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

[Björn Töpel]

Björn Töpel <bjorn@xxxxxxxxxx> writes:

> Pu Lehui <pulehui@xxxxxxxxxxxxxxx> writes:
>
>> From: Pu Lehui <pulehui@xxxxxxxxxx>
>>
>> Add support sign-extension mov instructions for RV64.
>>
>> Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>
>> ---
>>  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.

Too quick! s/correct/incorrect/! :-)