linux-kernel - Re: [PATCH bpf-next 3/7] riscv, bpf: Support sign-extension mov insns

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Message-ID: <490126e3-b5da-4523-11af-62a2a3c33514@huawei.com>
Date:   Thu, 24 Aug 2023 09:17:19 +0800
From:   Pu Lehui <pulehui@...wei.com>
To:     Björn Töpel <bjorn@...nel.org>,
        Pu Lehui <pulehui@...weicloud.com>,
        <linux-riscv@...ts.infradead.org>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     Yonghong Song <yhs@...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>,
        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>,
        Palmer Dabbelt <palmer@...belt.com>,
        Xu Kuohai <xukuohai@...wei.com>,
        Puranjay Mohan <puranjay12@...il.com>
Subject: Re: [PATCH bpf-next 3/7] riscv, bpf: Support sign-extension mov insns



On 2023/8/24 2:14, Björn Töpel wrote:
> Pu Lehui <pulehui@...weicloud.com> writes:
> 
>> From: Pu Lehui <pulehui@...wei.com>
>>
>> Add support sign-extension mov instructions for RV64.
>>
>> Signed-off-by: Pu Lehui <pulehui@...wei.com>
>> ---
>>   arch/riscv/net/bpf_jit_comp64.c | 14 +++++++++++++-
>>   1 file changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
>> index fd36cb17101a..d1497182cacf 100644
>> --- a/arch/riscv/net/bpf_jit_comp64.c
>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>> @@ -1047,7 +1047,19 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>>   			emit_zext_32(rd, ctx);
>>   			break;
>>   		}
>> -		emit_mv(rd, rs, ctx);
>> +		switch (insn->off) {
>> +		case 0:
>> +			emit_mv(rd, rs, ctx);
>> +			break;
>> +		case 8:
>> +		case 16:
>> +			emit_slli(rs, rs, 64 - insn->off, ctx);
>> +			emit_srai(rd, rs, 64 - insn->off, ctx);
> 
> You're clobbering the source register (rs) here, which is correct.

alright, will fix it

> 
> (Side note: Maybe it's time to add Zbb support to the JIT soon! ;-))
> 
> 
> Björn