Messages in this thread Patch in this message | | | From | Joe Stringer <> | Subject | [PATCHv2] compiler: Don't perform compiletime_assert with -O0 | Date | Wed, 30 Aug 2017 11:02:36 -0700 |
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Recent changes[0] to make use of __compiletime_assert() from container_of() increased the usage of this macro, allowing developers to notice type conflicts in usage of container_of() at compile time. However, the implementation of __compiletime_assert relies on compiler optimizations to report an error. This means that if a developer uses "-O0" with any code that performs container_of(), the compiler will always report an error regardless of whether there is an actual problem in the code.
This patch disables compile_time_assert when optimizations are disabled to allow such code to compile with CFLAGS="-O0".
Example compilation failure:
./include/linux/compiler.h:547:38: error: call to ‘__compiletime_assert_94’ declared with attribute error: pointer type mismatch in container_of() _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^ ./include/linux/compiler.h:530:4: note: in definition of macro ‘__compiletime_assert’ prefix ## suffix(); \ ^~~~~~ ./include/linux/compiler.h:547:2: note: in expansion of macro ‘_compiletime_assert’ _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__) ^~~~~~~~~~~~~~~~~~~ ./include/linux/build_bug.h:46:37: note: in expansion of macro ‘compiletime_assert’ #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) ^~~~~~~~~~~~~~~~~~ ./include/linux/kernel.h:860:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’ BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \ ^~~~~~~~~~~~~~~~
[0] http://lkml.kernel.org/r/20170525120316.24473-7-abbotti@mev.co.uk
Signed-off-by: Joe Stringer <joe@ovn.org> Acked-by: Michal Nazarewicz <mina86@mina86.com> Cc: Ian Abbott <abbotti@mev.co.uk> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Kees Cook <keescook@chromium.org> Cc: Andrew Morton <akpm@linux-foundation.org> --- include/linux/compiler.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index eca8ad75e28b..b177fa2a4d69 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -517,7 +517,8 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s # define __compiletime_error_fallback(condition) do { } while (0) #endif -#define __compiletime_assert(condition, msg, prefix, suffix) \ +#ifdef __OPTIMIZE__ +# define __compiletime_assert(condition, msg, prefix, suffix) \ do { \ bool __cond = !(condition); \ extern void prefix ## suffix(void) __compiletime_error(msg); \ @@ -525,6 +526,10 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s prefix ## suffix(); \ __compiletime_error_fallback(__cond); \ } while (0) +#else +# define __compiletime_assert(condition, msg, prefix, suffix) \ + do { } while (0) +#endif #define _compiletime_assert(condition, msg, prefix, suffix) \ __compiletime_assert(condition, msg, prefix, suffix) -- 2.14.1
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