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 #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_EXPORT: set the visibility for exported functions.
  25  */
  26 #if defined(_WIN32) || defined(__CYGWIN__)
  27 #define BT_EXPORT
  28 #else
  29 #define BT_EXPORT __attribute__((visibility("default")))
  30 #endif
  31
  32 /*
  33  * Yield `ref`'s value while setting `ref` to NULL.
  34  *
  35  * This can be used to give a strong reference to a callee:
  36  *
  37  *   add_foo_to_list(list, BT_MOVE_REF(foo));
  38  *
  39  * or in a simple assignment:
  40  *
  41  *   my_struct->foo = BT_MOVE_REF(foo);
  42  *
  43  * When moving a reference in a function call, the reference is given to the
  44  * callee even if that function call fails, so make sure the called function
  45  * is written accordingly.
  46  */
  47
  48 #define BT_MOVE_REF(ref)                \
  49         ({                              \
  50                 __typeof__(ref) _ref = ref;     \
  51                 ref = NULL;             \
  52                 _ref;                   \
  53         })
  54
  55 /*
  56  * Copied from:
  57  * <https://stackoverflow.com/questions/37411809/how-to-elegantly-fix-this-unused-variable-warning/37412551#37412551>:
  58  *
  59  * * sizeof() ensures that the expression is not evaluated at all, so
  60  *   its side-effects don't happen. That is to be consistent with the
  61  *   usual behaviour of debug-only constructs, such as assert().
  62  *
  63  * * `((_expr), 0)` uses the comma operator to swallow the actual type
  64  *   of `(_expr)`. This is to prevent VLAs from triggering evaluation.
  65  *
  66  * * `(void)` explicitly ignores the result of `(_expr)` and sizeof() so
  67  *   no "unused value" warning appears.
  68  */
  69
  70 #define BT_USE_EXPR(_expr)              ((void) sizeof((void) (_expr), 0))
  71 #define BT_USE_EXPR2(_expr1, _expr2)                                    \
  72         ((void) sizeof((void) (_expr1), (void) (_expr2), 0))
  73 #define BT_USE_EXPR3(_expr1, _expr2, _expr3)                            \
  74         ((void) sizeof((void) (_expr1), (void) (_expr2), (void) (_expr3), 0))
  75 #define BT_USE_EXPR4(_expr1, _expr2, _expr3, _expr4)                    \
  76         ((void) sizeof((void) (_expr1), (void) (_expr2),                \
  77                 (void) (_expr3), (void) (_expr4), 0))
  78 #define BT_USE_EXPR5(_expr1, _expr2, _expr3, _expr4, _expr5)            \
  79         ((void) sizeof((void) (_expr1), (void) (_expr2),                \
  80                 (void) (_expr3), (void) (_expr4), (void) (_expr5), 0))
  81
  82 #if defined __clang__
  83 #  if __has_warning("-Wunused-but-set-variable")
  84 #    define BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE \
  85         _Pragma("GCC diagnostic ignored \"-Wunused-but-set-variable\"")
  86 #  endif
  87 #endif
  88
  89 #if !defined BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE
  90 #  define BT_DIAG_IGNORE_UNUSED_BUT_SET_VARIABLE
  91 #endif
  92
  93 #ifdef __cplusplus
  94 }
  95 #endif
  96
  97 #endif