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: <20200623003119.onlwey7ko5z6heyq@ast-mbp.dhcp.thefacebook.com>
Date:   Mon, 22 Jun 2020 17:31:19 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
        daniel@...earbox.net, john.fastabend@...il.com,
        andrii.nakryiko@...il.com, 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 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.
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.