netdev - Re: [PATCH bpf 1/2] bpf, riscv: limit to 33 tail calls

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Message-ID: <CAJ+HfNiqtF9T-C7a1NoSekSAW+Fpr2kH2EghLDiRmf_+-Uat-w@mail.gmail.com>
Date:   Tue, 10 Dec 2019 07:31:26 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Paul Chaignon <paul.chaignon@...nge.com>
Cc:     Paul Burton <paulburton@...nel.org>,
        Mahshid Khezri <khezri.mahshid@...il.com>,
        paul.chaignon@...il.com, bpf <bpf@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH bpf 1/2] bpf, riscv: limit to 33 tail calls

On Mon, 9 Dec 2019 at 20:57, Björn Töpel <bjorn.topel@...il.com> wrote:
>
> On Mon, 9 Dec 2019 at 19:52, Paul Chaignon <paul.chaignon@...nge.com> wrote:
> >
> > All BPF JIT compilers except RISC-V's and MIPS' enforce a 33-tail calls
> > limit at runtime.  In addition, a test was recently added, in tailcalls2,
> > to check this limit.
> >
> > This patch updates the tail call limit in RISC-V's JIT compiler to allow
> > 33 tail calls.  I tested it using the above selftest on an emulated
> > RISCV64.
> >
>
> 33! ICK! ;-) Thanks for finding this!
>
> Acked-by: Björn Töpel <bjorn.topel@...il.com>
>

...and somewhat related; One of the tailcall tests fail due to missing
far-branch support in the emitter. I'll address this in the v2 of the
"far branch" series.