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 works as per C11.
25: This is supported by GCC 4.6.0 and later, in C mode, and its use
26: here generates easier-to-read diagnostics when verify (R) fails.
27:
28: Define _GL_HAVE_STATIC_ASSERT to 1 if static_assert works as per C++11.
29: This is supported by GCC 6.1.0 and later, in C++ mode.
30:
31: Use this only with GCC. If we were willing to slow 'configure'
32: down we could also use it with other compilers, but since this
33: affects only the quality of diagnostics, why bother? */
34: #if (4 < __GNUC__ + (6 <= __GNUC_MINOR__) \
35: && (201112L <= __STDC_VERSION__ || !defined __STRICT_ANSI__) \
36: && !defined __cplusplus)
37: # define _GL_HAVE__STATIC_ASSERT 1
38: #endif
39: #if (6 <= __GNUC__) && defined __cplusplus
40: # define _GL_HAVE_STATIC_ASSERT 1
41: #endif
42:
43: /* FreeBSD 9.1 <sys/cdefs.h>, included by <stddef.h> and lots of other
44: system headers, defines a conflicting _Static_assert that is no
45: better than ours; override it. */
46: #ifndef _GL_HAVE_STATIC_ASSERT
47: # include <stddef.h>
48: # undef _Static_assert
49: #endif
50:
51: /* Each of these macros verifies that its argument R is nonzero. To
52: be portable, R should be an integer constant expression. Unlike
53: assert (R), there is no run-time overhead.
54:
55: If _Static_assert works, verify (R) uses it directly. Similarly,
56: _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct
57: that is an operand of sizeof.
58:
59: The code below uses several ideas for C++ compilers, and for C
60: compilers that do not support _Static_assert:
61:
62: * The first step is ((R) ? 1 : -1). Given an expression R, of
63: integral or boolean or floating-point type, this yields an
64: expression of integral type, whose value is later verified to be
65: constant and nonnegative.
66:
67: * Next this expression W is wrapped in a type
68: struct _gl_verify_type {
69: unsigned int _gl_verify_error_if_negative: W;
70: }.
71: If W is negative, this yields a compile-time error. No compiler can
72: deal with a bit-field of negative size.
73:
74: One might think that an array size check would have the same
75: effect, that is, that the type struct { unsigned int dummy[W]; }
76: would work as well. However, inside a function, some compilers
77: (such as C++ compilers and GNU C) allow local parameters and
78: variables inside array size expressions. With these compilers,
79: an array size check would not properly diagnose this misuse of
80: the verify macro:
81:
82: void function (int n) { verify (n < 0); }
83:
84: * For the verify macro, the struct _gl_verify_type will need to
85: somehow be embedded into a declaration. To be portable, this
86: declaration must declare an object, a constant, a function, or a
87: typedef name. If the declared entity uses the type directly,
88: such as in
89:
90: struct dummy {...};
91: typedef struct {...} dummy;
92: extern struct {...} *dummy;
93: extern void dummy (struct {...} *);
94: extern struct {...} *dummy (void);
95:
96: two uses of the verify macro would yield colliding declarations
97: if the entity names are not disambiguated. A workaround is to
98: attach the current line number to the entity name:
99:
100: #define _GL_CONCAT0(x, y) x##y
101: #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
102: extern struct {...} * _GL_CONCAT (dummy, __LINE__);
103:
104: But this has the problem that two invocations of verify from
105: within the same macro would collide, since the __LINE__ value
106: would be the same for both invocations. (The GCC __COUNTER__
107: macro solves this problem, but is not portable.)
108:
109: A solution is to use the sizeof operator. It yields a number,
110: getting rid of the identity of the type. Declarations like
111:
112: extern int dummy [sizeof (struct {...})];
113: extern void dummy (int [sizeof (struct {...})]);
114: extern int (*dummy (void)) [sizeof (struct {...})];
115:
116: can be repeated.
117:
118: * Should the implementation use a named struct or an unnamed struct?
119: Which of the following alternatives can be used?
120:
121: extern int dummy [sizeof (struct {...})];
122: extern int dummy [sizeof (struct _gl_verify_type {...})];
123: extern void dummy (int [sizeof (struct {...})]);
124: extern void dummy (int [sizeof (struct _gl_verify_type {...})]);
125: extern int (*dummy (void)) [sizeof (struct {...})];
126: extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})];
127:
128: In the second and sixth case, the struct type is exported to the
129: outer scope; two such declarations therefore collide. GCC warns
130: about the first, third, and fourth cases. So the only remaining
131: possibility is the fifth case:
132:
133: extern int (*dummy (void)) [sizeof (struct {...})];
134:
135: * GCC warns about duplicate declarations of the dummy function if
136: -Wredundant-decls is used. GCC 4.3 and later have a builtin
137: __COUNTER__ macro that can let us generate unique identifiers for
138: each dummy function, to suppress this warning.
139:
140: * This implementation exploits the fact that older versions of GCC,
141: which do not support _Static_assert, also do not warn about the
142: last declaration mentioned above.
143:
144: * GCC warns if -Wnested-externs is enabled and verify() is used
145: within a function body; but inside a function, you can always
146: arrange to use verify_expr() instead.
147:
148: * In C++, any struct definition inside sizeof is invalid.
149: Use a template type to work around the problem. */
150:
151: /* Concatenate two preprocessor tokens. */
152: #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y)
153: #define _GL_CONCAT0(x, y) x##y
154:
155: /* _GL_COUNTER is an integer, preferably one that changes each time we
156: use it. Use __COUNTER__ if it works, falling back on __LINE__
157: otherwise. __LINE__ isn't perfect, but it's better than a
158: constant. */
159: #if defined __COUNTER__ && __COUNTER__ != __COUNTER__
160: # define _GL_COUNTER __COUNTER__
161: #else
162: # define _GL_COUNTER __LINE__
163: #endif
164:
165: /* Generate a symbol with the given prefix, making it unique if
166: possible. */
167: #define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER)
168:
169: /* Verify requirement R at compile-time, as an integer constant expression
170: that returns 1. If R is false, fail at compile-time, preferably
171: with a diagnostic that includes the string-literal DIAGNOSTIC. */
172:
173: #define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \
174: (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC)))
175:
176: #ifdef __cplusplus
177: # if !GNULIB_defined_struct__gl_verify_type
178: template <int w>
179: struct _gl_verify_type {
180: unsigned int _gl_verify_error_if_negative: w;
181: };
182: # define GNULIB_defined_struct__gl_verify_type 1
183: # endif
184: # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
185: _gl_verify_type<(R) ? 1 : -1>
186: #elif defined _GL_HAVE__STATIC_ASSERT
187: # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
188: struct { \
189: _Static_assert (R, DIAGNOSTIC); \
190: int _gl_dummy; \
191: }
192: #else
193: # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \
194: struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; }
195: #endif
196:
197: /* Verify requirement R at compile-time, as a declaration without a
198: trailing ';'. If R is false, fail at compile-time, preferably
199: with a diagnostic that includes the string-literal DIAGNOSTIC.
200:
201: Unfortunately, unlike C11, this implementation must appear as an
202: ordinary declaration, and cannot appear inside struct { ... }. */
203:
204: #ifdef _GL_HAVE__STATIC_ASSERT
205: # define _GL_VERIFY _Static_assert
206: #else
207: # define _GL_VERIFY(R, DIAGNOSTIC) \
208: extern int (*_GL_GENSYM (_gl_verify_function) (void)) \
209: [_GL_VERIFY_TRUE (R, DIAGNOSTIC)]
210: #endif
211:
212: /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */
213: #ifdef _GL_STATIC_ASSERT_H
214: # if !defined _GL_HAVE__STATIC_ASSERT && !defined _Static_assert
215: # define _Static_assert(R, DIAGNOSTIC) _GL_VERIFY (R, DIAGNOSTIC)
216: # endif
217: # if !defined _GL_HAVE_STATIC_ASSERT && !defined static_assert
218: # define static_assert _Static_assert /* C11 requires this #define. */
219: # endif
220: #endif
221:
222: /* @assert.h omit start@ */
223:
224: /* Each of these macros verifies that its argument R is nonzero. To
225: be portable, R should be an integer constant expression. Unlike
226: assert (R), there is no run-time overhead.
227:
228: There are two macros, since no single macro can be used in all
229: contexts in C. verify_true (R) is for scalar contexts, including
230: integer constant expression contexts. verify (R) is for declaration
231: contexts, e.g., the top level. */
232:
233: /* Verify requirement R at compile-time, as an integer constant expression.
234: Return 1. This is equivalent to verify_expr (R, 1).
235:
236: verify_true is obsolescent; please use verify_expr instead. */
237:
238: #define verify_true(R) _GL_VERIFY_TRUE (R, "verify_true (" #R ")")
239:
240: /* Verify requirement R at compile-time. Return the value of the
241: expression E. */
242:
243: #define verify_expr(R, E) \
244: (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E))
245:
246: /* Verify requirement R at compile-time, as a declaration without a
247: trailing ';'. */
248:
249: #ifdef __GNUC__
250: # define verify(R) _GL_VERIFY (R, "verify (" #R ")")
251: #else
252: /* PGI barfs if R is long. Play it safe. */
253: # define verify(R) _GL_VERIFY (R, "verify (...)")
254: #endif
255:
256: #ifndef __has_builtin
257: # define __has_builtin(x) 0
258: #endif
259:
260: /* Assume that R always holds. This lets the compiler optimize
261: accordingly. R should not have side-effects; it may or may not be
262: evaluated. Behavior is undefined if R is false. */
263:
264: #if (__has_builtin (__builtin_unreachable) \
265: || 4 < __GNUC__ + (5 <= __GNUC_MINOR__))
266: # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ())
267: #elif 1200 <= _MSC_VER
268: # define assume(R) __assume (R)
269: #elif ((defined GCC_LINT || defined lint) \
270: && (__has_builtin (__builtin_trap) \
271: || 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__))))
272: /* Doing it this way helps various packages when configured with
273: --enable-gcc-warnings, which compiles with -Dlint. It's nicer
274: when 'assume' silences warnings even with older GCCs. */
275: # define assume(R) ((R) ? (void) 0 : __builtin_trap ())
276: #else
277: /* Some tools grok NOTREACHED, e.g., Oracle Studio 12.6. */
278: # define assume(R) ((R) ? (void) 0 : /*NOTREACHED*/ (void) 0)
279: #endif
280:
281: /* @assert.h omit end@ */
282:
283: #endif
FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>
![[BACK]](/icons/cvsweb/back.gif){kind=icon}
Return to verify.h CVS log ![[TXT]](/icons/cvsweb/text.gif){kind=icon}
![[DIR]](/icons/cvsweb/dir.gif){kind=icon}
Up to [ELWIX - Embedded LightWeight unIX -] / embedaddon / libiconv / srclib