src/common/macros.h

   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 #define bt_max_t(type, a, b)    \
  11         ((type) (a) > (type) (b) ? (type) (a) : (type) (b))
  12
  13 /*
  14  * BT_HIDDEN: set the hidden attribute for internal functions
  15  * On Windows, symbols are local unless explicitly exported,
  16  * see https://gcc.gnu.org/wiki/Visibility
  17  */
  18 #if defined(_WIN32) || defined(__CYGWIN__)
  19 #define BT_HIDDEN
  20 #else
  21 #define BT_HIDDEN __attribute__((visibility("hidden")))
  22 #endif
  23
  24 /*
  25  * Yield `ref`'s value while setting `ref` to NULL.
  26  *
  27  * This can be used to give a strong reference to a callee:
  28  *
  29  *   add_foo_to_list(list, BT_MOVE_REF(foo));
  30  *
  31  * or in a simple assignment:
  32  *
  33  *   my_struct->foo = BT_MOVE_REF(foo);
  34  *
  35  * When moving a reference in a function call, the reference is given to the
  36  * callee even if that function call fails, so make sure the called function
  37  * is written accordingly.
  38  */
  39
  40 #define BT_MOVE_REF(ref)                \
  41         ({                              \
  42                 typeof(ref) _ref = ref; \
  43                 ref = NULL;             \
  44                 _ref;                   \
  45         })
  46
  47 /*
  48  * Copied from:
  49  * <https://stackoverflow.com/questions/37411809/how-to-elegantly-fix-this-unused-variable-warning/37412551#37412551>:
  50  *
  51  * * sizeof() ensures that the expression is not evaluated at all, so
  52  *   its side-effects don't happen. That is to be consistent with the
  53  *   usual behaviour of debug-only constructs, such as assert().
  54  *
  55  * * `((_expr), 0)` uses the comma operator to swallow the actual type
  56  *   of `(_expr)`. This is to prevent VLAs from triggering evaluation.
  57  *
  58  * * `(void)` explicitly ignores the result of `(_expr)` and sizeof() so
  59  *   no "unused value" warning appears.
  60  */
  61
  62 #define BT_USE_EXPR(_expr)              ((void) sizeof((void) (_expr), 0))
  63 #define BT_USE_EXPR2(_expr1, _expr2)                                    \
  64         ((void) sizeof((void) (_expr1), (void) (_expr2), 0))
  65 #define BT_USE_EXPR3(_expr1, _expr2, _expr3)                            \
  66         ((void) sizeof((void) (_expr1), (void) (_expr2), (void) (_expr3), 0))
  67 #define BT_USE_EXPR4(_expr1, _expr2, _expr3, _expr4)                    \
  68         ((void) sizeof((void) (_expr1), (void) (_expr2),                \
  69                 (void) (_expr3), (void) (_expr4), 0))
  70 #define BT_USE_EXPR5(_expr1, _expr2, _expr3, _expr4, _expr5)            \
  71         ((void) sizeof((void) (_expr1), (void) (_expr2),                \
  72                 (void) (_expr3), (void) (_expr4), (void) (_expr5), 0))
  73
  74 #endif