is because we want MOZ_CRASH to be 100% safe in release
271 * builds, and it's hard to print to stderr safely when memory might have been
272 * corrupted.
273 */
274 #ifndef DEBUG
275 # define MOZ_CRASH(...) \
276 do { \
277 MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")"); \
278 MOZ_REALLY_CRASH(__LINE__); \
279 } while (0)
280 #else
281 # define MOZ_CRASH(...) \
282 do { \
283 MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__); \
284 MOZ_CRASH_ANNOTATE("MOZ_CRASH(" __VA_ARGS__ ")"); \
285 MOZ_REALLY_CRASH(__LINE__); \
286 } while (0)
287 #endif
288
289 /*
290 * MOZ_CRASH_UNSAFE_OOL(explanation-string) can be used if the explanation
291 * string cannot be a string literal (but no other processing needs to be done
292 * on it). A regular MOZ_CRASH() is preferred wherever possible, as passing
293 * arbitrary strings from a potentially compromised process is not without risk.
294 * If the string being passed is the result of a printf-style function,
295 * consider using MOZ_CRASH_UNSAFE_PRINTF instead.
296 */
297 #ifndef DEBUG
298 MFBT_API MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE void
299 MOZ_CrashOOL(int aLine, const char* aReason);
300 # define MOZ_CRASH_UNSAFE_OOL(reason) MOZ_CrashOOL(__LINE__, reason)
301 #else
302 MFBT_API MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE void
303 MOZ_CrashOOL(const char* aFilename, int aLine, const char* aReason);
304 # define MOZ_CRASH_UNSAFE_OOL(reason) MOZ_CrashOOL(__FILE__, __LINE__, reason)
305 #endif
306
307 static const size_t sPrintfMaxArgs = 4;
308 static const size_t sPrintfCrashReasonSize = 1024;
309
310 #ifndef DEBUG
311 MFBT_API MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(2, 3) void
312 MOZ_CrashPrintf(int aLine, const char* aFormat, ...);
313 # define MOZ_CALL_CRASH_PRINTF(format, ...) \
314 MOZ_CrashPrintf(__LINE__, format, __VA_ARGS__)
315 #else
316 MFBT_API MOZ_COLD MOZ_NORETURN MOZ_NEVER_INLINE MOZ_FORMAT_PRINTF(3, 4) void
317 MOZ_CrashPrintf(const char* aFilename, int aLine, const char* aFormat, ...);
318 # define MOZ_CALL_CRASH_PRINTF(format, ...) \
319 MOZ_CrashPrintf(__FILE__, __LINE__, format, __VA_ARGS__)
320 #endif
321
322 /*
323 * MOZ_CRASH_UNSAFE_PRINTF(format, arg1 [, args]) can be used when more
324 * information is desired than a string literal can supply. The caller provides
325 * a printf-style format string, which must be a string literal and between
326 * 1 and 4 additional arguments. A regular MOZ_CRASH() is preferred wherever
327 * possible, as passing arbitrary strings to printf from a potentially
328 * compromised process is not without risk.
329 */
330 #define MOZ_CRASH_UNSAFE_PRINTF(format, ...) \
331 do { \
332 MOZ_STATIC_ASSERT_VALID_ARG_COUNT(__VA_ARGS__); \
333 static_assert( \
334 MOZ_PASTE_PREFIX_AND_ARG_COUNT(, __VA_ARGS__) <= sPrintfMaxArgs, \
335 "Only up to 4 additional arguments are allowed!"); \
336 static_assert(sizeof(format) <= sPrintfCrashReasonSize, \
337 "The supplied format string is too long!"); \
338 MOZ_CALL_CRASH_PRINTF("" format, __VA_ARGS__); \
339 } while (0)
340
341 #ifdef __cplusplus
342 } /* extern "C" */
343 #endif
344
345 /*
346 * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
347 * debug builds. If it is, execution continues. Otherwise, an error message
348 * including the expression and the explanation-string (if provided) is printed,
349 * an attempt is made to invoke any existing debugger, and execution halts.
350 * MOZ_ASSERT is fatal: no recovery is possible. Do not assert a condition
351 * which can correctly be falsy.
352 *
353 * The optional explanation-string, if provided, must be a string literal
354 * explaining the assertion. It is intended for use with assertions whose
355 * correctness or rationale is non-obvious, and for assertions where the "real"
356 * condition being tested is best described prosaically. Don't provide an
357 * explanation if it's not actually helpful.
358 *
359 * // No explanation needed: pointer arguments often must not be NULL.
360 * MOZ_ASSERT(arg);
361 *
362 * // An explanation can be helpful to explain exactly how we know an
363 * // assertion is valid.
364 * MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
365 * "given that <thingA> and <thingB>, we must have...");
366 *
367 * // Or it might disambiguate multiple identical (save for their location)
368 * // assertions of the same expression.
369 * MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
370 * "we already set [[PrimitiveThis]] for this Boolean object");
371 * MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
372 * "we already set [[PrimitiveThis]] for this String object");
373 *
374 * MOZ_ASSERT has no effect in non-debug builds. It is designed to catch bugs
375 * *only* during debugging, not "in the field". If you want the latter, use
376 * MOZ_RELEASE_ASSERT, which applies to non-debug builds as well.
377 *
378 * MOZ_DIAGNOSTIC_ASSERT works like MOZ_RELEASE_ASSERT in Nightly/Aurora and
379 * MOZ_ASSERT in Beta/Release - use this when a condition is potentially rare
380 * enough to require real user testing to hit, but is not security-sensitive.
381 * This can cause user pain, so use it sparingly. If a MOZ_DIAGNOSTIC_ASSERT
382 * is firing, it should promptly be converted to a MOZ_ASSERT while the failure
383 * is being investigated, rather than letting users suffer.
384 */
385
386 /*
387 * Implement MOZ_VALIDATE_ASSERT_CONDITION_TYPE, which is used to guard against
388 * accidentally passing something unintended in lieu of an assertion condition.
389 */
390
391 #ifdef __cplusplus
392 # include "mozilla/TypeTraits.h"
393 namespace mozilla {
394 namespace detail {
395
396 template<typename T>
397 struct AssertionConditionType
398 {
399 typedef typename RemoveReference<T>::Type ValueT;
400 static_assert(!IsArray<ValueT>::value,
401 "Expected boolean assertion condition, got an array or a "
402 "string!");
403 static_assert(!IsFunction<ValueT>::value,
404 "Expected boolean assertion condition, got a function! Did "
405 "you intend to call that function?");
406 static_assert(!IsFloatingPoint<ValueT>::value,
407 "It's often a bad idea to assert that a floating-point number "
408 "is nonzero, because such assertions tend to intermittently "
409 "fail. Shouldn't your code gracefully handle this case instead "
410 "of asserting? Anyway, if you really want to do that, write an "
411 "explicit boolean condition, like !!x or x!=0.");
412
413 static const bool isValid = true;
414 };
415
416 } // namespace detail
417 } // namespace mozilla
418 # define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x) \
419 static_assert(mozilla::detail::AssertionConditionType<decltype(x)>::isValid, \
420 "invalid assertion condition")
421 #else
422 # define MOZ_VALIDATE_ASSERT_CONDITION_TYPE(x)
423 #endif
424
425 /* First the single-argument form. */
426 #define MOZ_ASSERT_HELPER1(expr) \
427 do { \
428 MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr); \
429 if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) { \
430 MOZ_ReportAssertionFailure(#expr, __FILE__, __LINE__); \
431 MOZ_CRASH_ANNOTATE("MOZ_RELEASE_ASSERT(" #expr ")"); \
432 MOZ_REALLY_CRASH(__LINE__); \
433 } \
434 } while (0)
435 /* Now the two-argument form. */
436 #define MOZ_ASSERT_HELPER2(expr, explain) \
437 do { \
438 MOZ_VALIDATE_ASSERT_CONDITION_TYPE(expr); \
439 if (MOZ_UNLIKELY(!MOZ_CHECK_ASSERT_ASSIGNMENT(expr))) { \
440 MOZ_ReportAssertionFailure(#expr " (" explain ")", __FILE__, __LINE__); \
441 MOZ_CRASH_ANNOTATE("MOZ_RELEASE_ASSERT(" #expr ") (" explain ")"); \
442 MOZ_REALLY_CRASH(__LINE__); \
443 } \
444 } while (0)
445
446 #define MOZ_RELEASE_ASSERT_GLUE(a, b) a b
447 #define MOZ_RELEASE_ASSERT(...) \
448 MOZ_RELEASE_ASSERT_GLUE( \
449 MOZ_PASTE_PREFIX_AND_ARG_COUNT(MOZ_ASSERT_HELPER, __VA_ARGS__), \
450 (__VA_ARGS__))
451
452 #ifdef DEBUG
453 # define MOZ_ASSERT(...) MOZ_RELEASE_ASSERT(__VA_ARGS__)
454 #else
455 # define MOZ_ASSERT(...) do { } while (0)
456 #endif /* DEBUG */
457
458 #ifdef RELEASE_OR_BETA
459 # define MOZ_DIAGNOSTIC_ASSERT MOZ_ASSERT
460 #else
461 # define MOZ_DIAGNOSTIC_ASSERT MOZ_RELEASE_ASSERT
462 #endif
463
464 /*
465 * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
466 * true.
467 *
468 * MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
469 *
470 * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds. It is
471 * designed to catch bugs during debugging, not "in the field".
472 */
473 #ifdef DEBUG
474 # define MOZ_ASSERT_IF(cond, expr) \
475 do { \
476 if (cond) { \
477 MOZ_ASSERT(expr); \
478 } \
479 } while (0)
480 #else
481 # define MOZ_ASSERT_IF(cond, expr) do { } while (0)
482 #endif
483
484 /*
485 * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that
486 * it is undefined behavior for execution to reach this point. No guarantees
487 * are made about what will happen if this is reached at runtime. Most code
488 * should use MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE because it has extra
489 * asserts.
490 */
491 #if defined(__clang__) || defined(__GNUC__)
492 # define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
493 #elif defined(_MSC_VER)
494 # define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
495 #else
496 # ifdef __cplusplus
497 # define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
498 # else
499 # define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
500 # endif
501 #endif
502
503 /*
504 * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE([reason]) tells the compiler that it
505 * can assume that the macro call cannot be reached during execution. This lets
506 * the compiler generate better-optimized code under some circumstances, at the
507 * expense of the program's behavior being undefined if control reaches the
508 * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE.
509 *
510 * In Gecko, you probably should not use this macro outside of performance- or
511 * size-critical code, because it's unsafe. If you don't care about code size
512 * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
513 *
514 * SpiderMonkey is a different beast, and there it's acceptable to use
515 * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE more widely.
516 *
517 * Note that MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE is noreturn, so it's valid
518 * not to return a value following a MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE
519 * call.
520 *
521 * Example usage:
522 *
523 * enum ValueType {
524 * VALUE_STRING,
525 * VALUE_INT,
526 * VALUE_FLOAT
527 * };
528 *
529 * int ptrToInt(ValueType type, void* value) {
530 * {
531 * // We know for sure that type is either INT or FLOAT, and we want this
532 * // code to run as quickly as possible.
533 * switch (type) {
534 * case VALUE_INT:
535 * return *(int*) value;
536 * case VALUE_FLOAT:
537 * return (int) *(float*) value;
538 * default:
539 * MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE("Unexpected ValueType");
540 * }
541 * }
542 */
543
544 /*
545 * Unconditional assert in debug builds for (assumed) unreachable code paths
546 * that have a safe return without crashing in release builds.
547 */
548 #define MOZ_ASSERT_UNREACHABLE(reason) \
549 MOZ_ASSERT(false, "MOZ_ASSERT_UNREACHABLE: " reason)
550
551 #define MOZ_MAKE_COMPILER_ASSUME_IS_UNREACHABLE(reason) \
552 do { \
553 MOZ_ASSERT_UNREACHABLE(reason); \
554 MOZ_ASSUME_UNREACHABLE_MARKER(); \
555 } while (0)
556
557 /**
558 * MOZ_FALLTHROUGH_ASSERT is an annotation to suppress compiler warnings about
559 * switch cases that MOZ_ASSERT(false) (or its alias MOZ_ASSERT_UNREACHABLE) in
560 * debug builds, but intentionally fall through in release builds to handle
561 * unexpected values.
562 *
563 * Why do we need MOZ_FALLTHROUGH_ASSERT in addition to MOZ_FALLTHROUGH? In
564 * release builds, the MOZ_ASSERT(false) will expand to `do { } while (0)`,
565 * requiring a MOZ_FALLTHROUGH annotation to suppress a -Wimplicit-fallthrough
566 * warning. In debug builds, the MOZ_ASSERT(false) will expand to something like
567 * `if (true) { MOZ_CRASH(); }` and the MOZ_FALLTHROUGH annotation will cause
568 * a -Wunreachable-code warning. The MOZ_FALLTHROUGH_ASSERT macro breaks this
569 * warning stalemate.
570 *
571 * // Example before MOZ_FALLTHROUGH_ASSERT:
572 * switch (foo) {
573 * default:
574 * // This case wants to assert in debug builds, fall through in release.
575 * MOZ_ASSERT(false); // -Wimplicit-fallthrough warning in release builds!
576 * MOZ_FALLTHROUGH; // but -Wunreachable-code warning in debug builds!
577 * case 5:
578 * return 5;
579 * }
580 *
581 * // Example with MOZ_FALLTHROUGH_ASSERT:
582 * switch (foo) {
583 * default:
584 * // This case asserts in debug builds, falls through in release.
585 * MOZ_FALLTHROUGH_ASSERT("Unexpected foo value?!");
586 * case 5:
587 * return 5;
588 * }
589 */
590 #ifdef DEBUG
591 # define MOZ_FALLTHROUGH_ASSERT(reason) MOZ_CRASH("MOZ_FALLTHROUGH_ASSERT: " reason)
592 #else
593 # define MOZ_FALLTHROUGH_ASSERT(...) MOZ_FALLTHROUGH
594 #endif
595
596 /*
597 * MOZ_ALWAYS_TRUE(expr) and MOZ_ALWAYS_FALSE(expr) always evaluate the provided
598 * expression, in debug builds and in release builds both. Then, in debug
599 * builds only, the value of the expression is asserted either true or false
600 * using MOZ_ASSERT.
601 */
602 #ifdef DEBUG
603 # define MOZ_ALWAYS_TRUE(expr) \
604 do { \
605 if ((expr)) { \
606 /* Do nothing. */ \
607 } else { \
608 MOZ_ASSERT(false, #expr); \
609 } \
610 } while (0)
611 # define MOZ_ALWAYS_FALSE(expr) \
612 do { \
613 if ((expr)) { \
614 MOZ_ASSERT(false, #expr); \
615 } else { \
616 /* Do nothing. */ \
617 } \
618 } while (0)
619 #else
620 # define MOZ_ALWAYS_TRUE(expr) \
621 do { \
622 if ((expr)) { \
623 /* Silence MOZ_MUST_USE. */ \
624 } \
625 } while (0)
626 # define MOZ_ALWAYS_FALSE(expr) \
627 do { \
628 if ((expr)) { \
629 /* Silence MOZ_MUST_USE. */ \
630 } \
631 } while (0)
632 #endif
633
634 #undef MOZ_DUMP_ASSERTION_STACK
635 #undef MOZ_CRASH_CRASHREPORT
636
637 #endif /* mozilla_Assertions_h */
638