netdev - Re: [PATCH v2 bpf-next 3/3] selftests/bpf: add variable-length data concat pattern less than test

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Message-ID: <CAEf4BzZFPoqdvVBdyqY=t9Ccfvf-_VysJ7UR9L9qQ5-SxdPeKg@mail.gmail.com>
Date:   Mon, 22 Jun 2020 19:28:57 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        john fastabend <john.fastabend@...il.com>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 3/3] selftests/bpf: add variable-length data
 concat pattern less than test

On Mon, Jun 22, 2020 at 5:31 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Mon, Jun 22, 2020 at 05:09:04PM -0700, Andrii Nakryiko wrote:
> > Extend original variable-length tests with a case to catch a common
> > existing pattern of testing for < 0 for errors. Note because
> > verifier also tracks upper bounds and we know it can not be greater
> > than MAX_LEN here we can skip upper bound check.
> >
> > In ALU64 enabled compilation converting from long->int return types
> > in probe helpers results in extra instruction pattern, <<= 32, s >>= 32.
> > The trade-off is the non-ALU64 case works. If you really care about
> > every extra insn (XDP case?) then you probably should be using original
> > int type.
> >
> > In addition adding a sext insn to bpf might help the verifier in the
> > general case to avoid these types of tricks.
> >
> > Signed-off-by: John Fastabend <john.fastabend@...il.com>
>
> Please keep John's 'Author:' on the patch.
> git commit --author= --amend
> or keep 'From:' when you applied to your local git.

I manually re-did the patch, because it wasn't applying cleanly. I'll
use --author, though, I didn't know about it, thanks.

> Also add your SOB after John's.
> Even if you didn't change the patch at all.
> Same thing if you've reworked the patch.

ok, will do