linux-kernel - Re: [PATCH] bpf: add __printf() to for printf fmt strings

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Date:   Wed, 22 Nov 2023 16:26:51 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Ben Dooks <ben.dooks@...ethink.co.uk>, bpf@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: add __printf() to for printf fmt strings

On 11/22/23 2:36 PM, Ben Dooks wrote:
> The btf_seq_show() and btf_snprintf_show() take a printk format
> string so add a __printf() to these two functions. This fixes the
> following extended warnings:
> 
> kernel/bpf/btf.c:7094:29: error: function ‘btf_seq_show’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
> kernel/bpf/btf.c:7131:9: error: function ‘btf_snprintf_show’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
> 
> Signed-off-by: Ben Dooks <ben.dooks@...ethink.co.uk>
> ---
>   kernel/bpf/btf.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 15d71d2986d3..46c2e87c383d 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -7088,8 +7088,8 @@ static void btf_type_show(const struct btf *btf, u32 type_id, void *obj,
>   	btf_type_ops(t)->show(btf, t, type_id, obj, 0, show);
>   }
>   
> -static void btf_seq_show(struct btf_show *show, const char *fmt,
> -			 va_list args)
> +static __printf(2,0) void btf_seq_show(struct btf_show *show, const char *fmt,
> +				       va_list args)
>   {
>   	seq_vprintf((struct seq_file *)show->target, fmt, args);
>   }
> @@ -7122,7 +7122,7 @@ struct btf_show_snprintf {
>   	int len;		/* length we would have written */
>   };
>   
> -static void btf_snprintf_show(struct btf_show *show, const char *fmt,
> +static __printf(2,0) void btf_snprintf_show(struct btf_show *show, const char *fmt,
>   			      va_list args)
>   {

Looks good, only small nit is to fix up kernel-style formatting wrt spacing.

>   	struct btf_show_snprintf *ssnprintf = (struct btf_show_snprintf *)show;
>