From: Seth Forshee <seth.forshee@canonical.com>
To: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
bpf@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>
Subject: Re: [PATCH 2/5] s390/bpf: fix sign extension in branch_ku
Date: Fri, 17 Jul 2020 17:23:34 -0500 [thread overview]
Message-ID: <20200717222334.GQ3644@ubuntu-x1> (raw)
In-Reply-To: <20200717165326.6786-3-iii@linux.ibm.com>
On Fri, Jul 17, 2020 at 06:53:23PM +0200, Ilya Leoshkevich wrote:
> Both signed and unsigned variants of BPF_JMP | BPF_K require
> sign-extending the immediate. JIT emits cgfi for the signed case,
> which is correct, and clgfi for the unsigned case, which is not
> correct: clgfi zero-extends the immediate.
>
> s390 does not provide an instruction that does sign-extension and
> unsigned comparison at the same time. Therefore, fix by first loading
> the sign-extended immediate into work register REG_1 and proceeding
> as if it's BPF_X.
>
> Fixes: 4e9b4a6883dd ("s390/bpf: Use relative long branches")
> Reported-by: Seth Forshee <seth.forshee@canonical.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
This fixes the failing tests I was seeing. Thanks!
Tested-by: Seth Forshee <seth.forshee@canonical.com>
next prev parent reply other threads:[~2020-07-17 22:23 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 16:53 [PATCH 0/5] s390/bpf: fix lib/test_bpf.c failures Ilya Leoshkevich
2020-07-17 16:53 ` [PATCH 1/5] selftests: bpf: test_kmod.sh: fix running out of srctree Ilya Leoshkevich
2020-07-17 16:53 ` [PATCH 2/5] s390/bpf: fix sign extension in branch_ku Ilya Leoshkevich
2020-07-17 22:23 ` Seth Forshee [this message]
2020-07-17 16:53 ` [PATCH 3/5] s390/bpf: use brcl for jumping to exit_ip if necessary Ilya Leoshkevich
2020-07-17 16:53 ` [PATCH 4/5] s390/bpf: tolerate not converging code shrinking Ilya Leoshkevich
2020-07-17 16:53 ` [PATCH 5/5] s390/bpf: use bpf_skip() in bpf_jit_prologue() Ilya Leoshkevich
2020-07-21 18:17 ` [PATCH 0/5] s390/bpf: fix lib/test_bpf.c failures Alexei Starovoitov
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