Re: [PATCH bpf-next] libbpf: hashmap.h update to fix build issues using LLVM14

[sdf@google.com]

On 11/11, Eduard Zingerman wrote:
> A fix for the LLVM compilation error while building bpftool.
> Replaces the expression:

>    _Static_assert((p) == NULL || ...)

> by expression:

>    _Static_assert((__builtin_constant_p((p)) ? (p) == NULL : 0) || ...)

IIUC, when __builtin_constant_p(p) returns false, we just ignore the NULL  
check?
Do we have cases like that? If no, maybe it's safer to fail?

s/(p) == NULL : 0/(p) == NULL : 1/ ?

> When "p" is not a constant the former is not considered to be a
> constant expression by LLVM 14.

> The error was introduced in the following patch-set: [1].
> The error was reported here: [2].

> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>

> [1] https://lore.kernel.org/bpf/20221109142611.879983-1-eddyz87@gmail.com/
> [2] https://lore.kernel.org/all/202211110355.BcGcbZxP-lkp@intel.com/
> ---
>   tools/lib/bpf/hashmap.h   | 3 ++-
>   tools/perf/util/hashmap.h | 3 ++-
>   2 files changed, 4 insertions(+), 2 deletions(-)

> diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h
> index 3fe647477bad..0a5bf1937a7c 100644
> --- a/tools/lib/bpf/hashmap.h
> +++ b/tools/lib/bpf/hashmap.h
> @@ -123,7 +123,8 @@ enum hashmap_insert_strategy {
>   };

>   #define hashmap_cast_ptr(p) ({								\
> -	_Static_assert((p) == NULL || sizeof(*(p)) == sizeof(long),			\
> +	_Static_assert((__builtin_constant_p((p)) ? (p) == NULL : 0) ||			\
> +				sizeof(*(p)) == sizeof(long),				\
>   		       #p " pointee should be a long-sized integer or a pointer");	\
>   	(long *)(p);									\
>   })
> diff --git a/tools/perf/util/hashmap.h b/tools/perf/util/hashmap.h
> index 3fe647477bad..0a5bf1937a7c 100644
> --- a/tools/perf/util/hashmap.h
> +++ b/tools/perf/util/hashmap.h
> @@ -123,7 +123,8 @@ enum hashmap_insert_strategy {
>   };

>   #define hashmap_cast_ptr(p) ({								\
> -	_Static_assert((p) == NULL || sizeof(*(p)) == sizeof(long),			\
> +	_Static_assert((__builtin_constant_p((p)) ? (p) == NULL : 0) ||			\
> +				sizeof(*(p)) == sizeof(long),				\
>   		       #p " pointee should be a long-sized integer or a pointer");	\
>   	(long *)(p);									\
>   })
> --
> 2.34.1