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8690e634 JK |
1 | /* Compile-time assert-like macros. |
2 | ||
c0c3707f | 3 | Copyright (C) 2005-2006, 2009-2019 Free Software Foundation, Inc. |
8690e634 JK |
4 | |
5 | This program is free software: you can redistribute it and/or modify | |
6 | it under the terms of the GNU General Public License as published by | |
7 | the Free Software Foundation; either version 3 of the License, or | |
8 | (at your option) any later version. | |
9 | ||
10 | This program is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | GNU General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU General Public License | |
c0c3707f | 16 | along with this program. If not, see <https://www.gnu.org/licenses/>. */ |
8690e634 JK |
17 | |
18 | /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ | |
19 | ||
20 | #ifndef _GL_VERIFY_H | |
4a626d0a | 21 | #define _GL_VERIFY_H |
8690e634 JK |
22 | |
23 | ||
c0c3707f CB |
24 | /* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert (R, DIAGNOSTIC) |
25 | works as per C11. This is supported by GCC 4.6.0 and later, in C | |
26 | mode. | |
8690e634 | 27 | |
c0c3707f CB |
28 | Define _GL_HAVE__STATIC_ASSERT1 to 1 if _Static_assert (R) works as |
29 | per C2X, and define _GL_HAVE_STATIC_ASSERT1 if static_assert (R) | |
30 | works as per C++17. This is supported by GCC 9.1 and later. | |
8690e634 | 31 | |
c0c3707f CB |
32 | Support compilers claiming conformance to the relevant standard, |
33 | and also support GCC when not pedantic. If we were willing to slow | |
34 | 'configure' down we could also use it with other compilers, but | |
35 | since this affects only the quality of diagnostics, why bother? */ | |
36 | #ifndef __cplusplus | |
37 | # if (201112L <= __STDC_VERSION__ \ | |
38 | || (!defined __STRICT_ANSI__ && 4 < __GNUC__ + (6 <= __GNUC_MINOR__))) | |
39 | # define _GL_HAVE__STATIC_ASSERT 1 | |
40 | # endif | |
41 | # if (202000L <= __STDC_VERSION__ \ | |
42 | || (!defined __STRICT_ANSI__ && 9 <= __GNUC__)) | |
43 | # define _GL_HAVE__STATIC_ASSERT1 1 | |
44 | # endif | |
45 | #else | |
46 | # if 201703L <= __cplusplus || 9 <= __GNUC__ | |
47 | # define _GL_HAVE_STATIC_ASSERT1 1 | |
48 | # endif | |
4a626d0a PA |
49 | #endif |
50 | ||
51 | /* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other | |
52 | system headers, defines a conflicting _Static_assert that is no | |
53 | better than ours; override it. */ | |
c0c3707f | 54 | #ifndef _GL_HAVE__STATIC_ASSERT |
4a626d0a PA |
55 | # include <stddef.h> |
56 | # undef _Static_assert | |
57 | #endif | |
8690e634 JK |
58 | |
59 | /* Each of these macros verifies that its argument R is nonzero. To | |
60 | be portable, R should be an integer constant expression. Unlike | |
61 | assert (R), there is no run-time overhead. | |
62 | ||
63 | If _Static_assert works, verify (R) uses it directly. Similarly, | |
64 | _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct | |
65 | that is an operand of sizeof. | |
66 | ||
67 | The code below uses several ideas for C++ compilers, and for C | |
68 | compilers that do not support _Static_assert: | |
69 | ||
70 | * The first step is ((R) ? 1 : -1). Given an expression R, of | |
71 | integral or boolean or floating-point type, this yields an | |
72 | expression of integral type, whose value is later verified to be | |
73 | constant and nonnegative. | |
74 | ||
75 | * Next this expression W is wrapped in a type | |
76 | struct _gl_verify_type { | |
77 | unsigned int _gl_verify_error_if_negative: W; | |
78 | }. | |
79 | If W is negative, this yields a compile-time error. No compiler can | |
80 | deal with a bit-field of negative size. | |
81 | ||
82 | One might think that an array size check would have the same | |
83 | effect, that is, that the type struct { unsigned int dummy[W]; } | |
84 | would work as well. However, inside a function, some compilers | |
85 | (such as C++ compilers and GNU C) allow local parameters and | |
86 | variables inside array size expressions. With these compilers, | |
87 | an array size check would not properly diagnose this misuse of | |
88 | the verify macro: | |
89 | ||
90 | void function (int n) { verify (n < 0); } | |
91 | ||
92 | * For the verify macro, the struct _gl_verify_type will need to | |
93 | somehow be embedded into a declaration. To be portable, this | |
94 | declaration must declare an object, a constant, a function, or a | |
95 | typedef name. If the declared entity uses the type directly, | |
96 | such as in | |
97 | ||
98 | struct dummy {...}; | |
99 | typedef struct {...} dummy; | |
100 | extern struct {...} *dummy; | |
101 | extern void dummy (struct {...} *); | |
102 | extern struct {...} *dummy (void); | |
103 | ||
104 | two uses of the verify macro would yield colliding declarations | |
105 | if the entity names are not disambiguated. A workaround is to | |
106 | attach the current line number to the entity name: | |
107 | ||
108 | #define _GL_CONCAT0(x, y) x##y | |
109 | #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) | |
110 | extern struct {...} * _GL_CONCAT (dummy, __LINE__); | |
111 | ||
112 | But this has the problem that two invocations of verify from | |
113 | within the same macro would collide, since the __LINE__ value | |
114 | would be the same for both invocations. (The GCC __COUNTER__ | |
115 | macro solves this problem, but is not portable.) | |
116 | ||
117 | A solution is to use the sizeof operator. It yields a number, | |
118 | getting rid of the identity of the type. Declarations like | |
119 | ||
120 | extern int dummy [sizeof (struct {...})]; | |
121 | extern void dummy (int [sizeof (struct {...})]); | |
122 | extern int (*dummy (void)) [sizeof (struct {...})]; | |
123 | ||
124 | can be repeated. | |
125 | ||
126 | * Should the implementation use a named struct or an unnamed struct? | |
127 | Which of the following alternatives can be used? | |
128 | ||
129 | extern int dummy [sizeof (struct {...})]; | |
130 | extern int dummy [sizeof (struct _gl_verify_type {...})]; | |
131 | extern void dummy (int [sizeof (struct {...})]); | |
132 | extern void dummy (int [sizeof (struct _gl_verify_type {...})]); | |
133 | extern int (*dummy (void)) [sizeof (struct {...})]; | |
134 | extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})]; | |
135 | ||
136 | In the second and sixth case, the struct type is exported to the | |
137 | outer scope; two such declarations therefore collide. GCC warns | |
138 | about the first, third, and fourth cases. So the only remaining | |
139 | possibility is the fifth case: | |
140 | ||
141 | extern int (*dummy (void)) [sizeof (struct {...})]; | |
142 | ||
143 | * GCC warns about duplicate declarations of the dummy function if | |
a512b375 | 144 | -Wredundant-decls is used. GCC 4.3 and later have a builtin |
8690e634 JK |
145 | __COUNTER__ macro that can let us generate unique identifiers for |
146 | each dummy function, to suppress this warning. | |
147 | ||
148 | * This implementation exploits the fact that older versions of GCC, | |
149 | which do not support _Static_assert, also do not warn about the | |
150 | last declaration mentioned above. | |
151 | ||
c0c3707f | 152 | * GCC warns if -Wnested-externs is enabled and 'verify' is used |
a512b375 | 153 | within a function body; but inside a function, you can always |
c0c3707f | 154 | arrange to use verify_expr instead. |
a512b375 | 155 | |
8690e634 JK |
156 | * In C++, any struct definition inside sizeof is invalid. |
157 | Use a template type to work around the problem. */ | |
158 | ||
159 | /* Concatenate two preprocessor tokens. */ | |
4a626d0a PA |
160 | #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
161 | #define _GL_CONCAT0(x, y) x##y | |
8690e634 JK |
162 | |
163 | /* _GL_COUNTER is an integer, preferably one that changes each time we | |
164 | use it. Use __COUNTER__ if it works, falling back on __LINE__ | |
165 | otherwise. __LINE__ isn't perfect, but it's better than a | |
166 | constant. */ | |
4a626d0a PA |
167 | #if defined __COUNTER__ && __COUNTER__ != __COUNTER__ |
168 | # define _GL_COUNTER __COUNTER__ | |
169 | #else | |
170 | # define _GL_COUNTER __LINE__ | |
171 | #endif | |
8690e634 JK |
172 | |
173 | /* Generate a symbol with the given prefix, making it unique if | |
174 | possible. */ | |
4a626d0a | 175 | #define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER) |
8690e634 JK |
176 | |
177 | /* Verify requirement R at compile-time, as an integer constant expression | |
178 | that returns 1. If R is false, fail at compile-time, preferably | |
179 | with a diagnostic that includes the string-literal DIAGNOSTIC. */ | |
180 | ||
4a626d0a PA |
181 | #define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \ |
182 | (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC))) | |
8690e634 | 183 | |
4a626d0a PA |
184 | #ifdef __cplusplus |
185 | # if !GNULIB_defined_struct__gl_verify_type | |
8690e634 JK |
186 | template <int w> |
187 | struct _gl_verify_type { | |
188 | unsigned int _gl_verify_error_if_negative: w; | |
189 | }; | |
4a626d0a | 190 | # define GNULIB_defined_struct__gl_verify_type 1 |
8690e634 | 191 | # endif |
4a626d0a PA |
192 | # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
193 | _gl_verify_type<(R) ? 1 : -1> | |
194 | #elif defined _GL_HAVE__STATIC_ASSERT | |
195 | # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ | |
196 | struct { \ | |
197 | _Static_assert (R, DIAGNOSTIC); \ | |
198 | int _gl_dummy; \ | |
199 | } | |
200 | #else | |
201 | # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ | |
202 | struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; } | |
203 | #endif | |
8690e634 JK |
204 | |
205 | /* Verify requirement R at compile-time, as a declaration without a | |
c0c3707f CB |
206 | trailing ';'. If R is false, fail at compile-time. |
207 | ||
208 | This macro requires three or more arguments but uses at most the first | |
209 | two, so that the _Static_assert macro optionally defined below supports | |
210 | both the C11 two-argument syntax and the C2X one-argument syntax. | |
8690e634 JK |
211 | |
212 | Unfortunately, unlike C11, this implementation must appear as an | |
213 | ordinary declaration, and cannot appear inside struct { ... }. */ | |
214 | ||
c0c3707f CB |
215 | #if defined _GL_HAVE__STATIC_ASSERT |
216 | # define _GL_VERIFY(R, DIAGNOSTIC, ...) _Static_assert (R, DIAGNOSTIC) | |
4a626d0a | 217 | #else |
c0c3707f | 218 | # define _GL_VERIFY(R, DIAGNOSTIC, ...) \ |
4a626d0a PA |
219 | extern int (*_GL_GENSYM (_gl_verify_function) (void)) \ |
220 | [_GL_VERIFY_TRUE (R, DIAGNOSTIC)] | |
221 | #endif | |
8690e634 JK |
222 | |
223 | /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */ | |
4a626d0a | 224 | #ifdef _GL_STATIC_ASSERT_H |
c0c3707f CB |
225 | # if !defined _GL_HAVE__STATIC_ASSERT1 && !defined _Static_assert |
226 | # define _Static_assert(...) \ | |
227 | _GL_VERIFY (__VA_ARGS__, "static assertion failed", -) | |
8690e634 | 228 | # endif |
c0c3707f | 229 | # if !defined _GL_HAVE_STATIC_ASSERT1 && !defined static_assert |
4a626d0a PA |
230 | # define static_assert _Static_assert /* C11 requires this #define. */ |
231 | # endif | |
232 | #endif | |
8690e634 JK |
233 | |
234 | /* @assert.h omit start@ */ | |
235 | ||
c0c3707f CB |
236 | #if 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__)) |
237 | # define _GL_HAS_BUILTIN_TRAP 1 | |
238 | #elif defined __has_builtin | |
239 | # define _GL_HAS_BUILTIN_TRAP __has_builtin (__builtin_trap) | |
240 | #else | |
241 | # define _GL_HAS_BUILTIN_TRAP 0 | |
242 | #endif | |
243 | ||
244 | #if 4 < __GNUC__ + (5 <= __GNUC_MINOR__) | |
245 | # define _GL_HAS_BUILTIN_UNREACHABLE 1 | |
246 | #elif defined __has_builtin | |
247 | # define _GL_HAS_BUILTIN_UNREACHABLE __has_builtin (__builtin_unreachable) | |
248 | #else | |
249 | # define _GL_HAS_BUILTIN_UNREACHABLE 0 | |
250 | #endif | |
251 | ||
8690e634 JK |
252 | /* Each of these macros verifies that its argument R is nonzero. To |
253 | be portable, R should be an integer constant expression. Unlike | |
254 | assert (R), there is no run-time overhead. | |
255 | ||
256 | There are two macros, since no single macro can be used in all | |
c0c3707f | 257 | contexts in C. verify_expr (R, E) is for scalar contexts, including |
8690e634 JK |
258 | integer constant expression contexts. verify (R) is for declaration |
259 | contexts, e.g., the top level. */ | |
260 | ||
8690e634 JK |
261 | /* Verify requirement R at compile-time. Return the value of the |
262 | expression E. */ | |
263 | ||
4a626d0a PA |
264 | #define verify_expr(R, E) \ |
265 | (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E)) | |
8690e634 JK |
266 | |
267 | /* Verify requirement R at compile-time, as a declaration without a | |
c0c3707f CB |
268 | trailing ';'. verify (R) acts like static_assert (R) except that |
269 | it is portable to C11/C++14 and earlier, it can issue better | |
270 | diagnostics, and its name is shorter and may be more convenient. */ | |
8690e634 | 271 | |
c0c3707f CB |
272 | #ifdef __PGI |
273 | /* PGI barfs if R is long. */ | |
274 | # define verify(R) _GL_VERIFY (R, "verify (...)", -) | |
275 | #else | |
276 | # define verify(R) _GL_VERIFY (R, "verify (" #R ")", -) | |
4a626d0a PA |
277 | #endif |
278 | ||
c0c3707f CB |
279 | /* Assume that R always holds. Behavior is undefined if R is false, |
280 | fails to evaluate, or has side effects. Although assuming R can | |
281 | help a compiler generate better code or diagnostics, performance | |
282 | can suffer if R uses hard-to-optimize features such as function | |
283 | calls not inlined by the compiler. */ | |
4a626d0a | 284 | |
c0c3707f | 285 | #if _GL_HAS_BUILTIN_UNREACHABLE |
4a626d0a PA |
286 | # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) |
287 | #elif 1200 <= _MSC_VER | |
288 | # define assume(R) __assume (R) | |
c0c3707f | 289 | #elif (defined GCC_LINT || defined lint) && _GL_HAS_BUILTIN_TRAP |
4a626d0a PA |
290 | /* Doing it this way helps various packages when configured with |
291 | --enable-gcc-warnings, which compiles with -Dlint. It's nicer | |
292 | when 'assume' silences warnings even with older GCCs. */ | |
293 | # define assume(R) ((R) ? (void) 0 : __builtin_trap ()) | |
294 | #else | |
c0c3707f CB |
295 | /* Some tools grok NOTREACHED, e.g., Oracle Studio 12.6. */ |
296 | # define assume(R) ((R) ? (void) 0 : /*NOTREACHED*/ (void) 0) | |
4a626d0a | 297 | #endif |
8690e634 JK |
298 | |
299 | /* @assert.h omit end@ */ | |
300 | ||
301 | #endif |