[Bpf] Re: [PATCH] bpftool: Fix -Wuninitialized-const-pointer warnings with clang >= 21

[Quentin Monnet <[e-mail]>]

2025-09-16 23:11 UTC-0700 ~ Tom Stellard
<tstellar=[e-mail]>
> This fixes the build with -Werror -Wall.
> 
> btf_dumper.c:71:31: error: variable 'finfo' is uninitialized when passed as a const pointer argument here [-Werror,-Wuninitialized-const-pointer]
>    71 |         info.func_info = ptr_to_u64(&finfo);
>       |                                      ^~~~~
> 
> prog.c:2294:31: error: variable 'func_info' is uninitialized when passed as a const pointer argument here [-Werror,-Wuninitialized-const-pointer]
>  2294 |         info.func_info = ptr_to_u64(&func_info);
>       |
> 
> Signed-off-by: Tom Stellard <[e-mail]>


Hi, thanks for this!

If you want to contribute this patch to bpftool, I'd recommend sending
it to the kernel BPF mailing list [0], rather than the IETF BPF mailing
list, and making sure to add the maintainers in copy [1].


[0]
https://docs.kernel.org/bpf/bpf_devel_QA.html#q-to-which-mailing-list-do-i-need-to-submit-my-bpf-patches
[1] From kernel repo: ./scripts/get_maintainer.pl tools/bpf/bpftool/


> ---
>  tools/bpf/bpftool/btf_dumper.c | 2 ++
>  tools/bpf/bpftool/prog.c       | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
> index 4e896d8a2416..363d3e592ce2 100644
> --- a/tools/bpf/bpftool/btf_dumper.c
> +++ b/tools/bpf/bpftool/btf_dumper.c
> @@ -68,6 +68,8 @@ static int dump_prog_id_as_func_ptr(const struct btf_dumper *d,
>  	memset(&info, 0, sizeof(info));
>  	info.nr_func_info = 1;
>  	info.func_info_rec_size = finfo_rec_size;
> +	/* Silence -Wuninitialized-const-pointer warning in clang >= 21. */
> +	memset(&finfo,  0, sizeof(finfo));


How about simply initialising the variable when we declare it, instead?

	struct bpf_func_info finfo = {};

This would avoid adding the memset() and comment in the middle of the
function, and keep it slightly more readable?

Same for prog.c.

Best regards,
Quentin