Re: [PATCH] compiler: Don't perform compiletime_assert with -O0.
From: Joe Stringer
Date: Wed Aug 30 2017 - 14:03:44 EST
On 30 August 2017 at 03:26, Michal Nazarewicz <mina86@xxxxxxxxxx> wrote:
> 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 â__compiletime_assert_94â 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 â__compiletime_assertâ
>> prefix ## suffix(); \
>> ^~~~~~
>> ./include/linux/compiler.h:547:2: note: in expansion of macro â_compiletime_assertâ
>> _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
>> ^~~~~~~~~~~~~~~~~~~
>> ./include/linux/build_bug.h:46:37: note: in expansion of macro âcompiletime_assertâ
>> #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>> ^~~~~~~~~~~~~~~~~~
>> ./include/linux/kernel.h:860:2: note: in expansion of macro âBUILD_BUG_ON_MSGâ
>> BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
>> ^~~~~~~~~~~~~~~~
>>
>> [0] http://lkml.kernel.org/r/20170525120316.24473-7-abbotti@xxxxxxxxx
>>
>> Signed-off-by: Joe Stringer <joe@xxxxxxx>
>> Cc: Ian Abbott <abbotti@xxxxxxxxx>
>> Cc: Arnd Bergmann <arnd@xxxxxxxx>
>> Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> ---
>> 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 <mina86@xxxxxxxxxx>
Thanks, I applied this change and send a v2 with your ack.