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_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