From: Bruno Haible Date: Sun, 22 Aug 2021 19:58:31 +0000 (+0200) Subject: gnulib-common.m4: Document the gnulib-internal _GL_ATTRIBUTE_* macros. X-Git-Tag: v1.0~2655 X-Git-Url: https://gitweb.git.savannah.gnu.org/gitweb/?a=commitdiff_plain;h=55974fb629d0f4a0a4bcae4a6d5d63e1e68e5804;p=gnulib.git gnulib-common.m4: Document the gnulib-internal _GL_ATTRIBUTE_* macros. * m4/gnulib-common.m4 (gl_COMMON_BODY): Add comments to the _GL_ATTRIBUTE_* macros, based on lib/attribute.h. --- diff --git a/ChangeLog b/ChangeLog index ef28c2b3d5..3d65fb8bec 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2021-08-22 Bruno Haible + + gnulib-common.m4: Document the gnulib-internal _GL_ATTRIBUTE_* macros. + * m4/gnulib-common.m4 (gl_COMMON_BODY): Add comments to the + _GL_ATTRIBUTE_* macros, based on lib/attribute.h. + 2021-08-22 Bernhard Voelker doc: fix order of stdlib functions diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4 index c801b3de94..174113b287 100644 --- a/m4/gnulib-common.m4 +++ b/m4/gnulib-common.m4 @@ -111,24 +111,39 @@ AC_DEFUN([gl_COMMON_BODY], [ ]dnl There is no _GL_ATTRIBUTE_ALIGNED; use stdalign's _Alignas instead. [ +/* _GL_ATTRIBUTE_ALLOC_SIZE ((N)) declares that the Nth argument of the function + is the size of the returned memory block. + _GL_ATTRIBUTE_ALLOC_SIZE ((M, N)) declares that the Mth argument multiplied + by the Nth argument of the function is the size of the returned memory block. + */ +/* Applies to: function, pointer to function, function types. */ #if _GL_HAS_ATTRIBUTE (alloc_size) # define _GL_ATTRIBUTE_ALLOC_SIZE(args) __attribute__ ((__alloc_size__ args)) #else # define _GL_ATTRIBUTE_ALLOC_SIZE(args) #endif +/* _GL_ATTRIBUTE_ALWAYS_INLINE tells that the compiler should always inline the + function and report an error if it cannot do so. */ +/* Applies to: function. */ #if _GL_HAS_ATTRIBUTE (always_inline) # define _GL_ATTRIBUTE_ALWAYS_INLINE __attribute__ ((__always_inline__)) #else # define _GL_ATTRIBUTE_ALWAYS_INLINE #endif +/* _GL_ATTRIBUTE_ARTIFICIAL declares that the function is not important to show + in stack traces when debugging. The compiler should omit the function from + stack traces. */ +/* Applies to: function. */ #if _GL_HAS_ATTRIBUTE (artificial) # define _GL_ATTRIBUTE_ARTIFICIAL __attribute__ ((__artificial__)) #else # define _GL_ATTRIBUTE_ARTIFICIAL #endif +/* _GL_ATTRIBUTE_COLD declares that the function is rarely executed. */ +/* Applies to: functions. */ /* Avoid __attribute__ ((cold)) on MinGW; see thread starting at . Also, Oracle Studio 12.6 requires 'cold' not '__cold__'. */ @@ -142,18 +157,25 @@ AC_DEFUN([gl_COMMON_BODY], [ # define _GL_ATTRIBUTE_COLD #endif +/* _GL_ATTRIBUTE_CONST declares that it is OK for a compiler to omit duplicate + calls to the function with the same arguments. + This attribute is safe for a function that neither depends on nor affects + observable state, and always returns exactly once - e.g., does not loop + forever, and does not call longjmp. + (This attribute is stricter than _GL_ATTRIBUTE_PURE.) */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (const) # define _GL_ATTRIBUTE_CONST __attribute__ ((__const__)) #else # define _GL_ATTRIBUTE_CONST #endif -/* _GL_ATTRIBUTE_DEALLOC (F, I) is for functions returning pointers +/* _GL_ATTRIBUTE_DEALLOC (F, I) declares that the function returns pointers that can be freed by passing them as the Ith argument to the - function F. _GL_ATTRIBUTE_DEALLOC_FREE is for functions that - return pointers that can be freed via 'free'; it can be used - only after including stdlib.h. These macros cannot be used on - inline functions. */ + function F. + _GL_ATTRIBUTE_DEALLOC_FREE declares that the function returns pointers that + can be freed via 'free'; it can be used only after including . */ +/* Applies to: functions. Cannot be used on inline functions. */ #if _GL_GNUC_PREREQ (11, 0) # define _GL_ATTRIBUTE_DEALLOC(f, i) __attribute__ ((__malloc__ (f, i))) #else @@ -161,6 +183,14 @@ AC_DEFUN([gl_COMMON_BODY], [ #endif #define _GL_ATTRIBUTE_DEALLOC_FREE _GL_ATTRIBUTE_DEALLOC (free, 1) +/* _GL_ATTRIBUTE_DEPRECATED: Declares that an entity is deprecated. + The compiler may warn if the entity is used. */ +/* Applies to: + - function, variable, + - struct, union, struct/union member, + - enumeration, enumeration item, + - typedef, + in C++ also: namespace, class, template specialization. */ #if _GL_HAS_C_ATTRIBUTE (deprecated) # define _GL_ATTRIBUTE_DEPRECATED [[__deprecated__]] #elif _GL_HAS_ATTRIBUTE (deprecated) @@ -169,6 +199,11 @@ AC_DEFUN([gl_COMMON_BODY], [ # define _GL_ATTRIBUTE_DEPRECATED #endif +/* _GL_ATTRIBUTE_ERROR(msg) requests an error if a function is called and + the function call is not optimized away. + _GL_ATTRIBUTE_WARNING(msg) requests a warning if a function is called and + the function call is not optimized away. */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (error) # define _GL_ATTRIBUTE_ERROR(msg) __attribute__ ((__error__ (msg))) # define _GL_ATTRIBUTE_WARNING(msg) __attribute__ ((__warning__ (msg))) @@ -180,13 +215,20 @@ AC_DEFUN([gl_COMMON_BODY], [ # define _GL_ATTRIBUTE_WARNING(msg) #endif +/* _GL_ATTRIBUTE_EXTERNALLY_VISIBLE declares that the entity should remain + visible to debuggers etc., even with '-fwhole-program'. */ +/* Applies to: functions, variables. */ #if _GL_HAS_ATTRIBUTE (externally_visible) # define _GL_ATTRIBUTE_EXTERNALLY_VISIBLE __attribute__ ((externally_visible)) #else # define _GL_ATTRIBUTE_EXTERNALLY_VISIBLE #endif -/* FALLTHROUGH is special, because it always expands to something. */ +/* _GL_ATTRIBUTE_FALLTHROUGH declares that it is not a programming mistake if + the control flow falls through to the immediately following 'case' or + 'default' label. The compiler should not warn in this case. */ +/* Applies to: Empty statement (;), inside a 'switch' statement. */ +/* Always expands to something. */ #if _GL_HAS_C_ATTRIBUTE (fallthrough) # define _GL_ATTRIBUTE_FALLTHROUGH [[__fallthrough__]] #elif _GL_HAS_ATTRIBUTE (fallthrough) @@ -195,24 +237,47 @@ AC_DEFUN([gl_COMMON_BODY], [ # define _GL_ATTRIBUTE_FALLTHROUGH ((void) 0) #endif +/* _GL_ATTRIBUTE_FORMAT ((ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)) + declares that the STRING-INDEXth function argument is a format string of + style ARCHETYPE, which is one of: + printf, gnu_printf + scanf, gnu_scanf, + strftime, gnu_strftime, + strfmon, + or the same thing prefixed and suffixed with '__'. + If FIRST-TO-CHECK is not 0, arguments starting at FIRST-TO_CHECK + are suitable for the format string. */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (format) # define _GL_ATTRIBUTE_FORMAT(spec) __attribute__ ((__format__ spec)) #else # define _GL_ATTRIBUTE_FORMAT(spec) #endif +/* _GL_ATTRIBUTE_LEAF declares that if the function is called from some other + compilation unit, it executes code from that unit only by return or by + exception handling. This declaration lets the compiler optimize that unit + more aggressively. */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (leaf) # define _GL_ATTRIBUTE_LEAF __attribute__ ((__leaf__)) #else # define _GL_ATTRIBUTE_LEAF #endif +/* _GL_ATTRIBUTE_MALLOC declares that the function returns a pointer to freshly + allocated memory. */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (malloc) # define _GL_ATTRIBUTE_MALLOC __attribute__ ((__malloc__)) #else # define _GL_ATTRIBUTE_MALLOC #endif +/* _GL_ATTRIBUTE_MAY_ALIAS declares that pointers to the type may point to the + same storage as pointers to other types. Thus this declaration disables + strict aliasing optimization. */ +/* Applies to: types. */ /* Oracle Studio 12.6 mishandles may_alias despite __has_attribute OK. */ #if _GL_HAS_ATTRIBUTE (may_alias) && !defined __SUNPRO_C # define _GL_ATTRIBUTE_MAY_ALIAS __attribute__ ((__may_alias__)) @@ -220,6 +285,18 @@ AC_DEFUN([gl_COMMON_BODY], [ # define _GL_ATTRIBUTE_MAY_ALIAS #endif +/* _GL_ATTRIBUTE_MAYBE_UNUSED declares that it is not a programming mistake if + the entity is not used. The compiler should not warn if the entity is not + used. */ +/* Applies to: + - function, variable, + - struct, union, struct/union member, + - enumeration, enumeration item, + - typedef, + in C++ also: class. */ +/* In C++ and C2x, this is spelled [[__maybe_unused__]]. + GCC's syntax is __attribute__ ((__unused__)). + clang supports both syntaxes. */ #if _GL_HAS_C_ATTRIBUTE (maybe_unused) # define _GL_ATTRIBUTE_MAYBE_UNUSED [[__maybe_unused__]] #else @@ -228,6 +305,10 @@ AC_DEFUN([gl_COMMON_BODY], [ /* Earlier spellings of this macro. */ #define _UNUSED_PARAMETER_ _GL_ATTRIBUTE_MAYBE_UNUSED +/* _GL_ATTRIBUTE_NODISCARD declares that the caller of the function should not + discard the return value. The compiler may warn if the caller does not use + the return value, unless the caller uses something like ignore_value. */ +/* Applies to: function, enumeration, class. */ #if _GL_HAS_C_ATTRIBUTE (nodiscard) # define _GL_ATTRIBUTE_NODISCARD [[__nodiscard__]] #elif _GL_HAS_ATTRIBUTE (warn_unused_result) @@ -236,18 +317,30 @@ AC_DEFUN([gl_COMMON_BODY], [ # define _GL_ATTRIBUTE_NODISCARD #endif +/* _GL_ATTRIBUTE_NOINLINE tells that the compiler should not inline the + function. */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (noinline) # define _GL_ATTRIBUTE_NOINLINE __attribute__ ((__noinline__)) #else # define _GL_ATTRIBUTE_NOINLINE #endif +/* _GL_ATTRIBUTE_NONNULL ((N1, N2,...)) declares that the arguments N1, N2,... + must not be NULL. + _GL_ATTRIBUTE_NONNULL () declares that all pointer arguments must not be + null. */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (nonnull) # define _GL_ATTRIBUTE_NONNULL(args) __attribute__ ((__nonnull__ args)) #else # define _GL_ATTRIBUTE_NONNULL(args) #endif +/* _GL_ATTRIBUTE_NONSTRING declares that the contents of a character array is + not meant to be NUL-terminated. */ +/* Applies to: struct/union members and variables that are arrays of element + type '[[un]signed] char'. */ #if _GL_HAS_ATTRIBUTE (nonstring) # define _GL_ATTRIBUTE_NONSTRING __attribute__ ((__nonstring__)) #else @@ -256,47 +349,75 @@ AC_DEFUN([gl_COMMON_BODY], [ /* There is no _GL_ATTRIBUTE_NORETURN; use _Noreturn instead. */ +/* _GL_ATTRIBUTE_NOTHROW declares that the function does not throw exceptions. + */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (nothrow) && !defined __cplusplus # define _GL_ATTRIBUTE_NOTHROW __attribute__ ((__nothrow__)) #else # define _GL_ATTRIBUTE_NOTHROW #endif +/* _GL_ATTRIBUTE_PACKED declares: + For struct members: The member has the smallest possible alignment. + For struct, union, class: All members have the smallest possible alignment, + minimizing the memory required. */ +/* Applies to: struct members, struct, union, + in C++ also: class. */ #if _GL_HAS_ATTRIBUTE (packed) # define _GL_ATTRIBUTE_PACKED __attribute__ ((__packed__)) #else # define _GL_ATTRIBUTE_PACKED #endif +/* _GL_ATTRIBUTE_PURE declares that It is OK for a compiler to omit duplicate + calls to the function with the same arguments if observable state is not + changed between calls. + This attribute is safe for a function that does not affect + observable state, and always returns exactly once. + (This attribute is looser than _GL_ATTRIBUTE_CONST.) */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (pure) # define _GL_ATTRIBUTE_PURE __attribute__ ((__pure__)) #else # define _GL_ATTRIBUTE_PURE #endif +/* _GL_ATTRIBUTE_RETURNS_NONNULL declares that the function's return value is + a non-NULL pointer. */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (returns_nonnull) # define _GL_ATTRIBUTE_RETURNS_NONNULL __attribute__ ((__returns_nonnull__)) #else # define _GL_ATTRIBUTE_RETURNS_NONNULL #endif +/* _GL_ATTRIBUTE_SENTINEL(pos) declares that the variadic function expects a + trailing NULL argument. + _GL_ATTRIBUTE_SENTINEL () - The last argument is NULL (requires C99). + _GL_ATTRIBUTE_SENTINEL ((N)) - The (N+1)st argument from the end is NULL. */ +/* Applies to: functions. */ #if _GL_HAS_ATTRIBUTE (sentinel) # define _GL_ATTRIBUTE_SENTINEL(pos) __attribute__ ((__sentinel__ pos)) #else # define _GL_ATTRIBUTE_SENTINEL(pos) #endif +/* A helper macro. Don't use it directly. */ #if _GL_HAS_ATTRIBUTE (unused) # define _GL_ATTRIBUTE_UNUSED __attribute__ ((__unused__)) #else # define _GL_ATTRIBUTE_UNUSED #endif -/* Earlier spellings of this macro. */ +/* Alternative spelling of this macro, for convenience. */ #define _GL_UNUSED _GL_ATTRIBUTE_UNUSED ]dnl There is no _GL_ATTRIBUTE_VISIBILITY; see m4/visibility.m4 instead. [ -/* To support C++ as well as C, use _GL_UNUSED_LABEL with trailing ';'. */ +/* _GL_UNUSED_LABEL; declares that it is not a programming mistake if the + immediately preceding label is not used. The compiler should not warn + if the label is not used. */ +/* Applies to: label (both in C and C++). */ #if !defined __cplusplus || _GL_GNUC_PREREQ (4, 5) # define _GL_UNUSED_LABEL _GL_ATTRIBUTE_UNUSED #else