netdev - Re: [PATCH bpf-next] libbpf: Ignore -Wformat-nonliteral warning

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Message-ID: <74b38291-f82d-b97c-bcb7-39762e86f0ae@fb.com>
Date:   Sun, 7 Apr 2019 06:11:25 +0000
From:   Yonghong Song <yhs@...com>
To:     Andrey Ignatov <rdna@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next] libbpf: Ignore -Wformat-nonliteral warning



On 4/6/19 10:37 PM, Andrey Ignatov wrote:
> vsprintf() in __base_pr() uses nonliteral format string and it breaks
> compilation for those who provide corresponding extra CFLAGS, e.g.:
> https://github.com/libbpf/libbpf/issues/27
> 
> If libbpf is built with the flags from PR:
> 
>    libbpf.c:68:26: error: format string is not a string literal
>    [-Werror,-Wformat-nonliteral]
>            return vfprintf(stderr, format, args);
>                                    ^~~~~~
>    1 error generated.
> 
> Ignore this warning since the use case in libbpf.c is legit.
> 
> Signed-off-by: Andrey Ignatov <rdna@...com>

Tested with clang compiler as well. It also resolved the same issue
when using clang to build libbpf in libbpf repo.
Acked-by: Yonghong Song <yhs@...com>

> ---
>   tools/lib/bpf/libbpf.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index e1e4d35cf08e..1ebfe7943d53 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -52,6 +52,11 @@
>   #define BPF_FS_MAGIC		0xcafe4a11
>   #endif
>   
> +/* vsprintf() in __base_pr() uses nonliteral format string. It may break
> + * compilation if user enables corresponding warning. Disable it explicitly.
> + */
> +#pragma GCC diagnostic ignored "-Wformat-nonliteral"
> +
>   #define __printf(a, b)	__attribute__((format(printf, a, b)))
>   
>   static int __base_pr(enum libbpf_print_level level, const char *format,
>