On Tue, Aug 29 2017, Joe Stringer wrote:
> 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/[email protected]
>
> Signed-off-by: Joe Stringer <[email protected]>
> Cc: Ian Abbott <[email protected]>
> Cc: Arnd Bergmann <[email protected]>
> Cc: Michal Nazarewicz <[email protected]>
> Cc: Kees Cook <[email protected]>
> Cc: Andrew Morton <[email protected]>
> ---
> include/linux/compiler.h | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index eca8ad75e28b..b67e5ec9b810 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 +526,9 @@ 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)
+# define __compiletime_assert(condition, msg, prefix, suffix) \
+ do { } while (0)
With that fix,
Acked-by: Michal Nazarewicz <[email protected]>
> +#endif
>
> #define _compiletime_assert(condition, msg, prefix, suffix) \
> __compiletime_assert(condition, msg, prefix, suffix)
--
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ
«If at first you don’t succeed, give up skydiving»
