1 | /* Compile-time assert-like macros. |
2 | |
3 | Copyright (C) 2005-2006, 2009-2019 Free Software Foundation, Inc. |
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 |
16 | along with this program. If not, see <https://www.gnu.org/licenses/>. */ |
17 | |
18 | /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ |
19 | |
20 | #ifndef _GL_VERIFY_H |
21 | #define _GL_VERIFY_H |
22 | |
23 | |
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. |
27 | |
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. |
31 | |
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 |
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. */ |
54 | #ifndef _GL_HAVE__STATIC_ASSERT |
55 | # include <stddef.h> |
56 | # undef _Static_assert |
57 | #endif |
58 | |
59 | /* If the compiler lacks __has_builtin, define it well enough for this |
60 | source file only. */ |
61 | #ifndef __has_builtin |
62 | # define __has_builtin(x) _GL_HAS_##x |
63 | # define _GL_HAS___builtin_unreachable (4 < __GNUC__ + (5 <= __GNUC_MINOR__)) |
64 | # define _GL_HAS___builtin_trap \ |
65 | (3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__))) |
66 | # define _GL_TEMPDEF___has_builtin |
67 | #endif |
68 | |
69 | /* Each of these macros verifies that its argument R is nonzero. To |
70 | be portable, R should be an integer constant expression. Unlike |
71 | assert (R), there is no run-time overhead. |
72 | |
73 | If _Static_assert works, verify (R) uses it directly. Similarly, |
74 | _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct |
75 | that is an operand of sizeof. |
76 | |
77 | The code below uses several ideas for C++ compilers, and for C |
78 | compilers that do not support _Static_assert: |
79 | |
80 | * The first step is ((R) ? 1 : -1). Given an expression R, of |
81 | integral or boolean or floating-point type, this yields an |
82 | expression of integral type, whose value is later verified to be |
83 | constant and nonnegative. |
84 | |
85 | * Next this expression W is wrapped in a type |
86 | struct _gl_verify_type { |
87 | unsigned int _gl_verify_error_if_negative: W; |
88 | }. |
89 | If W is negative, this yields a compile-time error. No compiler can |
90 | deal with a bit-field of negative size. |
91 | |
92 | One might think that an array size check would have the same |
93 | effect, that is, that the type struct { unsigned int dummy[W]; } |
94 | would work as well. However, inside a function, some compilers |
95 | (such as C++ compilers and GNU C) allow local parameters and |
96 | variables inside array size expressions. With these compilers, |
97 | an array size check would not properly diagnose this misuse of |
98 | the verify macro: |
99 | |
100 | void function (int n) { verify (n < 0); } |
101 | |
102 | * For the verify macro, the struct _gl_verify_type will need to |
103 | somehow be embedded into a declaration. To be portable, this |
104 | declaration must declare an object, a constant, a function, or a |
105 | typedef name. If the declared entity uses the type directly, |
106 | such as in |
107 | |
108 | struct dummy {...}; |
109 | typedef struct {...} dummy; |
110 | extern struct {...} *dummy; |
111 | extern void dummy (struct {...} *); |
112 | extern struct {...} *dummy (void); |
113 | |
114 | two uses of the verify macro would yield colliding declarations |
115 | if the entity names are not disambiguated. A workaround is to |
116 | attach the current line number to the entity name: |
117 | |
118 | #define _GL_CONCAT0(x, y) x##y |
119 | #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
120 | extern struct {...} * _GL_CONCAT (dummy, __LINE__); |
121 | |
122 | But this has the problem that two invocations of verify from |
123 | within the same macro would collide, since the __LINE__ value |
124 | would be the same for both invocations. (The GCC __COUNTER__ |
125 | macro solves this problem, but is not portable.) |
126 | |
127 | A solution is to use the sizeof operator. It yields a number, |
128 | getting rid of the identity of the type. Declarations like |
129 | |
130 | extern int dummy [sizeof (struct {...})]; |
131 | extern void dummy (int [sizeof (struct {...})]); |
132 | extern int (*dummy (void)) [sizeof (struct {...})]; |
133 | |
134 | can be repeated. |
135 | |
136 | * Should the implementation use a named struct or an unnamed struct? |
137 | Which of the following alternatives can be used? |
138 | |
139 | extern int dummy [sizeof (struct {...})]; |
140 | extern int dummy [sizeof (struct _gl_verify_type {...})]; |
141 | extern void dummy (int [sizeof (struct {...})]); |
142 | extern void dummy (int [sizeof (struct _gl_verify_type {...})]); |
143 | extern int (*dummy (void)) [sizeof (struct {...})]; |
144 | extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})]; |
145 | |
146 | In the second and sixth case, the struct type is exported to the |
147 | outer scope; two such declarations therefore collide. GCC warns |
148 | about the first, third, and fourth cases. So the only remaining |
149 | possibility is the fifth case: |
150 | |
151 | extern int (*dummy (void)) [sizeof (struct {...})]; |
152 | |
153 | * GCC warns about duplicate declarations of the dummy function if |
154 | -Wredundant-decls is used. GCC 4.3 and later have a builtin |
155 | __COUNTER__ macro that can let us generate unique identifiers for |
156 | each dummy function, to suppress this warning. |
157 | |
158 | * This implementation exploits the fact that older versions of GCC, |
159 | which do not support _Static_assert, also do not warn about the |
160 | last declaration mentioned above. |
161 | |
162 | * GCC warns if -Wnested-externs is enabled and 'verify' is used |
163 | within a function body; but inside a function, you can always |
164 | arrange to use verify_expr instead. |
165 | |
166 | * In C++, any struct definition inside sizeof is invalid. |
167 | Use a template type to work around the problem. */ |
168 | |
169 | /* Concatenate two preprocessor tokens. */ |
170 | #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
171 | #define _GL_CONCAT0(x, y) x##y |
172 | |
173 | /* _GL_COUNTER is an integer, preferably one that changes each time we |
174 | use it. Use __COUNTER__ if it works, falling back on __LINE__ |
175 | otherwise. __LINE__ isn't perfect, but it's better than a |
176 | constant. */ |
177 | #if defined __COUNTER__ && __COUNTER__ != __COUNTER__ |
178 | # define _GL_COUNTER __COUNTER__ |
179 | #else |
180 | # define _GL_COUNTER __LINE__ |
181 | #endif |
182 | |
183 | /* Generate a symbol with the given prefix, making it unique if |
184 | possible. */ |
185 | #define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER) |
186 | |
187 | /* Verify requirement R at compile-time, as an integer constant expression |
188 | that returns 1. If R is false, fail at compile-time, preferably |
189 | with a diagnostic that includes the string-literal DIAGNOSTIC. */ |
190 | |
191 | #define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \ |
192 | (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC))) |
193 | |
194 | #ifdef __cplusplus |
195 | # if !GNULIB_defined_struct__gl_verify_type |
196 | template <int w> |
197 | struct _gl_verify_type { |
198 | unsigned int _gl_verify_error_if_negative: w; |
199 | }; |
200 | # define GNULIB_defined_struct__gl_verify_type 1 |
201 | # endif |
202 | # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
203 | _gl_verify_type<(R) ? 1 : -1> |
204 | #elif defined _GL_HAVE__STATIC_ASSERT |
205 | # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
206 | struct { \ |
207 | _Static_assert (R, DIAGNOSTIC); \ |
208 | int _gl_dummy; \ |
209 | } |
210 | #else |
211 | # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ |
212 | struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; } |
213 | #endif |
214 | |
215 | /* Verify requirement R at compile-time, as a declaration without a |
216 | trailing ';'. If R is false, fail at compile-time. |
217 | |
218 | This macro requires three or more arguments but uses at most the first |
219 | two, so that the _Static_assert macro optionally defined below supports |
220 | both the C11 two-argument syntax and the C2X one-argument syntax. |
221 | |
222 | Unfortunately, unlike C11, this implementation must appear as an |
223 | ordinary declaration, and cannot appear inside struct { ... }. */ |
224 | |
225 | #if defined _GL_HAVE__STATIC_ASSERT |
226 | # define _GL_VERIFY(R, DIAGNOSTIC, ...) _Static_assert (R, DIAGNOSTIC) |
227 | #else |
228 | # define _GL_VERIFY(R, DIAGNOSTIC, ...) \ |
229 | extern int (*_GL_GENSYM (_gl_verify_function) (void)) \ |
230 | [_GL_VERIFY_TRUE (R, DIAGNOSTIC)] |
231 | #endif |
232 | |
233 | /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */ |
234 | #ifdef _GL_STATIC_ASSERT_H |
235 | # if !defined _GL_HAVE__STATIC_ASSERT1 && !defined _Static_assert |
236 | # define _Static_assert(...) \ |
237 | _GL_VERIFY (__VA_ARGS__, "static assertion failed", -) |
238 | # endif |
239 | # if !defined _GL_HAVE_STATIC_ASSERT1 && !defined static_assert |
240 | # define static_assert _Static_assert /* C11 requires this #define. */ |
241 | # endif |
242 | #endif |
243 | |
244 | /* @assert.h omit start@ */ |
245 | |
246 | /* Each of these macros verifies that its argument R is nonzero. To |
247 | be portable, R should be an integer constant expression. Unlike |
248 | assert (R), there is no run-time overhead. |
249 | |
250 | There are two macros, since no single macro can be used in all |
251 | contexts in C. verify_expr (R, E) is for scalar contexts, including |
252 | integer constant expression contexts. verify (R) is for declaration |
253 | contexts, e.g., the top level. */ |
254 | |
255 | /* Verify requirement R at compile-time. Return the value of the |
256 | expression E. */ |
257 | |
258 | #define verify_expr(R, E) \ |
259 | (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E)) |
260 | |
261 | /* Verify requirement R at compile-time, as a declaration without a |
262 | trailing ';'. verify (R) acts like static_assert (R) except that |
263 | it is portable to C11/C++14 and earlier, it can issue better |
264 | diagnostics, and its name is shorter and may be more convenient. */ |
265 | |
266 | #ifdef __PGI |
267 | /* PGI barfs if R is long. */ |
268 | # define verify(R) _GL_VERIFY (R, "verify (...)", -) |
269 | #else |
270 | # define verify(R) _GL_VERIFY (R, "verify (" #R ")", -) |
271 | #endif |
272 | |
273 | /* Assume that R always holds. Behavior is undefined if R is false, |
274 | fails to evaluate, or has side effects. Although assuming R can |
275 | help a compiler generate better code or diagnostics, performance |
276 | can suffer if R uses hard-to-optimize features such as function |
277 | calls not inlined by the compiler. */ |
278 | |
279 | #if __has_builtin (__builtin_unreachable) |
280 | # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) |
281 | #elif 1200 <= _MSC_VER |
282 | # define assume(R) __assume (R) |
283 | #elif (defined GCC_LINT || defined lint) && __has_builtin (__builtin_trap) |
284 | /* Doing it this way helps various packages when configured with |
285 | --enable-gcc-warnings, which compiles with -Dlint. It's nicer |
286 | when 'assume' silences warnings even with older GCCs. */ |
287 | # define assume(R) ((R) ? (void) 0 : __builtin_trap ()) |
288 | #else |
289 | /* Some tools grok NOTREACHED, e.g., Oracle Studio 12.6. */ |
290 | # define assume(R) ((R) ? (void) 0 : /*NOTREACHED*/ (void) 0) |
291 | #endif |
292 | |
293 | #ifdef _GL_TEMPDEF___has_builtin |
294 | # undef __has_builtin |
295 | # undef _GL_HAS___builtin_unreachable |
296 | # undef _GL_HAS___builtin_trap |
297 | # undef _GL_TEMPDEF___has_builtin |
298 | #endif |
299 | |
300 | /* @assert.h omit end@ */ |
301 | |
302 | #endif |
303 | |