Getting rid of cast-align warning for one specific case

Question

I'm using this implementation of container_of on arm:

#define container_of(ptr, type, member)                 \
({                              \
    const typeof(((type *) NULL)->member) *__mptr = (ptr);  \
    (type *) (void*)((char *) __mptr - offsetof(type, member)); \
})

The problem is that not even adding (void*) cast to this implementation gets rid of the -Wcast-align warning. I really don't want to have to turn it off just because it fails in this one specific case where it is in fact ok. (the problem is that casting to char* and then to type* changes alignment of the type. A solution that has been used before is to first cast to void* and then to type* as a way of telling the compiler that it is intentional - but this solution does not work for me on gcc version 4.8.3 (OpenWrt/Linaro GCC 4.8-2014.04 r48666)

Is there a way to tell compiler to allow this cast just here?

Not sure what you mean. Casting a pointer does **not** change aligment on ARM. — too honest for this site, Sep 07 '16 at 23:20
Ok, got it now. You could try `_Pragma` to temporarily disable the warning. — too honest for this site, Sep 07 '16 at 23:22
In order to program robust precompiler macros, you should wrap every instance of every macro argument in parentheses. Does it help you to write ...((Type)*)... etc.? I would remove the additional (void*) casts behind ((Type)*), too. — HelpingHand, Apr 07 '20 at 14:56

Getting rid of cast-align warning for one specific case

0 Answers0