From: Quentin Monnet <qmo@kernel.org>
To: Simone Magnani <simone.magnani@isovalent.com>, bpf@vger.kernel.org
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org,
yonghong.song@linux.dev, john.fastabend@gmail.com,
kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com,
jolsa@kernel.org, nathan@kernel.org, ndesaulniers@google.com,
morbo@google.com, justinstitt@google.com,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH bpf-next v2] bpftool: Probe for ISA v4 instruction set extension
Date: Mon, 9 Dec 2024 17:05:57 +0000 [thread overview]
Message-ID: <98c2ad67-2672-4eef-b952-18e6ad28a027@kernel.org> (raw)
In-Reply-To: <ca871055-0b4c-4380-8f32-a4a7152345c6@isovalent.com>
2024-12-09 18:01 UTC+0100 ~ Simone Magnani <simone.magnani@isovalent.com>
> On 09/12/24 16:20, Quentin Monnet wrote:
>> Looking again at the probe itself, does the second instruction serve any
>> practical purpose here? Don't you just need to test the BPF_JMP32_A?
>>
>> Looks good otherwise, thank you!
>>
>> Reviewed-by: Quentin Monnet <qmo@kernel.org>
>
> I wanted to keep probes similar to the previous ones (especially v3
> and v2), despite we never check their return codes. This means
> having as 4th instruction `BPF_MOV64_IMM(BPF_REG_0, 1)`. However,
> to do so, I also need the 2nd instruction, otherwise I'd hit an
> `Invalid Argument` error while calling `bpf_prog_load()`: I think
> that would be due to the fact that no execution paths would
> execute that instruction otherwise.
Right, that's what I missed.
>
> An alternative approach less consistent with the others would be:
>
> struct bpf_insn insns[3] = {
> BPF_MOV64_IMM(BPF_REG_0, 0),
> BPF_JMP32_A(0),
> BPF_EXIT_INSN()
> };
>
> Please let me know if you have any further questions, need
> additional information, or if I could improve the patch.
No it's all good to me in that case, thank you!
Quentin
next prev parent reply other threads:[~2024-12-09 17:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20241209102644.29880-1-simone.magnani@isovalent.com>
2024-12-09 14:54 ` [PATCH bpf-next v2] bpftool: Probe for ISA v4 instruction set extension Simone Magnani
2024-12-09 15:20 ` Quentin Monnet
2024-12-09 17:01 ` Simone Magnani
2024-12-09 17:05 ` Quentin Monnet [this message]
2024-12-12 16:40 ` patchwork-bot+netdevbpf
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