From: Song Liu <songliubraving@fb.com>
To: Yonghong Song <yhs@fb.com>
Cc: bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@fb.com>,
"Daniel Borkmann" <daniel@iogearbox.net>,
Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH bpf-next v2] [tools/bpf] workaround a verifier failure for test_progs
Date: Thu, 7 Nov 2019 23:10:10 +0000 [thread overview]
Message-ID: <BDA6DC5F-1C36-4E62-967E-43FA0DCC6231@fb.com> (raw)
In-Reply-To: <20191107170045.2503480-1-yhs@fb.com>
> On Nov 7, 2019, at 9:00 AM, Yonghong Song <yhs@fb.com> wrote:
>
[...]
> Let us workaound this issue until we found a compiler and/or
> verifier solution. The workaround in this patch is
> to make variable 'ret' volatile, which will force a reload
> and then '&' operation to ensure better value range.
> With this patch, I got the below byte code for the loop,
> 0000000000000328 LBB0_9:
> 101: r4 = r10
> 102: r4 += -288
> 103: r4 += r7
> 104: w8 &= 255
> 105: r1 = r10
> 106: r1 += -488
> 107: r1 += r8
> 108: r2 = 7
> 109: r3 = 0
> 110: call 106
> 111: *(u32 *)(r10 - 64) = r0
> 112: r1 = *(u32 *)(r10 - 64)
> 113: if w1 s< 1 goto -28 <LBB0_5>
> 114: r1 = *(u32 *)(r10 - 64)
> 115: if w1 s> 7 goto -30 <LBB0_5>
> 116: r1 = *(u32 *)(r10 - 64)
> 117: w1 &= 7
> 118: w1 += w8
> 119: r7 += 8
> 120: w8 = w1
> 121: if r7 != 224 goto -21 <LBB0_9>
> Insn 117 did the '&' operation and we got more precise
> value range for 'w8' at insn 120.
Thanks for adding this information.
> The test is happy then.
> #3/17 test_sysctl_loop1.o:OK
>
> Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
next prev parent reply other threads:[~2019-11-07 23:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-07 17:00 [PATCH bpf-next v2] [tools/bpf] workaround a verifier failure for test_progs Yonghong Song
2019-11-07 23:10 ` Song Liu [this message]
2019-11-11 13:07 ` Daniel Borkmann
2020-04-28 2:56 Ma Xinjian
2020-04-28 6:13 ` Yonghong Song
2020-04-28 22:33 ` Alexei Starovoitov
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