/* Compile-time assert-like macros. Copyright (C) 2005-2006, 2009-2023 Free Software Foundation, Inc. This file is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This file is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this program. If not, see . */ /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ #ifndef _GL_VERIFY_H #define _GL_VERIFY_H /* Define _GL_HAVE__STATIC_ASSERT to 1 if _Static_assert (R, DIAGNOSTIC) works as per C11. This is supported by GCC 4.6.0+ and by clang 4+. Define _GL_HAVE__STATIC_ASSERT1 to 1 if _Static_assert (R) works as per C23. This is supported by GCC 9.1+. Support compilers claiming conformance to the relevant standard, and also support GCC when not pedantic. If we were willing to slow 'configure' down we could also use it with other compilers, but since this affects only the quality of diagnostics, why bother? */ #ifndef __cplusplus # if (201112 <= __STDC_VERSION__ \ || (!defined __STRICT_ANSI__ \ && (4 < __GNUC__ + (6 <= __GNUC_MINOR__) || 5 <= __clang_major__))) # define _GL_HAVE__STATIC_ASSERT 1 # endif # if (202311 <= __STDC_VERSION__ \ || (!defined __STRICT_ANSI__ && 9 <= __GNUC__)) # define _GL_HAVE__STATIC_ASSERT1 1 # endif #endif /* FreeBSD 9.1 , included by and lots of other system headers, defines a conflicting _Static_assert that is no better than ours; override it. */ #ifndef _GL_HAVE__STATIC_ASSERT # include # undef _Static_assert #endif /* Each of these macros verifies that its argument R is nonzero. To be portable, R should be an integer constant expression. Unlike assert (R), there is no run-time overhead. If _Static_assert works, verify (R) uses it directly. Similarly, _GL_VERIFY_TRUE works by packaging a _Static_assert inside a struct that is an operand of sizeof. The code below uses several ideas for C++ compilers, and for C compilers that do not support _Static_assert: * The first step is ((R) ? 1 : -1). Given an expression R, of integral or boolean or floating-point type, this yields an expression of integral type, whose value is later verified to be constant and nonnegative. * Next this expression W is wrapped in a type struct _gl_verify_type { unsigned int _gl_verify_error_if_negative: W; }. If W is negative, this yields a compile-time error. No compiler can deal with a bit-field of negative size. One might think that an array size check would have the same effect, that is, that the type struct { unsigned int dummy[W]; } would work as well. However, inside a function, some compilers (such as C++ compilers and GNU C) allow local parameters and variables inside array size expressions. With these compilers, an array size check would not properly diagnose this misuse of the verify macro: void function (int n) { verify (n < 0); } * For the verify macro, the struct _gl_verify_type will need to somehow be embedded into a declaration. To be portable, this declaration must declare an object, a constant, a function, or a typedef name. If the declared entity uses the type directly, such as in struct dummy {...}; typedef struct {...} dummy; extern struct {...} *dummy; extern void dummy (struct {...} *); extern struct {...} *dummy (void); two uses of the verify macro would yield colliding declarations if the entity names are not disambiguated. A workaround is to attach the current line number to the entity name: #define _GL_CONCAT0(x, y) x##y #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) extern struct {...} * _GL_CONCAT (dummy, __LINE__); But this has the problem that two invocations of verify from within the same macro would collide, since the __LINE__ value would be the same for both invocations. (The GCC __COUNTER__ macro solves this problem, but is not portable.) A solution is to use the sizeof operator. It yields a number, getting rid of the identity of the type. Declarations like extern int dummy [sizeof (struct {...})]; extern void dummy (int [sizeof (struct {...})]); extern int (*dummy (void)) [sizeof (struct {...})]; can be repeated. * Should the implementation use a named struct or an unnamed struct? Which of the following alternatives can be used? extern int dummy [sizeof (struct {...})]; extern int dummy [sizeof (struct _gl_verify_type {...})]; extern void dummy (int [sizeof (struct {...})]); extern void dummy (int [sizeof (struct _gl_verify_type {...})]); extern int (*dummy (void)) [sizeof (struct {...})]; extern int (*dummy (void)) [sizeof (struct _gl_verify_type {...})]; In the second and sixth case, the struct type is exported to the outer scope; two such declarations therefore collide. GCC warns about the first, third, and fourth cases. So the only remaining possibility is the fifth case: extern int (*dummy (void)) [sizeof (struct {...})]; * GCC warns about duplicate declarations of the dummy function if -Wredundant-decls is used. GCC 4.3 and later have a builtin __COUNTER__ macro that can let us generate unique identifiers for each dummy function, to suppress this warning. * This implementation exploits the fact that older versions of GCC, which do not support _Static_assert, also do not warn about the last declaration mentioned above. * GCC warns if -Wnested-externs is enabled and 'verify' is used within a function body; but inside a function, you can always arrange to use verify_expr instead. * In C++, any struct definition inside sizeof is invalid. Use a template type to work around the problem. */ /* Concatenate two preprocessor tokens. */ #define _GL_CONCAT(x, y) _GL_CONCAT0 (x, y) #define _GL_CONCAT0(x, y) x##y /* _GL_COUNTER is an integer, preferably one that changes each time we use it. Use __COUNTER__ if it works, falling back on __LINE__ otherwise. __LINE__ isn't perfect, but it's better than a constant. */ #if defined __COUNTER__ && __COUNTER__ != __COUNTER__ # define _GL_COUNTER __COUNTER__ #else # define _GL_COUNTER __LINE__ #endif /* Generate a symbol with the given prefix, making it unique if possible. */ #define _GL_GENSYM(prefix) _GL_CONCAT (prefix, _GL_COUNTER) /* Verify requirement R at compile-time, as an integer constant expression that returns 1. If R is false, fail at compile-time, preferably with a diagnostic that includes the string-literal DIAGNOSTIC. */ #define _GL_VERIFY_TRUE(R, DIAGNOSTIC) \ (!!sizeof (_GL_VERIFY_TYPE (R, DIAGNOSTIC))) #ifdef __cplusplus # if !GNULIB_defined_struct__gl_verify_type template struct _gl_verify_type { unsigned int _gl_verify_error_if_negative: w; }; # define GNULIB_defined_struct__gl_verify_type 1 # endif # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ _gl_verify_type<(R) ? 1 : -1> #elif defined _GL_HAVE__STATIC_ASSERT # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ struct { \ _Static_assert (R, DIAGNOSTIC); \ int _gl_dummy; \ } #else # define _GL_VERIFY_TYPE(R, DIAGNOSTIC) \ struct { unsigned int _gl_verify_error_if_negative: (R) ? 1 : -1; } #endif /* Verify requirement R at compile-time, as a declaration without a trailing ';'. If R is false, fail at compile-time. This macro requires three or more arguments but uses at most the first two, so that the _Static_assert macro optionally defined below supports both the C11 two-argument syntax and the C23 one-argument syntax. Unfortunately, unlike C11, this implementation must appear as an ordinary declaration, and cannot appear inside struct { ... }. */ #if 202311 <= __STDC_VERSION__ || 200410 <= __cpp_static_assert # define _GL_VERIFY(R, DIAGNOSTIC, ...) static_assert (R, DIAGNOSTIC) #elif defined _GL_HAVE__STATIC_ASSERT # define _GL_VERIFY(R, DIAGNOSTIC, ...) _Static_assert (R, DIAGNOSTIC) #else # define _GL_VERIFY(R, DIAGNOSTIC, ...) \ extern int (*_GL_GENSYM (_gl_verify_function) (void)) \ [_GL_VERIFY_TRUE (R, DIAGNOSTIC)] # if 4 < __GNUC__ + (6 <= __GNUC_MINOR__) # pragma GCC diagnostic ignored "-Wnested-externs" # endif #endif /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h. */ #ifdef _GL_STATIC_ASSERT_H /* Define _Static_assert if needed. */ /* With clang ≥ 3.8.0 in C++ mode, _Static_assert already works and accepts 1 or 2 arguments. We better don't override it, because clang's standard C++ library uses static_assert inside classes in several places, and our replacement via _GL_VERIFY does not work in these contexts. */ # if (defined __cplusplus && defined __clang__ \ && (4 <= __clang_major__ + (8 <= __clang_minor__))) # if 5 <= __clang_major__ /* Avoid "warning: 'static_assert' with no message is a C++17 extension". */ # pragma clang diagnostic ignored "-Wc++17-extensions" # else /* Avoid "warning: static_assert with no message is a C++1z extension". */ # pragma clang diagnostic ignored "-Wc++1z-extensions" # endif # elif !defined _GL_HAVE__STATIC_ASSERT1 && !defined _Static_assert # if !defined _MSC_VER || defined __clang__ # define _Static_assert(...) \ _GL_VERIFY (__VA_ARGS__, "static assertion failed", -) # else /* Work around MSVC preprocessor incompatibility with ISO C; see . */ # define _Static_assert(R, ...) \ _GL_VERIFY ((R), "static assertion failed", -) # endif # endif /* Define static_assert if needed. */ # if (!defined static_assert \ && __STDC_VERSION__ < 202311 \ && (!defined __cplusplus \ || (__cpp_static_assert < 201411 \ && __GNUG__ < 6 && __clang_major__ < 6))) # if defined __cplusplus && _MSC_VER >= 1900 && !defined __clang__ /* MSVC 14 in C++ mode supports the two-arguments static_assert but not the one-argument static_assert, and it does not support _Static_assert. We have to play preprocessor tricks to distinguish the two cases. Since the MSVC preprocessor is not ISO C compliant (see above),. the solution is specific to MSVC. */ # define _GL_EXPAND(x) x # define _GL_SA1(a1) static_assert ((a1), "static assertion failed") # define _GL_SA2 static_assert # define _GL_SA3 static_assert # define _GL_SA_PICK(x1,x2,x3,x4,...) x4 # define static_assert(...) _GL_EXPAND(_GL_SA_PICK(__VA_ARGS__,_GL_SA3,_GL_SA2,_GL_SA1)) (__VA_ARGS__) /* Avoid "fatal error C1189: #error: The C++ Standard Library forbids macroizing keywords." */ # define _ALLOW_KEYWORD_MACROS 1 # else # define static_assert _Static_assert /* C11 requires this #define. */ # endif # endif #endif /* @assert.h omit start@ */ #if defined __clang_major__ && __clang_major__ < 5 # define _GL_HAS_BUILTIN_TRAP 0 #elif 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__)) # define _GL_HAS_BUILTIN_TRAP 1 #elif defined __has_builtin # define _GL_HAS_BUILTIN_TRAP __has_builtin (__builtin_trap) #else # define _GL_HAS_BUILTIN_TRAP 0 #endif #ifndef _GL_HAS_BUILTIN_UNREACHABLE # if defined __clang_major__ && __clang_major__ < 5 # define _GL_HAS_BUILTIN_UNREACHABLE 0 # elif 4 < __GNUC__ + (5 <= __GNUC_MINOR__) # define _GL_HAS_BUILTIN_UNREACHABLE 1 # elif defined __has_builtin # define _GL_HAS_BUILTIN_UNREACHABLE __has_builtin (__builtin_unreachable) # else # define _GL_HAS_BUILTIN_UNREACHABLE 0 # endif #endif /* Each of these macros verifies that its argument R is nonzero. To be portable, R should be an integer constant expression. Unlike assert (R), there is no run-time overhead. There are two macros, since no single macro can be used in all contexts in C. verify_expr (R, E) is for scalar contexts, including integer constant expression contexts. verify (R) is for declaration contexts, e.g., the top level. */ /* Verify requirement R at compile-time. Return the value of the expression E. */ #define verify_expr(R, E) \ (_GL_VERIFY_TRUE (R, "verify_expr (" #R ", " #E ")") ? (E) : (E)) /* Verify requirement R at compile-time, as a declaration without a trailing ';'. verify (R) acts like static_assert (R) except that it is portable to C11/C++14 and earlier, it can issue better diagnostics, and its name is shorter and may be more convenient. */ #ifdef __PGI /* PGI barfs if R is long. */ # define verify(R) _GL_VERIFY (R, "verify (...)", -) #else # define verify(R) _GL_VERIFY (R, "verify (" #R ")", -) #endif /* Assume that R always holds. Behavior is undefined if R is false, fails to evaluate, or has side effects. 'assume (R)' is a directive from the programmer telling the compiler that R is true so the compiler needn't generate code to test R. This is why 'assume' is in verify.h: it's related to static checking (in this case, static checking done by the programmer), not dynamic checking. 'assume (R)' can affect compilation of all the code, not just code that happens to be executed after the assume (R) is "executed". For example, if the code mistakenly does 'assert (R); assume (R);' the compiler is entitled to optimize away the 'assert (R)'. Although assuming R can help a compiler generate better code or diagnostics, performance can suffer if R uses hard-to-optimize features such as function calls not inlined by the compiler. Avoid Clang's __builtin_assume, as it breaks GNU Emacs master as of 2020-08-23T21:09:49Z!eggert@cs.ucla.edu; see . It's not known whether this breakage is a Clang bug or an Emacs bug; play it safe for now. */ #if _GL_HAS_BUILTIN_UNREACHABLE # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) #elif 1200 <= _MSC_VER # define assume(R) __assume (R) #elif 202311 <= __STDC_VERSION__ # include # define assume(R) ((R) ? (void) 0 : unreachable ()) #elif (defined GCC_LINT || defined lint) && _GL_HAS_BUILTIN_TRAP /* Doing it this way helps various packages when configured with --enable-gcc-warnings, which compiles with -Dlint. It's nicer if 'assume' silences warnings with GCC 3.4 through GCC 4.4.7 (2012). */ # define assume(R) ((R) ? (void) 0 : __builtin_trap ()) #else /* Some older tools grok NOTREACHED, e.g., Oracle Studio 12.6 (2017). */ # define assume(R) ((R) ? (void) 0 : /*NOTREACHED*/ (void) 0) #endif /* @assert.h omit end@ */ #endif