| 1 | /* Compile-time assert-like macros.
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| 2 |
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| 3 | Copyright (C) 2005-2006, 2009-2012 Free Software Foundation, Inc.
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| 4 |
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| 5 | This program is free software: you can redistribute it and/or modify
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| 6 | it under the terms of the GNU General Public License as published by
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| 7 | the Free Software Foundation; either version 3 of the License, or
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| 8 | (at your option) any later version.
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| 9 |
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| 10 | This program is distributed in the hope that it will be useful,
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 13 | GNU General Public License for more details.
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| 14 |
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| 15 | You should have received a copy of the GNU General Public License
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| 16 | along with this program. If not, see <http://www.gnu.org/licenses/>. */
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| 17 |
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| 18 | /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */
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| 19 |
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| 20 | #ifndef _GL_VERIFY_H
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| 21 | # define _GL_VERIFY_H
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| 22 |
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| 23 |
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| 24 | /* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert works as per C11.
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| 25 | This is supported by GCC 4.6.0 and later, in C mode, and its use
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| 26 | here generates easier-to-read diagnostics when verify (R) fails.
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| 27 |
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| 28 | Define _GL_HAVE_STATIC_ASSERT to 1 if static_assert works as per C++11.
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| 29 | This will likely be supported by future GCC versions, in C++ mode.
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| 30 |
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| 31 | Use this only with GCC. If we were willing to slow 'configure'
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| 32 | down we could also use it with other compilers, but since this
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| 33 | affects only the quality of diagnostics, why bother? */
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| 34 | # if (4 < __GNUC__ || (__GNUC__ == 4 && 6 <= __GNUC_MINOR__)) && !defined __cplusplus
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| 35 | # define _GL_HAVE__STATIC_ASSERT 1
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| 36 | # endif
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| 37 | /* The condition (99 < __GNUC__) is temporary, until we know about the
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| 38 | first G++ release that supports static_assert. */
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| 39 | # if (99 < __GNUC__) && defined __cplusplus
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| 40 | # define _GL_HAVE_STATIC_ASSERT 1
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| 41 | # endif
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| 42 |
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| 43 | /* Each of these macros verifies that its argument R is nonzero. To
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| 44 | be portable, R should be an integer constant expression. Unlike
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| 45 | assert (R), there is no run-time overhead.
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| 46 |
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| 47 | If _Static_assert works, verify (R) uses it directly. Similarly,
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| 48 | _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct
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| 49 | that is an operand of sizeof.
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| 50 |
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| 51 | The code below uses several ideas for C++ compilers, and for C
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| 52 | compilers that do not support _Static_assert:
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| 53 |
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| 54 | * The first step is ((R) ? 1 : -1). Given an expression R, of
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| 55 | integral or boolean or floating-point type, this yields an
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| 56 | expression of integral type, whose value is later verified to be
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| 57 | constant and nonnegative.
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| 58 |
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| 59 | * Next this expression W is wrapped in a type
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| 60 | struct _gl_verify_type {
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| 61 | unsigned int _gl_verify_error_if_negative: W;
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| 62 | }.
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| 63 | If W is negative, this yields a compile-time error. No compiler can
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| 64 | deal with a bit-field of negative size.
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| 65 |
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| 66 | One might think that an array size check would have the same
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| 67 | effect, that is, that the type struct { unsigned int dummy[W]; }
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| 68 | would work as well. However, inside a function, some compilers
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| 69 | (such as C++ compilers and GNU C) allow local parameters and
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| 70 | variables inside array size expressions. With these compilers,
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| 71 | an array size check would not properly diagnose this misuse of
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| 72 | the verify macro:
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| 73 |
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| 74 | void function (int n) { verify (n < 0); }
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| 75 |
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| 76 | * For the verify macro, the struct _gl_verify_type will need to
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| 77 | somehow be embedded into a declaration. To be portable, this
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| 78 | declaration must declare an object, a constant, a function, or a
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| 79 | typedef name. If the declared entity uses the type directly,
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| 80 | such as in
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| 81 |
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| 82 | struct dummy {...};
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| 83 | typedef struct {...} dummy;
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| 84 | extern struct {...} *dummy;
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| 85 | extern void dummy (struct {...} *);
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| 86 | extern struct {...} *dummy (void);
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| 87 |
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| 88 | two uses of the verify macro would yield colliding declarations
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| 89 | if the entity names are not disambiguated. A workaround is to
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| 90 | attach the current line number to the entity name:
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| 91 |
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| 92 | #define _GL_CONCAT0(x, y) x##y
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| 93 | #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
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| 94 | extern struct {...} * _GL_CONCAT (dummy, __LINE__);
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| 95 |
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| 96 | But this has the problem that two invocations of verify from
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| 97 | within the same macro would collide, since the __LINE__ value
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| 98 | would be the same for both invocations. (The GCC __COUNTER__
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| 99 | macro solves this problem, but is not portable.)
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| 100 |
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| 101 | A solution is to use the sizeof operator. It yields a number,
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| 102 | getting rid of the identity of the type. Declarations like
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| 103 |
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| 104 | extern int dummy [sizeof (struct {...})];
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| 105 | extern void dummy (int [sizeof (struct {...})]);
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| 106 | extern int (*dummy (void)) [sizeof (struct {...})];
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| 107 |
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| 108 | can be repeated.
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| 109 |
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| 110 | * Should the implementation use a named struct or an unnamed struct?
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| 111 | Which of the following alternatives can be used?
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| 112 |
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| 113 | extern int dummy [sizeof (struct {...})];
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| 114 | extern int dummy [sizeof (struct _gl_verify_type {...})];
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| 115 | extern void dummy (int [sizeof (struct {...})]);
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| 116 | extern void dummy (int [sizeof (struct _gl_verify_type {...})]);
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| 117 | extern int (*dummy (void)) [sizeof (struct {...})];
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| 118 | extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})];
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| 119 |
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| 120 | In the second and sixth case, the struct type is exported to the
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| 121 | outer scope; two such declarations therefore collide. GCC warns
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| 122 | about the first, third, and fourth cases. So the only remaining
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| 123 | possibility is the fifth case:
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| 124 |
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| 125 | extern int (*dummy (void)) [sizeof (struct {...})];
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| 126 |
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| 127 | * GCC warns about duplicate declarations of the dummy function if
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| 128 | -Wredundant_decls is used. GCC 4.3 and later have a builtin
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| 129 | __COUNTER__ macro that can let us generate unique identifiers for
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| 130 | each dummy function, to suppress this warning.
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| 131 |
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| 132 | * This implementation exploits the fact that older versions of GCC,
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| 133 | which do not support _Static_assert, also do not warn about the
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| 134 | last declaration mentioned above.
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| 135 |
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| 136 | * In C++, any struct definition inside sizeof is invalid.
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| 137 | Use a template type to work around the problem. */
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| 138 |
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| 139 | /* Concatenate two preprocessor tokens. */
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| 140 | # define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
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| 141 | # define _GL_CONCAT0(x, y) x##y
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| 142 |
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| 143 | /* _GL_COUNTER is an integer, preferably one that changes each time we
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| 144 | use it. Use __COUNTER__ if it works, falling back on __LINE__
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| 145 | otherwise. __LINE__ isn't perfect, but it's better than a
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| 146 | constant. */
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| 147 | # if defined __COUNTER__ && __COUNTER__ != __COUNTER__
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| 148 | # define _GL_COUNTER __COUNTER__
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| 149 | # else
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| 150 | # define _GL_COUNTER __LINE__
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| 151 | # endif
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| 152 |
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| 153 | /* Generate a symbol with the given prefix, making it unique if
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| 154 | possible. */
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| 155 | # define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER)
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| 156 |
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| 157 | /* Verify requirement R at compile-time, as an integer constant expression
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| 158 | that returns 1. If R is false, fail at compile-time, preferably
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| 159 | with a diagnostic that includes the string-literal DIAGNOSTIC. */
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| 160 |
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| 161 | # define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \
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| 162 | (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC)))
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| 163 |
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| 164 | # ifdef __cplusplus
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| 165 | # if !GNULIB_defined_struct__gl_verify_type
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| 166 | template <int w>
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| 167 | struct _gl_verify_type {
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| 168 | unsigned int _gl_verify_error_if_negative: w;
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| 169 | };
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| 170 | # define GNULIB_defined_struct__gl_verify_type 1
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| 171 | # endif
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| 172 | # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
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| 173 | _gl_verify_type<(R) ? 1 : -1>
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| 174 | # elif defined _GL_HAVE__STATIC_ASSERT
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| 175 | # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
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| 176 | struct { \
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| 177 | _Static_assert (R, DIAGNOSTIC); \
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| 178 | int _gl_dummy; \
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| 179 | }
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| 180 | # else
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| 181 | # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
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| 182 | struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; }
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| 183 | # endif
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| 184 |
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| 185 | /* Verify requirement R at compile-time, as a declaration without a
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| 186 | trailing ';'. If R is false, fail at compile-time, preferably
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| 187 | with a diagnostic that includes the string-literal DIAGNOSTIC.
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| 188 |
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| 189 | Unfortunately, unlike C11, this implementation must appear as an
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| 190 | ordinary declaration, and cannot appear inside struct { ... }. */
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| 191 |
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| 192 | # ifdef _GL_HAVE__STATIC_ASSERT
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| 193 | # define _GL_VERIFY _Static_assert
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| 194 | # else
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| 195 | # define _GL_VERIFY(R, DIAGNOSTIC) \
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| 196 | extern int (*_GL_GENSYM (_gl_verify_function) (void)) \
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| 197 | [_GL_VERIFY_TRUE (R, DIAGNOSTIC)]
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| 198 | # endif
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| 199 |
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| 200 | /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */
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| 201 | # ifdef _GL_STATIC_ASSERT_H
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| 202 | # if !defined _GL_HAVE__STATIC_ASSERT && !defined _Static_assert
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| 203 | # define _Static_assert(R, DIAGNOSTIC) _GL_VERIFY (R, DIAGNOSTIC)
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| 204 | # endif
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| 205 | # if !defined _GL_HAVE_STATIC_ASSERT && !defined static_assert
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| 206 | # define static_assert _Static_assert /* C11 requires this #define. */
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| 207 | # endif
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| 208 | # endif
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| 209 |
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| 210 | /* @assert.h omit start@ */
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| 211 |
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| 212 | /* Each of these macros verifies that its argument R is nonzero. To
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| 213 | be portable, R should be an integer constant expression. Unlike
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| 214 | assert (R), there is no run-time overhead.
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| 215 |
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| 216 | There are two macros, since no single macro can be used in all
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| 217 | contexts in C. verify_true (R) is for scalar contexts, including
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| 218 | integer constant expression contexts. verify (R) is for declaration
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| 219 | contexts, e.g., the top level. */
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| 220 |
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| 221 | /* Verify requirement R at compile-time, as an integer constant expression.
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| 222 | Return 1. This is equivalent to verify_expr (R, 1).
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| 223 |
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| 224 | verify_true is obsolescent; please use verify_expr instead. */
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| 225 |
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| 226 | # define verify_true(R) _GL_VERIFY_TRUE (R, "verify_true (" #R ")")
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| 227 |
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| 228 | /* Verify requirement R at compile-time. Return the value of the
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| 229 | expression E. */
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| 230 |
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| 231 | # define verify_expr(R, E) \
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| 232 | (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E))
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| 233 |
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| 234 | /* Verify requirement R at compile-time, as a declaration without a
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| 235 | trailing ';'. */
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| 236 |
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| 237 | # define verify(R) _GL_VERIFY (R, "verify (" #R ")")
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| 238 |
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| 239 | /* @assert.h omit end@ */
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| 240 |
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| 241 | #endif
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