From 7e8ae1e611bdd07b74a07bb24d8d38c1ac698853 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Tue, 14 May 2019 10:49:37 -0400 Subject: [PATCH] Silence compiler "always false comparison" warning Compiling the bitfield test with gcc -Wextra generates those warnings: ../../include/babeltrace/bitfield-internal.h:38:45: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits] #define _bt_is_signed_type(type) ((type) -1 < (type) 0) This is the intent of the macro. Disable compiler warnings around use of that macro. Signed-off-by: Mathieu Desnoyers /* C99 5.2.4.2 Numerical limits */ #include /* C99 5.2.4.2 Numerical limits */ +#include /* C99 7.16 bool type */ #include /* Non-standard BIG_ENDIAN, LITTLE_ENDIAN, BYTE_ORDER */ /* @@ -40,6 +41,26 @@ #error "bitfield.h requires the compiler representation of signed integers to be two's complement." #endif +/* + * _bt_is_signed_type() willingly generates comparison of unsigned + * expression < 0, which is always false. Silence compiler warnings. + */ +#ifdef __GNUC__ +# define _BT_DIAG_PUSH _Pragma("GCC diagnostic push") +# define _BT_DIAG_POP _Pragma("GCC diagnostic pop") + +# define _BT_DIAG_STRINGIFY_1(x) #x +# define _BT_DIAG_STRINGIFY(x) _BT_DIAG_STRINGIFY_1(x) + +# define _BT_DIAG_IGNORE(option) \ + _Pragma(_BT_DIAG_STRINGIFY(GCC diagnostic ignored option)) +# define _BT_DIAG_IGNORE_TYPE_LIMITS _BT_DIAG_IGNORE("-Wtype-limits") +#else +# define _BT_DIAG_PUSH +# define _BT_DIAG_POP +# define _BT_DIAG_IGNORE +#endif + #define _bt_is_signed_type(type) ((type) -1 < (type) 0) /* @@ -359,6 +380,7 @@ do { \ unsigned long ts = sizeof(type) * CHAR_BIT; /* type size */ \ unsigned long start_unit, end_unit, this_unit; \ unsigned long end, cshift; /* cshift is "complement shift" */ \ + bool is_signed_type; \ \ if (!__length) { \ *__vptr = 0; \ @@ -370,7 +392,11 @@ do { \ end_unit = (end + (ts - 1)) / ts; \ \ this_unit = end_unit - 1; \ - if (_bt_is_signed_type(__typeof__(__v)) \ + _BT_DIAG_PUSH \ + _BT_DIAG_IGNORE_TYPE_LIMITS \ + is_signed_type = _bt_is_signed_type(__typeof__(__v)); \ + _BT_DIAG_POP \ + if (is_signed_type \ && (__ptr[this_unit] & _bt_lshift((type) 1, (end % ts ? end % ts : ts) - 1))) \ __v = ~(__typeof__(__v)) 0; \ else \ @@ -426,6 +452,7 @@ do { \ unsigned long ts = sizeof(type) * CHAR_BIT; /* type size */ \ unsigned long start_unit, end_unit, this_unit; \ unsigned long end, cshift; /* cshift is "complement shift" */ \ + bool is_signed_type; \ \ if (!__length) { \ *__vptr = 0; \ @@ -437,7 +464,11 @@ do { \ end_unit = (end + (ts - 1)) / ts; \ \ this_unit = start_unit; \ - if (_bt_is_signed_type(__typeof__(__v)) \ + _BT_DIAG_PUSH \ + _BT_DIAG_IGNORE_TYPE_LIMITS \ + is_signed_type = _bt_is_signed_type(__typeof__(__v)); \ + _BT_DIAG_POP \ + if (is_signed_type \ && (__ptr[this_unit] & _bt_lshift((type) 1, ts - (__start % ts) - 1))) \ __v = ~(__typeof__(__v)) 0; \ else \ -- 2.34.1