| 1 | /* Compile-time assert-like macros. |
| 2 | |
| 3 | Copyright (C) 2005-2006, 2009-2020 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 | /* 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 |
| 144 | -Wredundant-decls is used. GCC 4.3 and later have a builtin |
| 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 | |
| 152 | * GCC warns if -Wnested-externs is enabled and 'verify' is used |
| 153 | within a function body; but inside a function, you can always |
| 154 | arrange to use verify_expr instead. |
| 155 | |
| 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. */ |
| 160 | #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) |
| 161 | #define _GL_CONCAT0(x, y) x##y |
| 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. */ |
| 167 | #if defined __COUNTER__ && __COUNTER__ != __COUNTER__ |
| 168 | # define _GL_COUNTER __COUNTER__ |
| 169 | #else |
| 170 | # define _GL_COUNTER __LINE__ |
| 171 | #endif |
| 172 | |
| 173 | /* Generate a symbol with the given prefix, making it unique if |
| 174 | possible. */ |
| 175 | #define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER) |
| 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 | |
| 181 | #define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \ |
| 182 | (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC))) |
| 183 | |
| 184 | #ifdef __cplusplus |
| 185 | # if !GNULIB_defined_struct__gl_verify_type |
| 186 | template <int w> |
| 187 | struct _gl_verify_type { |
| 188 | unsigned int _gl_verify_error_if_negative: w; |
| 189 | }; |
| 190 | # define GNULIB_defined_struct__gl_verify_type 1 |
| 191 | # endif |
| 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 |
| 204 | |
| 205 | /* Verify requirement R at compile-time, as a declaration without a |
| 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. |
| 211 | |
| 212 | Unfortunately, unlike C11, this implementation must appear as an |
| 213 | ordinary declaration, and cannot appear inside struct { ... }. */ |
| 214 | |
| 215 | #if defined _GL_HAVE__STATIC_ASSERT |
| 216 | # define _GL_VERIFY(R, DIAGNOSTIC, ...) _Static_assert (R, DIAGNOSTIC) |
| 217 | #else |
| 218 | # define _GL_VERIFY(R, DIAGNOSTIC, ...) \ |
| 219 | extern int (*_GL_GENSYM (_gl_verify_function) (void)) \ |
| 220 | [_GL_VERIFY_TRUE (R, DIAGNOSTIC)] |
| 221 | #endif |
| 222 | |
| 223 | /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */ |
| 224 | #ifdef _GL_STATIC_ASSERT_H |
| 225 | # if !defined _GL_HAVE__STATIC_ASSERT1 && !defined _Static_assert |
| 226 | # define _Static_assert(...) \ |
| 227 | _GL_VERIFY (__VA_ARGS__, "static assertion failed", -) |
| 228 | # endif |
| 229 | # if !defined _GL_HAVE_STATIC_ASSERT1 && !defined static_assert |
| 230 | # define static_assert _Static_assert /* C11 requires this #define. */ |
| 231 | # endif |
| 232 | #endif |
| 233 | |
| 234 | /* @assert.h omit start@ */ |
| 235 | |
| 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 | |
| 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 |
| 257 | contexts in C. verify_expr (R, E) is for scalar contexts, including |
| 258 | integer constant expression contexts. verify (R) is for declaration |
| 259 | contexts, e.g., the top level. */ |
| 260 | |
| 261 | /* Verify requirement R at compile-time. Return the value of the |
| 262 | expression E. */ |
| 263 | |
| 264 | #define verify_expr(R, E) \ |
| 265 | (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E)) |
| 266 | |
| 267 | /* Verify requirement R at compile-time, as a declaration without a |
| 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. */ |
| 271 | |
| 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 ")", -) |
| 277 | #endif |
| 278 | |
| 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. */ |
| 284 | |
| 285 | #if _GL_HAS_BUILTIN_UNREACHABLE |
| 286 | # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) |
| 287 | #elif 1200 <= _MSC_VER |
| 288 | # define assume(R) __assume (R) |
| 289 | #elif (defined GCC_LINT || defined lint) && _GL_HAS_BUILTIN_TRAP |
| 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 |
| 295 | /* Some tools grok NOTREACHED, e.g., Oracle Studio 12.6. */ |
| 296 | # define assume(R) ((R) ? (void) 0 : /*NOTREACHED*/ (void) 0) |
| 297 | #endif |
| 298 | |
| 299 | /* @assert.h omit end@ */ |
| 300 | |
| 301 | #endif |