From: "Jose E. Marchesi" <jose.marchesi@oracle.com>
To: Eduard Zingerman <eddyz87@gmail.com>
Cc: Yonghong Song <yhs@meta.com>, bpf@vger.kernel.org
Subject: Re: Encoding of V4 32-bit JA
Date: Sun, 23 Jul 2023 21:57:55 +0200 [thread overview]
Message-ID: <871qgyqu2k.fsf@oracle.com> (raw)
In-Reply-To: <ee97e19d73fa460bc37004baf01bd5f9fe6f67b4.camel@gmail.com> (Eduard Zingerman's message of "Sun, 23 Jul 2023 22:21:19 +0300")
> On Sun, 2023-07-23 at 21:14 +0200, Jose E. Marchesi wrote:
>> > 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`
>>
>> Makes sense, thanks for the info.
>>
>> Do you know the precise pseudo-c assembly syntax to use for this
>> instruction?
>
> In [1] Yonghong uses the following form:
>
> gotol +0xcd9b
>
> But it seems to be not specified in the documentation for the patch-set v3.
I will use that syntax in binutils for now.
> [1] https://reviews.llvm.org/D144829
>
>>
>> > Thanks,
>> > Eduard
>> >
>> > [1] https://www.kernel.org/doc/html/latest/bpf/instruction-set.html#jump-instructions
next prev parent reply other threads:[~2023-07-23 19:58 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
2023-07-23 19:14 ` Jose E. Marchesi
2023-07-23 19:21 ` Eduard Zingerman
2023-07-23 19:57 ` Jose E. Marchesi [this message]
2023-07-23 23:51 ` Jose E. Marchesi
2023-07-24 2:37 ` Yonghong Song
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