From: "Björn Töpel" <bjorn@kernel.org>
To: Pu Lehui <pulehui@huaweicloud.com>,
bpf@vger.kernel.org, linux-riscv@lists.infradead.org,
netdev@vger.kernel.org
Cc: Song Liu <song@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>, Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>, Palmer Dabbelt <palmer@dabbelt.com>,
Luke Nelson <luke.r.nels@gmail.com>,
Pu Lehui <pulehui@huawei.com>
Subject: Re: [PATCH bpf-next v2 4/4] riscv, bpf: Mixing bpf2bpf and tailcalls
Date: Thu, 01 Feb 2024 11:10:55 +0100 [thread overview]
Message-ID: <878r44mr4g.fsf@all.your.base.are.belong.to.us> (raw)
In-Reply-To: <fab22b9e-7b56-4fef-ba92-bf62ec43007d@huaweicloud.com>
Pu Lehui <pulehui@huaweicloud.com> writes:
>>> @@ -252,10 +220,7 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
>>> emit_ld(RV_REG_S5, store_offset, RV_REG_SP, ctx);
>>> store_offset -= 8;
>>> }
>>> - if (seen_reg(RV_REG_S6, ctx)) {
>>> - emit_ld(RV_REG_S6, store_offset, RV_REG_SP, ctx);
>>> - store_offset -= 8;
>>> - }
>>> + emit_ld(RV_REG_TCC, store_offset, RV_REG_SP, ctx);
>>
>> Why do you need to restore RV_REG_TCC? We're passing RV_REG_TCC (a6) as
>> an argument at all call-sites, and for tailcalls we're loading from the
>> stack.
>>
>> Is this to fake the a6 argument for the tail-call? If so, it's better to
>> move it to emit_bpf_tail_call(), instead of letting all programs pay for
>> it.
>
> Yes, we can remove this duplicate load. will do that at next version.
Hmm, no remove, but *move* right? Otherwise a6 can contain gargabe on
entering the tailcall?
Move it before __emit_epilogue() in the tailcall, no?
Björn
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next prev parent reply other threads:[~2024-02-01 10:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-30 4:09 [PATCH bpf-next v2 0/4] Mixing bpf2bpf and tailcalls for RV64 Pu Lehui
2024-01-30 4:09 ` [PATCH bpf-next v2 1/4] riscv, bpf: Remove redundant ctx->offset initialization Pu Lehui
2024-01-30 16:04 ` Björn Töpel
2024-01-30 4:09 ` [PATCH bpf-next v2 2/4] riscv, bpf: Using kvcalloc to allocate cache buffer Pu Lehui
2024-01-30 16:05 ` Björn Töpel
2024-01-30 4:09 ` [PATCH bpf-next v2 3/4] riscv, bpf: Add RV_TAILCALL_OFFSET macro to format tailcall offset Pu Lehui
2024-01-30 16:05 ` Björn Töpel
2024-01-30 4:09 ` [PATCH bpf-next v2 4/4] riscv, bpf: Mixing bpf2bpf and tailcalls Pu Lehui
2024-01-30 17:30 ` Björn Töpel
2024-02-01 8:22 ` Pu Lehui
2024-02-01 10:10 ` Björn Töpel [this message]
2024-02-01 12:10 ` Pu Lehui
2024-02-01 13:35 ` Björn Töpel
2024-02-02 9:44 ` Pu Lehui
2024-02-02 13:04 ` Björn Töpel
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