Re: [PATCH perf] perf: Fix btf_vlen() signedness errors

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [Medium] Silent truncation of BTF_INFO_VLEN in libbpf's btf_vlen()
--

commit c28608c8a13cb7af8bf42f5aaadf102bb452fc40
Author: Alan Maguire <alan.maguire@oracle.com>

perf: Fix btf_vlen() signedness errors

This commit updates perf to use unsigned int loop counters when
iterating up to btf_vlen(). This avoids signedness errors after commit
f7a6b9eaff3e6 extended the BTF UAPI vlen to use previously unused bits.

> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 48615ddccd93a..9903d79c4b77a 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -964,7 +964,7 @@ static bool syscall_arg__strtoul_btf_enum(char *bf, size_t size, struct syscall_
>  	struct btf *btf = arg->trace->btf;
>  	struct btf_enum *be = btf_enum(bt);
>  
> -	for (int i = 0; i < btf_vlen(bt); ++i, ++be) {
> +	for (unsigned int i = 0; i < btf_vlen(bt); ++i, ++be) {

[Severity: Medium]
This is a pre-existing issue, but does the btf_vlen function still silently
truncate the newly extended length?

Looking at tools/lib/bpf/btf.h, it appears to be defined as:

static inline __u16 btf_vlen(const struct btf_type *t)
{
        return BTF_INFO_VLEN(t->info);
}

Since commit f7a6b9eaff3e6 extended the internal BTF_INFO_VLEN from 16 to
24 bits to support more than 65535 elements, won't returning __u16 here
truncate the upper 8 bits?

While updating the loop variables to unsigned int fixes the signedness
warnings in consumers, does the underlying library still need an update to
return __u32 and prevent truncation?

>  		const char *name = btf__name_by_offset(btf, be->name_off);
>  		int max_len = max(size, strlen(name));

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260622103418.579115-1-alan.maguire@oracle.com?part=1