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
16 #include <stddef.h>
17 #include <stdio.h>
18 #include <stdlib.h>
19 #ifdef WIN32
20 /*
21 * TerminateProcess and GetCurrentProcess are defined in <winbase.h>, which
22 * further depends on <windef.h>. We hardcode these few definitions manually
23 * because those headers clutter the global namespace with a significant
24 * number of undesired macros and symbols.
25 */
26 # ifdef __cplusplus
27 extern "C" {
28 # endif
29 __declspec(dllimport) int __stdcall
30 TerminateProcess(void* hProcess, unsigned int uExitCode);
31 __declspec(dllimport) void* __stdcall GetCurrentProcess(void);
32 # ifdef __cplusplus
33 }
34 # endif
35 #else
36 # include <signal.h>
37 #endif
38 #ifdef ANDROID
39 # include <android/log.h>
40 #endif
41
42 /*
43 * MOZ_STATIC_ASSERT may be used to assert a condition *at compile time* in C.
44 * In C++11, static_assert is provided by the compiler to the same effect.
45 * This can be useful when you make certain assumptions about what must hold for
46 * optimal, or even correct, behavior. For example, you might assert that the
47 * size of a struct is a multiple of the target architecture's word size:
48 *
49 * struct S { ... };
50 * // C
51 * MOZ_STATIC_ASSERT(sizeof(S) % sizeof(size_t) == 0,
52 * "S should be a multiple of word size for efficiency");
53 * // C++11
54 * static_assert(sizeof(S) % sizeof(size_t) == 0,
55 * "S should be a multiple of word size for efficiency");
56 *
57 * This macro can be used in any location where both an extern declaration and a
58 * typedef could be used.
59 */
60 #ifndef __cplusplus
61 /*
62 * Some of the definitions below create an otherwise-unused typedef. This
63 * triggers compiler warnings with some versions of gcc, so mark the typedefs
64 * as permissibly-unused to disable the warnings.
65 */
66 # if defined(__GNUC__)
67 # define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE __attribute__((unused))
68 # else
69 # define MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE /* nothing */
70 # endif
71 # define MOZ_STATIC_ASSERT_GLUE1(x, y) x##y
72 # define MOZ_STATIC_ASSERT_GLUE(x, y) MOZ_STATIC_ASSERT_GLUE1(x, y)
73 # if defined(__SUNPRO_CC)
74 /*
75 * The Sun Studio C++ compiler is buggy when declaring, inside a function,
76 * another extern'd function with an array argument whose length contains a
77 * sizeof, triggering the error message "sizeof expression not accepted as
78 * size of array parameter". This bug (6688515, not public yet) would hit
79 * defining moz_static_assert as a function, so we always define an extern
80 * array for Sun Studio.
81 *
82 * We include the line number in the symbol name in a best-effort attempt
83 * to avoid conflicts (see below).
84 */
85 # define MOZ_STATIC_ASSERT(cond, reason) \
86 extern char MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)[(cond) ? 1 : -1]
87 # elif defined(__COUNTER__)
88 /*
89 * If there was no preferred alternative, use a compiler-agnostic version.
90 *
91 * Note that the non-__COUNTER__ version has a bug in C++: it can't be used
92 * in both |extern "C"| and normal C++ in the same translation unit. (Alas
93 * |extern "C"| isn't allowed in a function.) The only affected compiler
94 * we really care about is gcc 4.2. For that compiler and others like it,
95 * we include the line number in the function name to do the best we can to
96 * avoid conflicts. These should be rare: a conflict would require use of
97 * MOZ_STATIC_ASSERT on the same line in separate files in the same
98 * translation unit, *and* the uses would have to be in code with
99 * different linkage, *and* the first observed use must be in C++-linkage
100 * code.
101 */
102 # define MOZ_STATIC_ASSERT(cond, reason) \
103 typedef int MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __COUNTER__)[(cond) ? 1 : -1] MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
104 # else
105 # define MOZ_STATIC_ASSERT(cond, reason) \
106 extern void MOZ_STATIC_ASSERT_GLUE(moz_static_assert, __LINE__)(int arg[(cond) ? 1 : -1]) MOZ_STATIC_ASSERT_UNUSED_ATTRIBUTE
107 # endif
108
109 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason) MOZ_STATIC_ASSERT(!(cond) || (expr), reason)
110 #else
111 #define MOZ_STATIC_ASSERT_IF(cond, expr, reason) static_assert(!(cond) || (expr), reason)
112 #endif
113
114 #ifdef __cplusplus
115 extern "C" {
116 #endif
117
118 /*
119 * Prints |s| as an assertion failure (using file and ln as the location of the
120 * assertion) to the standard debug-output channel.
121 *
122 * Usually you should use MOZ_ASSERT or MOZ_CRASH instead of this method. This
123 * method is primarily for internal use in this header, and only secondarily
124 * for use in implementing release-build assertions.
125 */
126 static MOZ_ALWAYS_INLINE void
MOZ_ReportAssertionFailure(const char * s,const char * file,int ln)127 MOZ_ReportAssertionFailure(const char* s, const char* file, int ln)
128 {
129 #ifdef ANDROID
130 __android_log_print(ANDROID_LOG_FATAL, "MOZ_Assert",
131 "Assertion failure: %s, at %s:%d\n", s, file, ln);
132 #else
133 fprintf(stderr, "Assertion failure: %s, at %s:%d\n", s, file, ln);
134 fflush(stderr);
135 #endif
136 }
137
138 static MOZ_ALWAYS_INLINE void
MOZ_ReportCrash(const char * s,const char * file,int ln)139 MOZ_ReportCrash(const char* s, const char* file, int ln)
140 {
141 #ifdef ANDROID
142 __android_log_print(ANDROID_LOG_FATAL, "MOZ_CRASH",
143 "Hit MOZ_CRASH(%s) at %s:%d\n", s, file, ln);
144 #else
145 fprintf(stderr, "Hit MOZ_CRASH(%s) at %s:%d\n", s, file, ln);
146 fflush(stderr);
147 #endif
148 }
149
150 /**
151 * MOZ_REALLY_CRASH is used in the implementation of MOZ_CRASH(). You should
152 * call MOZ_CRASH instead.
153 */
154 #if defined(_MSC_VER)
155 /*
156 * On MSVC use the __debugbreak compiler intrinsic, which produces an inline
157 * (not nested in a system function) breakpoint. This distinctively invokes
158 * Breakpad without requiring system library symbols on all stack-processing
159 * machines, as a nested breakpoint would require.
160 *
161 * We use TerminateProcess with the exit code aborting would generate
162 * because we don't want to invoke atexit handlers, destructors, library
163 * unload handlers, and so on when our process might be in a compromised
164 * state.
165 *
166 * We don't use abort() because it'd cause Windows to annoyingly pop up the
167 * process error dialog multiple times. See bug 345118 and bug 426163.
168 *
169 * We follow TerminateProcess() with a call to MOZ_NoReturn() so that the
170 * compiler doesn't hassle us to provide a return statement after a
171 * MOZ_REALLY_CRASH() call.
172 *
173 * (Technically these are Windows requirements, not MSVC requirements. But
174 * practically you need MSVC for debugging, and we only ship builds created
175 * by MSVC, so doing it this way reduces complexity.)
176 */
177
MOZ_NoReturn()178 __declspec(noreturn) __inline void MOZ_NoReturn() {}
179
180 # ifdef __cplusplus
181 # define MOZ_REALLY_CRASH() \
182 do { \
183 __debugbreak(); \
184 *((volatile int*) NULL) = 123; \
185 ::TerminateProcess(::GetCurrentProcess(), 3); \
186 ::MOZ_NoReturn(); \
187 } while (0)
188 # else
189 # define MOZ_REALLY_CRASH() \
190 do { \
191 __debugbreak(); \
192 *((volatile int*) NULL) = 123; \
193 TerminateProcess(GetCurrentProcess(), 3); \
194 MOZ_NoReturn(); \
195 } while (0)
196 # endif
197 #else
198 # ifdef __cplusplus
199 # define MOZ_REALLY_CRASH() \
200 do { \
201 *((volatile int*) NULL) = 123; \
202 ::abort(); \
203 } while (0)
204 # else
205 # define MOZ_REALLY_CRASH() \
206 do { \
207 *((volatile int*) NULL) = 123; \
208 abort(); \
209 } while (0)
210 # endif
211 #endif
212
213 /*
214 * MOZ_CRASH([explanation-string]) crashes the program, plain and simple, in a
215 * Breakpad-compatible way, in both debug and release builds.
216 *
217 * MOZ_CRASH is a good solution for "handling" failure cases when you're
218 * unwilling or unable to handle them more cleanly -- for OOM, for likely memory
219 * corruption, and so on. It's also a good solution if you need safe behavior
220 * in release builds as well as debug builds. But if the failure is one that
221 * should be debugged and fixed, MOZ_ASSERT is generally preferable.
222 *
223 * The optional explanation-string, if provided, must be a string literal
224 * explaining why we're crashing. This argument is intended for use with
225 * MOZ_CRASH() calls whose rationale is non-obvious; don't use it if it's
226 * obvious why we're crashing.
227 *
228 * If we're a DEBUG build and we crash at a MOZ_CRASH which provides an
229 * explanation-string, we print the string to stderr. Otherwise, we don't
230 * print anything; this is because we want MOZ_CRASH to be 100% safe in release
231 * builds, and it's hard to print to stderr safely when memory might have been
232 * corrupted.
233 */
234 #ifndef DEBUG
235 # define MOZ_CRASH(...) MOZ_REALLY_CRASH()
236 #else
237 # define MOZ_CRASH(...) \
238 do { \
239 MOZ_ReportCrash("" __VA_ARGS__, __FILE__, __LINE__); \
240 MOZ_REALLY_CRASH(); \
241 } while(0)
242 #endif
243
244 #ifdef __cplusplus
245 } /* extern "C" */
246 #endif
247
248 /*
249 * MOZ_ASSERT(expr [, explanation-string]) asserts that |expr| must be truthy in
250 * debug builds. If it is, execution continues. Otherwise, an error message
251 * including the expression and the explanation-string (if provided) is printed,
252 * an attempt is made to invoke any existing debugger, and execution halts.
253 * MOZ_ASSERT is fatal: no recovery is possible. Do not assert a condition
254 * which can correctly be falsy.
255 *
256 * The optional explanation-string, if provided, must be a string literal
257 * explaining the assertion. It is intended for use with assertions whose
258 * correctness or rationale is non-obvious, and for assertions where the "real"
259 * condition being tested is best described prosaically. Don't provide an
260 * explanation if it's not actually helpful.
261 *
262 * // No explanation needed: pointer arguments often must not be NULL.
263 * MOZ_ASSERT(arg);
264 *
265 * // An explanation can be helpful to explain exactly how we know an
266 * // assertion is valid.
267 * MOZ_ASSERT(state == WAITING_FOR_RESPONSE,
268 * "given that <thingA> and <thingB>, we must have...");
269 *
270 * // Or it might disambiguate multiple identical (save for their location)
271 * // assertions of the same expression.
272 * MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
273 * "we already set [[PrimitiveThis]] for this Boolean object");
274 * MOZ_ASSERT(getSlot(PRIMITIVE_THIS_SLOT).isUndefined(),
275 * "we already set [[PrimitiveThis]] for this String object");
276 *
277 * MOZ_ASSERT has no effect in non-debug builds. It is designed to catch bugs
278 * *only* during debugging, not "in the field".
279 */
280 #ifdef DEBUG
281 /* First the single-argument form. */
282 # define MOZ_ASSERT_HELPER1(expr) \
283 do { \
284 if (MOZ_UNLIKELY(!(expr))) { \
285 MOZ_ReportAssertionFailure(#expr, __FILE__, __LINE__); \
286 MOZ_REALLY_CRASH(); \
287 } \
288 } while (0)
289 /* Now the two-argument form. */
290 # define MOZ_ASSERT_HELPER2(expr, explain) \
291 do { \
292 if (MOZ_UNLIKELY(!(expr))) { \
293 MOZ_ReportAssertionFailure(#expr " (" explain ")", __FILE__, __LINE__); \
294 MOZ_REALLY_CRASH(); \
295 } \
296 } while (0)
297 /* And now, helper macrology up the wazoo. */
298 /*
299 * Count the number of arguments passed to MOZ_ASSERT, very carefully
300 * tiptoeing around an MSVC bug where it improperly expands __VA_ARGS__ as a
301 * single token in argument lists. See these URLs for details:
302 *
303 * http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement
304 * http://cplusplus.co.il/2010/07/17/variadic-macro-to-count-number-of-arguments/#comment-644
305 */
306 # define MOZ_COUNT_ASSERT_ARGS_IMPL2(_1, _2, count, ...) \
307 count
308 # define MOZ_COUNT_ASSERT_ARGS_IMPL(args) \
309 MOZ_COUNT_ASSERT_ARGS_IMPL2 args
310 # define MOZ_COUNT_ASSERT_ARGS(...) \
311 MOZ_COUNT_ASSERT_ARGS_IMPL((__VA_ARGS__, 2, 1, 0))
312 /* Pick the right helper macro to invoke. */
313 # define MOZ_ASSERT_CHOOSE_HELPER2(count) MOZ_ASSERT_HELPER##count
314 # define MOZ_ASSERT_CHOOSE_HELPER1(count) MOZ_ASSERT_CHOOSE_HELPER2(count)
315 # define MOZ_ASSERT_CHOOSE_HELPER(count) MOZ_ASSERT_CHOOSE_HELPER1(count)
316 /* The actual macro. */
317 # define MOZ_ASSERT_GLUE(x, y) x y
318 # define MOZ_ASSERT(...) \
319 MOZ_ASSERT_GLUE(MOZ_ASSERT_CHOOSE_HELPER(MOZ_COUNT_ASSERT_ARGS(__VA_ARGS__)), \
320 (__VA_ARGS__))
321 #else
322 # define MOZ_ASSERT(...) do { } while(0)
323 #endif /* DEBUG */
324
325 /*
326 * MOZ_ASSERT_IF(cond1, cond2) is equivalent to MOZ_ASSERT(cond2) if cond1 is
327 * true.
328 *
329 * MOZ_ASSERT_IF(isPrime(num), num == 2 || isOdd(num));
330 *
331 * As with MOZ_ASSERT, MOZ_ASSERT_IF has effect only in debug builds. It is
332 * designed to catch bugs during debugging, not "in the field".
333 */
334 #ifdef DEBUG
335 # define MOZ_ASSERT_IF(cond, expr) \
336 do { \
337 if (cond) \
338 MOZ_ASSERT(expr); \
339 } while (0)
340 #else
341 # define MOZ_ASSERT_IF(cond, expr) do { } while (0)
342 #endif
343
344 /*
345 * MOZ_ASSUME_UNREACHABLE_MARKER() expands to an expression which states that it is
346 * undefined behavior for execution to reach this point. No guarantees are made
347 * about what will happen if this is reached at runtime. Most code should
348 * probably use the higher level MOZ_ASSUME_UNREACHABLE, which uses this when
349 * appropriate.
350 */
351 #if defined(__clang__)
352 # define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
353 #elif defined(__GNUC__)
354 /*
355 * __builtin_unreachable() was implemented in gcc 4.5. If we don't have
356 * that, call a noreturn function; abort() will do nicely. Qualify the call
357 * in C++ in case there's another abort() visible in local scope.
358 */
359 # if MOZ_GCC_VERSION_AT_LEAST(4, 5, 0)
360 # define MOZ_ASSUME_UNREACHABLE_MARKER() __builtin_unreachable()
361 # else
362 # ifdef __cplusplus
363 # define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
364 # else
365 # define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
366 # endif
367 # endif
368 #elif defined(_MSC_VER)
369 # define MOZ_ASSUME_UNREACHABLE_MARKER() __assume(0)
370 #else
371 # ifdef __cplusplus
372 # define MOZ_ASSUME_UNREACHABLE_MARKER() ::abort()
373 # else
374 # define MOZ_ASSUME_UNREACHABLE_MARKER() abort()
375 # endif
376 #endif
377
378 /*
379 * MOZ_ASSUME_UNREACHABLE([reason]) tells the compiler that it can assume that
380 * the macro call cannot be reached during execution. This lets the compiler
381 * generate better-optimized code under some circumstances, at the expense of
382 * the program's behavior being undefined if control reaches the
383 * MOZ_ASSUME_UNREACHABLE.
384 *
385 * In Gecko, you probably should not use this macro outside of performance- or
386 * size-critical code, because it's unsafe. If you don't care about code size
387 * or performance, you should probably use MOZ_ASSERT or MOZ_CRASH.
388 *
389 * SpiderMonkey is a different beast, and there it's acceptable to use
390 * MOZ_ASSUME_UNREACHABLE more widely.
391 *
392 * Note that MOZ_ASSUME_UNREACHABLE is noreturn, so it's valid not to return a
393 * value following a MOZ_ASSUME_UNREACHABLE call.
394 *
395 * Example usage:
396 *
397 * enum ValueType {
398 * VALUE_STRING,
399 * VALUE_INT,
400 * VALUE_FLOAT
401 * };
402 *
403 * int ptrToInt(ValueType type, void* value) {
404 * {
405 * // We know for sure that type is either INT or FLOAT, and we want this
406 * // code to run as quickly as possible.
407 * switch (type) {
408 * case VALUE_INT:
409 * return *(int*) value;
410 * case VALUE_FLOAT:
411 * return (int) *(float*) value;
412 * default:
413 * MOZ_ASSUME_UNREACHABLE("can only handle VALUE_INT and VALUE_FLOAT");
414 * }
415 * }
416 */
417 #if defined(DEBUG)
418 # define MOZ_ASSUME_UNREACHABLE(...) \
419 do { \
420 MOZ_ASSERT(false, "MOZ_ASSUME_UNREACHABLE(" __VA_ARGS__ ")"); \
421 MOZ_ASSUME_UNREACHABLE_MARKER(); \
422 } while (0)
423 #else
424 # define MOZ_ASSUME_UNREACHABLE(reason) MOZ_ASSUME_UNREACHABLE_MARKER()
425 #endif
426
427 /*
428 * MOZ_ALWAYS_TRUE(expr) and MOZ_ALWAYS_FALSE(expr) always evaluate the provided
429 * expression, in debug builds and in release builds both. Then, in debug
430 * builds only, the value of the expression is asserted either true or false
431 * using MOZ_ASSERT.
432 */
433 #ifdef DEBUG
434 # define MOZ_ALWAYS_TRUE(expr) MOZ_ASSERT((expr))
435 # define MOZ_ALWAYS_FALSE(expr) MOZ_ASSERT(!(expr))
436 #else
437 # define MOZ_ALWAYS_TRUE(expr) ((void)(expr))
438 # define MOZ_ALWAYS_FALSE(expr) ((void)(expr))
439 #endif
440
441 #endif /* mozilla_Assertions_h */
442