Re: [PATCH v1 1/1] bpf: Mark bpf_stream_vprintk_impl() with __printf() attribute

[Alexei Starovoitov]

On Tue, Dec 9, 2025 at 12:49 AM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> bpf_stream_vprintk_impl() is using printf() type of format, and compiler
> is not happy about them as is:
>
> kernel/bpf/stream.c:241:9: error: function ‘bpf_stream_vprintk_impl’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
>   241 |         ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt__str, data.bin_args);
>       |         ^~~
>
> Fix the compilation errors by adding __printf() attribute.
>
> Fixes: 5ab154f1463a ("bpf: Introduce BPF standard streams")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> ---
>  kernel/bpf/stream.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
> index 0b6bc3f30335..4bff72e3c16f 100644
> --- a/kernel/bpf/stream.c
> +++ b/kernel/bpf/stream.c
> @@ -212,6 +212,7 @@ __bpf_kfunc_start_defs();
>   * Avoid using enum bpf_stream_id so that kfunc users don't have to pull in the
>   * enum in headers.
>   */
> +__printf(2, 0)
>  __bpf_kfunc int bpf_stream_vprintk_impl(int stream_id, const char *fmt__str, const void *args,

same issue.
The addition of this attribute doesn't make any difference, since kfunc
protos are autogenerated from BTF and it's not there.

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