linux-kernel - Re: [PATCH v2] riscv, bpf: Adapt bpf trampoline to optimized riscv ftrace framework

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Message-ID: <87sf9hgfob.fsf@all.your.base.are.belong.to.us>
Date:   Fri, 21 Jul 2023 22:42:12 +0200
From:   Björn Töpel <bjorn@...nel.org>
To:     Pu Lehui <pulehui@...weicloud.com>,
        linux-riscv@...ts.infradead.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        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>,
        Guo Ren <guoren@...nel.org>,
        Song Shuai <suagrfillet@...il.com>,
        Pu Lehui <pulehui@...wei.com>,
        Pu Lehui <pulehui@...weicloud.com>
Subject: Re: [PATCH v2] riscv, bpf: Adapt bpf trampoline to optimized riscv
 ftrace framework

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

> From: Pu Lehui <pulehui@...wei.com>
>
> Commit 6724a76cff85 ("riscv: ftrace: Reduce the detour code size to
> half") optimizes the detour code size of kernel functions to half with
> T0 register and the upcoming DYNAMIC_FTRACE_WITH_DIRECT_CALLS of riscv
> is based on this optimization, we need to adapt riscv bpf trampoline
> based on this. One thing to do is to reduce detour code size of bpf
> programs, and the second is to deal with the return address after the
> execution of bpf trampoline. Meanwhile, we need to construct the frame
> of parent function, otherwise we will miss one layer when unwinding.
> The related tests have passed.
>
> Signed-off-by: Pu Lehui <pulehui@...wei.com>

I'll do a proper review later (still on vacation), but I ran the
test_progs BPF selftest with the ftrace series [1] with this patch on
top.

81 more tests pass with [1] plus this patch, which is great!

Pre-patches [2], post-patches [3].

Feel free to add:
Tested-by: Björn Töpel <bjorn@...osinc.com>


Björn


[1] https://lore.kernel.org/linux-riscv/20230627111612.761164-1-suagrfillet@gmail.com/
[2] http://ix.io/4B9e
[3] http://ix.io/4B9f