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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Thu, 15 Apr 2021 16:11:35 -0700
Message-ID: <CAEf4Bzbt0hmhJVYGwc4wp+jp209ed75oUQcTXg-NTX5ABzFBzw@mail.gmail.com>
Subject: Re: [PATCH bpf-next v4 3/6] bpf: Add a bpf_snprintf helper
To:     Florent Revest <revest@chromium.org>
Cc:     bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Yonghong Song <yhs@fb.com>, KP Singh <kpsingh@kernel.org>,
        Brendan Jackman <jackmanb@chromium.org>,
        open list <linux-kernel@vger.kernel.org>
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On Wed, Apr 14, 2021 at 11:54 AM Florent Revest <revest@chromium.org> wrote:
>
> The implementation takes inspiration from the existing bpf_trace_printk
> helper but there are a few differences:
>
> To allow for a large number of format-specifiers, parameters are
> provided in an array, like in bpf_seq_printf.
>
> Because the output string takes two arguments and the array of
> parameters also takes two arguments, the format string needs to fit in
> one argument. Thankfully, ARG_PTR_TO_CONST_STR is guaranteed to point to
> a zero-terminated read-only map so we don't need a format string length
> arg.
>
> Because the format-string is known at verification time, we also do
> a first pass of format string validation in the verifier logic. This
> makes debugging easier.
>
> Signed-off-by: Florent Revest <revest@chromium.org>
> ---

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

>  include/linux/bpf.h            |  1 +
>  include/uapi/linux/bpf.h       | 28 +++++++++++++++++++
>  kernel/bpf/helpers.c           | 50 ++++++++++++++++++++++++++++++++++
>  kernel/bpf/verifier.c          | 41 ++++++++++++++++++++++++++++
>  kernel/trace/bpf_trace.c       |  2 ++
>  tools/include/uapi/linux/bpf.h | 28 +++++++++++++++++++
>  6 files changed, 150 insertions(+)
>

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