netdev - Re: [PATCH v5 bpf-next 06/10] tracepoint: compute num

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Date:   Mon, 26 Mar 2018 17:27:19 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Alexei Starovoitov <ast@...com>
Cc:     rostedt <rostedt@...dmis.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        netdev <netdev@...r.kernel.org>,
        kernel-team <kernel-team@...com>,
        linux-api <linux-api@...r.kernel.org>,
        "Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [PATCH v5 bpf-next 06/10] tracepoint: compute num_args at build
 time

----- On Mar 26, 2018, at 1:55 PM, Alexei Starovoitov ast@...com wrote:

[...]

> 
> correct. this set deals with in-kernel tracepoints only.
> No attempt to do anything with tracepoints inside modules.

Please endeavor to handle in-module tracepoints properly, then we'll
be able to pursue a more constructive discussion.

[...]

> Also I hope you noticed that the patch is doing:
> +++ b/include/linux/tracepoint-defs.h
> @@ -33,6 +33,7 @@ struct tracepoint {
>         int (*regfunc)(void);
>         void (*unregfunc)(void);
>         struct tracepoint_func __rcu *funcs;
> +       u32 num_args;
>  };
> 
> To make sure that bpf programs are safe I need to do a static check
> in the verifier that programs don't access arguments beyond
> those specified by the tracepoint.
> 
> That was mentioned in the commit log of patch 6 too:
> "
> compute number of arguments passed into tracepoint
> at compile time and store it as part of 'struct tracepoint'.
> The number is necessary to check safety of bpf program access that
> is coming in subsequent patch.
> "

This part of the patch and its associated changelog is fine
with me. Please submit it as a separate commit from the rest
of the tracepoint.{c,h} changes.

[...]

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com