Re: [PATCH bpf-next v3] bpftool: Compute map size of light skeletons at runtime

[Leon Hwang <leon.hwang@linux.dev>]

On 2026/9/16 00:28, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Low] bpf: compilation failure in skel_internal.h due to non-standard roundup macro
> --
> 
> commit cf9410def9715a95832e67f7002ebd4dabf2d7ad
> Author: Leon Hwang <leon.hwang@linux.dev>
> 
> bpftool: Compute map size of light skeletons at runtime
> 
> This commit addresses an issue with generating light skeletons on
> a host with a different page size from the target. It accomplishes
> this by passing the original map dimensions and dynamically computing
> the mmap size at runtime.
> 
>> diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h
>> index 1f3f332dffbe9..9e16b8e8cb7c9 100644
>> --- a/tools/lib/bpf/skel_internal.h
>> +++ b/tools/lib/bpf/skel_internal.h
> [ ... ]
>> @@ -193,25 +197,39 @@ static inline void skel_free(void *p)
>>  	free(p);
>>  }
>>  
>> -static inline void skel_free_map_data(void *p, __u64 addr, size_t sz)
>> +static inline size_t skel_map_mmap_sz(size_t val_sz, __u32 max_entries)
>>  {
>> -	munmap(p, sz);
>> +	const long page_sz = sysconf(_SC_PAGE_SIZE);
>> +	size_t mmap_sz;
>> +
>> +	mmap_sz = roundup(val_sz, 8) * max_entries;
>> +	mmap_sz = roundup(mmap_sz, page_sz);
> 
> [Severity: Low]
> Does this code rely on the non-standard roundup macro from <sys/param.h>?
> 
> When users include the generated light skeleton header in a project compiled
> with strict C standards (e.g., -std=c99 or -std=c11) without _DEFAULT_SOURCE
> or _GNU_SOURCE, the roundup macro might not be defined. This can cause a
> compilation error due to an implicit declaration of function.

False positive.

By looking into the source code of <sys/param.h>, there's no
_DEFAULT_SOURCE or _GNU_SOURCE guard for the roundup macro.

Thanks,
Leon