linux-kernel - Re: [PATCH bpf-next 2/2] bpf,riscv: Implement bpf_addr_space

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Message-ID: <mb61pjzlslwp9.fsf@gmail.com>
Date: Sat, 23 Mar 2024 16:49:54 +0000
From: Puranjay Mohan <puranjay12@...il.com>
To: Pu Lehui <pulehui@...wei.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
 <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai
 Lau <martin.lau@...ux.dev>, "Eduard
 Zingerman" <eddyz87@...il.com>, Song Liu <song@...nel.org>, Yonghong Song
 <yonghong.song@...ux.dev>, 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>, Björn Töpel
 <bjorn@...nel.org>, Luke Nelson <luke.r.nels@...il.com>, Xi Wang
 <xi.wang@...il.com>, Paul Walmsley <paul.walmsley@...ive.com>, Palmer
 Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 bpf@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 2/2] bpf,riscv: Implement bpf_addr_space_cast
 instruction

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

> On 2024/3/23 23:46, Puranjay Mohan wrote:
>> LLVM generates bpf_addr_space_cast instruction while translating
> [snip]
>>   
>>   /* Convert from ninsns to bytes. */
>> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
>> index f51b832eafb6..3c389e75cb96 100644
>> --- a/arch/riscv/net/bpf_jit_comp64.c
>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>> @@ -1083,6 +1083,16 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>>   	/* dst = src */
>>   	case BPF_ALU | BPF_MOV | BPF_X:
>>   	case BPF_ALU64 | BPF_MOV | BPF_X:
>> +		if (BPF_CLASS(insn->code) == BPF_ALU64 && insn->off == BPF_ADDR_SPACE_CAST &&
>> +		    insn->imm == 1U << 16) {
>> +			emit_mv(RV_REG_T1, rs, ctx); > +			emit_zextw(RV_REG_T1, RV_REG_T1, ctx);
> combine mv and zextw will be better

Do you suggest doing:

emit_zextw(RV_REG_T1, rs, ctx);

Will do it in next version.

>> +			emit_imm(rd, (ctx->user_vm_start >> 32) << 32, ctx);
>> +			emit(rv_beq(RV_REG_T1, RV_REG_ZERO, 4), ctx);
>> +			emit_or(RV_REG_T1, rd, RV_REG_T1, ctx);
>> +			emit_mv(rd, RV_REG_T1, ctx);
> ditto, but for or and mv

How would we combine or and mv? 
also, we have a beq above and in one case both or and mv should happen,
but in other case only mv should happen.

Thanks,
Puranjay