Re: [PATCH bpf-next v1 1/2] resolve_btfids: Emit arena attributes from kfunc parameter suffixes

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

On Sun Aug 9, 2026 at 12:10 PM CEST, bot+bpf-ci wrote:
>> diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
>> index d2e4176339da..3c88ea192f7b 100644
>> --- a/tools/bpf/resolve_btfids/main.c
>> +++ b/tools/bpf/resolve_btfids/main.c
>
> [ ... ]
>
>> @@ -1067,6 +1070,22 @@ static int collect_decl_tags(struct btf2btf_context *ctx)
>>  	return 0;
>>  }
>>
>> +static bool param_name_has_suffix(const char *name, const char *suffix)
>> +{
>> +	size_t name_len = strlen(name);
>> +	size_t suffix_len = strlen(suffix);
>> +
>> +	return name_len >= suffix_len && !strcmp(name + name_len - suffix_len, suffix);
>> +}
>
> Should this be `name_len > suffix_len` instead of `name_len >= suffix_len`?
>
> The kernel's btf_param_match_suffix() in kernel/bpf/btf.c rejects a parameter
> whose name is exactly equal to the suffix:
>
> kernel/bpf/btf.c:btf_param_match_suffix() {
>     ...
>     len = strlen(param_name);
>     if (len <= suffix_len)
>         return false;
>     param_name += len - suffix_len;
>     return !strncmp(param_name, suffix, suffix_len);
> }
>
> That `len <= suffix_len` early return is what both is_kfunc_arg_arena() in
> kernel/bpf/verifier.c and btf_func_model_flags() in kernel/bpf/btf.c rely on.
> The same helper is also used by kernel/bpf/bpf_struct_ops.c for arena suffix
> matching.
>
> With the current implementation, a parameter named exactly "__arena" would be
> treated as an arena pointer by resolve_btfids (causing address_space(1) to be
> emitted in vmlinux.h), but would be treated as an ordinary kernel pointer by
> the verifier's is_kfunc_arg_arena().
>
> No in-tree kfunc currently uses a parameter named exactly "__arena" or
> "__arena__nullable" (checked kernel/bpf/arena.c, test_kmods/bpf_testmod.c,
> and btf_data.c), and the selftests added by commit 52b915d08490 only use
> names like "a__arena", so this would be a latent inconsistency rather than a
> currently-firing failure.
>

I think it's fine, won't matter in practice.

>> +
>> +static bool is_arena_param(const struct btf *btf, const struct btf_param *param)
>> +{
>> +	const char *name = btf__name_by_offset(btf, param->name_off);
>> +
>> +	return param_name_has_suffix(name, PARAM_SUFFIX_ARENA) ||
>> +	       param_name_has_suffix(name, PARAM_SUFFIX_ARENA_NULLABLE);
>> +}
>
> [ ... ]
>
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/31305217088