All of lore.kernel.org
 help / color / mirror / Atom feed
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>




  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=BDA6DC5F-1C36-4E62-967E-43FA0DCC6231@fb.com \
    --to=songliubraving@fb.com \
    --cc=Kernel-team@fb.com \
    --cc=ast@fb.com \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=yhs@fb.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.