netdev - Re: [RFC PATCH bpf-next v1 00/14] MIPS: eBPF: refactor code, add MIPS32 JIT

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Date:   Tue, 20 Jul 2021 10:47:46 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Johan Almbladh <johan.almbladh@...finetworks.com>
Cc:     Tony Ambardar <tony.ambardar@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, linux-mips@...r.kernel.org,
        Hassan Naveed <hnaveed@...ecomp.com>,
        David Daney <ddaney@...iumnetworks.com>,
        Luke Nelson <luke.r.nels@...il.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>
Subject: Re: [RFC PATCH bpf-next v1 00/14] MIPS: eBPF: refactor code, add
 MIPS32 JIT

On Mon, Jul 19, 2021 at 6:25 PM Johan Almbladh
<johan.almbladh@...finetworks.com> wrote:
>
> I have been focusing on the code the last couple of weeks so I didn't
> see your email until now. I am sure that this comes as much of a
> surprise to you as it did to me. Anyway, can send a patch with my JIT
> implementation tomorrow.

It is surprising to have not one but two mips32 JITs :)
I really hope you folks can figure out the common path forward.
It sounds to me that the register mapping choices in both
implementations are the same (which would be the most debated
part to agree on).
Not seeing Johan's patches it's hard to make any comparison.
So far I like Tony's patches. The refactoring and code sharing is great.

Tony,
what 'static analysis' by the JIT you're referring to?
re: bpf_jit_needs_zext issue between JIT and the verifier.
It's a difficult one.
opt_subreg_zext_lo32_rnd_hi32() shouldn't depend on JIT
(other than bpf_jit_needs_zext).
But you're setting that callback the same way as x86-32 JIT.
So the same bug should be seen there too.
Could you double check if it's the case?
It's either a regression (if both x86-32 and mips32 JITs fail
this test_verifier test) or endianness related (if it's mip32 JIT only).

Thank you both for the exciting work!