linux-hardening - Re: [PATCH v1 02/13] libbpf: Make _

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Date: Mon, 11 Mar 2024 10:49:17 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Ian Rogers <irogers@...gle.com>
Cc: Arnd Bergmann <arnd@...db.de>, Andrii Nakryiko <andrii@...nel.org>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
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	Mark Rutland <mark.rutland@....com>, 
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	linux-arch@...r.kernel.org, bpf@...r.kernel.org, 
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	linux-kselftest@...r.kernel.org, linux-hardening@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: Re: [PATCH v1 02/13] libbpf: Make __printf define conditional

On Sat, Mar 9, 2024 at 6:05 PM Ian Rogers <irogers@...gle.com> wrote:
>
> libbpf depends upon linux/err.h which has a linux/compiler.h
> dependency. In the kernel includes, as opposed to the tools version,
> linux/compiler.h includes linux/compiler_attributes.h which defines
> __printf. As the libbpf.c __printf definition isn't guarded by an
> ifndef, this leads to a duplicate definition compilation error when
> trying to update the tools/include/linux/compiler.h. Fix this by
> adding the missing ifndef.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/lib/bpf/libbpf.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index afd09571c482..2152360b4b18 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -66,7 +66,9 @@
>   */
>  #pragma GCC diagnostic ignored "-Wformat-nonliteral"
>
> -#define __printf(a, b) __attribute__((format(printf, a, b)))
> +#ifndef __printf
> +# define __printf(a, b)        __attribute__((format(printf, a, b)))

styling nit: don't add spaces between # and define, please

overall LGTM

Acked-by: Andrii Nakryiko <andrii@...nel.org>

Two questions, though.

1. It seems like just dropping #define __printf in libbpf.c compiles
fine (I checked both building libbpf directly, and BPF selftest, and
perf, and bpftool directly, all of them built fine). So we can
probably just drop this. I'll need to add __printf on Github, but
that's fine.

2. Logistics. Which tree should this patch go through? Can I land it
in bpf-next or it's too much inconvenience for you?


> +#endif
>
>  static struct bpf_map *bpf_object__add_map(struct bpf_object *obj);
>  static bool prog_is_subprog(const struct bpf_object *obj, const struct bpf_program *prog);
> --
> 2.44.0.278.ge034bb2e1d-goog
>