linux-kernel - Re: [PATCH 2/4] test_bpf: Add test to make conditional jump cross a large number of insns.

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Message-ID: <59408139.6010302@iogearbox.net>
Date:   Wed, 14 Jun 2017 02:20:09 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     David Daney <david.daney@...ium.com>,
        Alexei Starovoitov <ast@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
CC:     linux-mips@...ux-mips.org, ralf@...ux-mips.org
Subject: Re: [PATCH 2/4] test_bpf: Add test to make conditional jump cross
 a large number of insns.

On 06/14/2017 01:49 AM, David Daney wrote:
> On MIPS, conditional branches can only span 32k instructions.  To
> exceed this limit in the JIT with the BPF maximum of 4k insns, we need
> to choose eBPF insns that expand to more than 8 machine instructions.
> Use BPF_LD_ABS as it is quite complex.  This forces the JIT to invert
> the sense of the branch to branch around a long jump to the end.
>
> This (somewhat) verifies that the branch inversion logic and target
> address calculation of the long jumps are done correctly.
>
> Signed-off-by: David Daney <david.daney@...ium.com>

Acked-by: Daniel Borkmann <daniel@...earbox.net>