[babeltrace.git] / src / common / macros.h

/*
 * SPDX-License-Identifier: MIT
 *
 * Copyright 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 */

#ifndef _BABELTRACE_INTERNAL_H
#define _BABELTRACE_INTERNAL_H

#ifdef __cplusplus
extern "C" {
#endif

#ifdef __cplusplus
#define BT_EXTERN_C extern "C"
#else
#define BT_EXTERN_C
#endif

#define bt_max_t(type, a, b)	\
	((type) (a) > (type) (b) ? (type) (a) : (type) (b))

/*
 * BT_HIDDEN: set the hidden attribute for internal functions
 * On Windows, symbols are local unless explicitly exported,
 * see https://gcc.gnu.org/wiki/Visibility
 */
#if defined(_WIN32) || defined(__CYGWIN__)
#define BT_HIDDEN
#else
#define BT_HIDDEN __attribute__((visibility("hidden")))
#endif

/*
 * Yield `ref`'s value while setting `ref` to NULL.
 *
 * This can be used to give a strong reference to a callee:
 *
 *   add_foo_to_list(list, BT_MOVE_REF(foo));
 *
 * or in a simple assignment:
 *
 *   my_struct->foo = BT_MOVE_REF(foo);
 *
 * When moving a reference in a function call, the reference is given to the
 * callee even if that function call fails, so make sure the called function
 * is written accordingly.
 */

#define BT_MOVE_REF(ref) 		\
	({				\
		__typeof__(ref) _ref = ref;	\
		ref = NULL;		\
		_ref;			\
	})

/*
 * Copied from:
 * <https://stackoverflow.com/questions/37411809/how-to-elegantly-fix-this-unused-variable-warning/37412551#37412551>:
 *
 * * sizeof() ensures that the expression is not evaluated at all, so
 *   its side-effects don't happen. That is to be consistent with the
 *   usual behaviour of debug-only constructs, such as assert().
 *
 * * `((_expr), 0)` uses the comma operator to swallow the actual type
 *   of `(_expr)`. This is to prevent VLAs from triggering evaluation.
 *
 * * `(void)` explicitly ignores the result of `(_expr)` and sizeof() so
 *   no "unused value" warning appears.
 */

#define BT_USE_EXPR(_expr)		((void) sizeof((void) (_expr), 0))
#define BT_USE_EXPR2(_expr1, _expr2)					\
	((void) sizeof((void) (_expr1), (void) (_expr2), 0))
#define BT_USE_EXPR3(_expr1, _expr2, _expr3)				\
	((void) sizeof((void) (_expr1), (void) (_expr2), (void) (_expr3), 0))
#define BT_USE_EXPR4(_expr1, _expr2, _expr3, _expr4)			\
	((void) sizeof((void) (_expr1), (void) (_expr2),		\
		(void) (_expr3), (void) (_expr4), 0))
#define BT_USE_EXPR5(_expr1, _expr2, _expr3, _expr4, _expr5)		\
	((void) sizeof((void) (_expr1), (void) (_expr2),		\
		(void) (_expr3), (void) (_expr4), (void) (_expr5), 0))

#if defined __clang__
#  if __has_warning("-Wunused-but-set-variable")
#    define BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE \
	_Pragma("GCC diagnostic ignored \"-Wunused-but-set-variable\"")
#  endif
#endif

#if !defined BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE
#  define BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE
#endif

#ifdef __cplusplus
}
#endif

#endif
Commit	Line	Data
	1	/*
	2	* SPDX-License-Identifier: MIT
	3	*
	4	* Copyright 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	5	*/
	6
	7	#ifndef _BABELTRACE_INTERNAL_H
	8	#define _BABELTRACE_INTERNAL_H
	9
	10	#ifdef __cplusplus
	11	extern "C" {
	12	#endif
	13
	14	#ifdef __cplusplus
	15	#define BT_EXTERN_C extern "C"
	16	#else
	17	#define BT_EXTERN_C
	18	#endif
	19
	20	#define bt_max_t(type, a, b) \
	21	((type) (a) > (type) (b) ? (type) (a) : (type) (b))
	22
	23	/*
	24	* BT_HIDDEN: set the hidden attribute for internal functions
	25	* On Windows, symbols are local unless explicitly exported,
	26	* see https://gcc.gnu.org/wiki/Visibility
	27	*/
	28	#if defined(_WIN32) \|\| defined(__CYGWIN__)
	29	#define BT_HIDDEN
	30	#else
	31	#define BT_HIDDEN __attribute__((visibility("hidden")))
	32	#endif
	33
	34	/*
	35	* Yield `ref`'s value while setting `ref` to NULL.
	36	*
	37	* This can be used to give a strong reference to a callee:
	38	*
	39	* add_foo_to_list(list, BT_MOVE_REF(foo));
	40	*
	41	* or in a simple assignment:
	42	*
	43	* my_struct->foo = BT_MOVE_REF(foo);
	44	*
	45	* When moving a reference in a function call, the reference is given to the
	46	* callee even if that function call fails, so make sure the called function
	47	* is written accordingly.
	48	*/
	49
	50	#define BT_MOVE_REF(ref) \
	51	({ \
	52	__typeof__(ref) _ref = ref; \
	53	ref = NULL; \
	54	_ref; \
	55	})
	56
	57	/*
	58	* Copied from:
	59	* <https://stackoverflow.com/questions/37411809/how-to-elegantly-fix-this-unused-variable-warning/37412551#37412551>:
	60	*
	61	* * sizeof() ensures that the expression is not evaluated at all, so
	62	* its side-effects don't happen. That is to be consistent with the
	63	* usual behaviour of debug-only constructs, such as assert().
	64	*
	65	* * `((_expr), 0)` uses the comma operator to swallow the actual type
	66	* of `(_expr)`. This is to prevent VLAs from triggering evaluation.
	67	*
	68	* * `(void)` explicitly ignores the result of `(_expr)` and sizeof() so
	69	* no "unused value" warning appears.
	70	*/
	71
	72	#define BT_USE_EXPR(_expr) ((void) sizeof((void) (_expr), 0))
	73	#define BT_USE_EXPR2(_expr1, _expr2) \
	74	((void) sizeof((void) (_expr1), (void) (_expr2), 0))
	75	#define BT_USE_EXPR3(_expr1, _expr2, _expr3) \
	76	((void) sizeof((void) (_expr1), (void) (_expr2), (void) (_expr3), 0))
	77	#define BT_USE_EXPR4(_expr1, _expr2, _expr3, _expr4) \
	78	((void) sizeof((void) (_expr1), (void) (_expr2), \
	79	(void) (_expr3), (void) (_expr4), 0))
	80	#define BT_USE_EXPR5(_expr1, _expr2, _expr3, _expr4, _expr5) \
	81	((void) sizeof((void) (_expr1), (void) (_expr2), \
	82	(void) (_expr3), (void) (_expr4), (void) (_expr5), 0))
	83
	84	#if defined __clang__
	85	# if __has_warning("-Wunused-but-set-variable")
	86	# define BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE \
	87	_Pragma("GCC diagnostic ignored \"-Wunused-but-set-variable\"")
	88	# endif
	89	#endif
	90
	91	#if !defined BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE
	92	# define BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE
	93	#endif
	94
	95	#ifdef __cplusplus
	96	}
	97	#endif
	98
	99	#endif