linux-kernel - Re: [PATCH] bpf: remove pointless code from bpf_do_trace

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Date:   Thu, 22 Apr 2021 17:46:53 +0200
From:   Florent Revest <revest@...omium.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alan Maguire <alan.maguire@...cle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH] bpf: remove pointless code from bpf_do_trace_printk()

On Thu, Apr 22, 2021 at 5:44 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Thu, Apr 22, 2021 at 8:35 AM Florent Revest <revest@...omium.org> wrote:
> > >
> > > I was having a stroll through lib/vsprintf.c and noticed bstr_printf:
> > >
> > >  * This function like C99 vsnprintf, but the difference is that vsnprintf gets
> > >  * arguments from stack, and bstr_printf gets arguments from @bin_buf which is
> > >  * a binary buffer that generated by vbin_printf.
> > >
> > > Maybe it would be easier to just build our argument buffer similarly
> > > to what vbin_printf does.
> >
> > I've been experimenting with this idea and it is quite promising :) it
> > also makes the code much cleaner, I find. I'll send a series asap.
>
> You mean to use bstr_printf internally ? That could work indeed.
> Make sure CONFIG_BINARY_PRINTF is selected.
> CONFIG_TRACING does it already.

Yes :)

> > BPF maintainers: should we fix forward or do you prefer reverting the
> > snprintf series and then re-applying another snprintf series without
> > the regression in bpf_trace_printk that mangles some argument types ?
> > (bpf_seq_printf has always been like that so no regression there)
>
> Pls send it as a follow up.
> Along with another patch to clean verifier bits we discussed.
> The merge window is approaching, so it has to be done asap.

On it ;)