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From: Eduard Zingerman <eddyz87@gmail.com>
To: "Jose E. Marchesi" <jose.marchesi@oracle.com>,
	Yonghong Song <yhs@meta.com>
Cc: bpf@vger.kernel.org
Subject: Re: Encoding of V4 32-bit JA
Date: Sun, 23 Jul 2023 20:10:15 +0300	[thread overview]
Message-ID: <32dc8c48803ff047266ee396fed3ccc9f7f0147e.camel@gmail.com> (raw)
In-Reply-To: <87a5vp6xvl.fsf@oracle.com>

On Fri, 2023-07-21 at 18:19 +0200, Jose E. Marchesi wrote:
> Hi Yonghong.
> 
> This is from the v4 instructions proposal:
> 
>     ========  =====  =========================  ============
>     code      value  description                notes
>     ========  =====  =========================  ============
>     BPF_JA    0x00   PC += imm                  BPF_JMP32 only
> 
> Is this instruction using source 1 instead of 0?  Otherwise, it would
> have exactly the same encoding than the V3< JA instruction.  Is that
> what is intended?
> 
> TIA.
> 

Hi Jose,

I think that assumption is that `BPF_JMP32 | BPF_JA` is currently free:
- documentation [1] implies that only `BPF_JMP` should be used for `BPF_JA`
  (see "notes" column for the first line)
- BPF verifier rejects `BPF_JMP32 | BPF_JA`
- clang always generates `BPF_JMP | BPF_JA`

Thanks,
Eduard

[1] https://www.kernel.org/doc/html/latest/bpf/instruction-set.html#jump-instructions

  reply	other threads:[~2023-07-23 17:10 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-21 16:19 Encoding of V4 32-bit JA Jose E. Marchesi
2023-07-23 17:10 ` Eduard Zingerman [this message]
2023-07-23 19:14   ` Jose E. Marchesi
2023-07-23 19:21     ` Eduard Zingerman
2023-07-23 19:57       ` Jose E. Marchesi
2023-07-23 23:51         ` Jose E. Marchesi
2023-07-24  2:37       ` Yonghong Song

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