linux-kernel - Re: [PATCH bpf v2] riscv, bpf: Emit fixed-length instructions for BPF_PSEUDO

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Message-ID: <87359szzw3.fsf@all.your.base.are.belong.to.us>
Date:   Tue, 06 Dec 2022 09:42:52 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Pu Lehui <pulehui@...weicloud.com>, bpf@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Pu Lehui <pulehui@...wei.com>
Subject: Re: [PATCH bpf v2] riscv, bpf: Emit fixed-length instructions for
 BPF_PSEUDO_FUNC

Pu Lehui <pulehui@...weicloud.com> writes:

>> Wouldn't that work?
>> 
>
> It definitely works. But auipc+addi may be some holes, while 
> lui+addi+slli support all the address of kernel and module. And this 
> might be help for the future feature porting.

We're already using auipc/jalr for calls, and I'd say it *very* unlikely
that we'll hit the non-covered range. I'd say go with auipc/addi +
error, and we can change if this really is a problem.