From: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>
To: "Yazhou Tang" <tangyazhou@zju.edu.cn>, <bpf@vger.kernel.org>,
<ast@kernel.org>, <eddyz87@gmail.com>
Cc: <daniel@iogearbox.net>, <john.fastabend@gmail.com>,
<andrii@kernel.org>, <martin.lau@linux.dev>, <song@kernel.org>,
<yonghong.song@linux.dev>, <kpsingh@kernel.org>,
<sdf@fomichev.me>, <haoluo@google.com>, <jolsa@kernel.org>,
<tangyazhou518@outlook.com>, <shenghaoyuan0928@163.com>,
<ziye@zju.edu.cn>
Subject: Re: [RFC PATCH bpf-next 1/6] bpf: Add UHMUL and SHMUL instructions
Date: Mon, 07 Sep 2026 12:51:18 -0700 [thread overview]
Message-ID: <DL9CGP0NFZ37.25Y31VZH6PKPQ@gmail.com> (raw)
In-Reply-To: <20260902070534.2141812-2-tangyazhou@zju.edu.cn>
On Wed Sep 2, 2026 at 12:05 AM PDT, Yazhou Tang wrote:
> From: Tianci Cao <ziye@zju.edu.cn>
>
> Define UHMUL and SHMUL as BPF_ALU64 BPF_MUL variants selected by insn->off.
> UHMUL returns the high 64 bits of an unsigned 64-by-64-bit product, while
> SHMUL returns the high 64 bits of a signed product. Keep off == 0 as the
> existing low-half multiplication, and assign off == 1 and off == 2 to
> UHMUL and SHMUL, respectively.
>
> These operations are inspired by the UHMUL and SHMUL instructions
> introduced as part of the PQR instruction class in Solana sBPF[1].
>
> The encoding and immediate semantics differ from current sBPF.
>
> 1. Solana sBPF assigns these operations dedicated opcodes in the BPF_PQR
> class, whereas this implementation selects them through the offset
> field of BPF_MUL.
>
> 2. Solana sBPF initially sign-extended the immediate operand of UHMUL,
> but later changed unsigned PQR immediates, including UHMUL, to be
> zero-extended[2].
Why did you switch to zero-extend ?
Sounds odd to do zero extend just for these ops.
Overall the patch set look pretty good.
Please drop RFC and respin.
next prev parent reply other threads:[~2026-09-07 19:51 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-02 7:05 [RFC PATCH bpf-next 0/6] bpf: Add UHMUL and SHMUL instructions Yazhou Tang
2026-09-02 7:05 ` [RFC PATCH bpf-next 1/6] " Yazhou Tang
2026-09-07 19:51 ` Alexei Starovoitov [this message]
2026-09-08 8:30 ` Yazhou Tang
2026-09-12 3:40 ` Alexei Starovoitov
2026-09-02 7:05 ` [RFC PATCH bpf-next 2/6] bpf, x86: JIT UHMUL and SHMUL on x86-64 Yazhou Tang
2026-09-02 7:05 ` [RFC PATCH bpf-next 3/6] bpf: Reject UHMUL/SHMUL in unsupported JITs Yazhou Tang
2026-09-02 7:21 ` sashiko-bot
2026-09-02 8:09 ` Yazhou Tang
2026-09-07 19:53 ` Alexei Starovoitov
2026-09-08 8:32 ` Yazhou Tang
2026-09-02 7:05 ` [RFC PATCH bpf-next 4/6] bpf: Refactor ALU instruction variant validation Yazhou Tang
2026-09-02 7:05 ` [RFC PATCH bpf-next 5/6] bpf: Add verifier support for UHMUL and SHMUL Yazhou Tang
2026-09-02 7:05 ` [RFC PATCH bpf-next 6/6] selftests/bpf: Add bytecode tests " Yazhou Tang
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