netdev - Re: [PATCH net-next v2] test_bpf: add similarly conflicting jump test case only for classic

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Message-Id: <20150527.141618.1170561992772984049.davem@davemloft.net>
Date:	Wed, 27 May 2015 14:16:18 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	daniel@...earbox.net
Cc:	netdev@...r.kernel.org, ast@...mgrid.com
Subject: Re: [PATCH net-next v2] test_bpf: add similarly conflicting jump
 test case only for classic

From: Daniel Borkmann <daniel@...earbox.net>
Date: Tue, 26 May 2015 22:35:43 +0200

> While 3b52960266a3 ("test_bpf: add more eBPF jump torture cases")
> added the int3 bug test case only for eBPF, which needs exactly 11
> passes to converge, here's a version for classic BPF with 11 passes,
> and one that would need 70 passes on x86_64 to actually converge for
> being successfully JITed. Effectively, all jumps are being optimized
> out resulting in a JIT image of just 89 bytes (from originally max
> BPF insns), only returning K.
> 
> Might be useful as a receipe for folks wanting to craft a test case
> when backporting the fix in commit 3f7352bf21f8 ("x86: bpf_jit: fix
> compilation of large bpf programs") while not having eBPF. The 2nd
> one is delegated to the interpreter as the last pass still results
> in shrinking, in other words, this one won't be JITed on x86_64.
> 
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>

Applied, thanks Daniel.
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