Subject: Re: [PATCH bpf-next 2/7] ppc: bpf: implement jitting of BPF_ALU | BPF_ARSH | BPF_*

From: Jiong Wang <[email-masked]>
Date: Wed, 05 Dec 2018 11:28:32 +0000

Sandipan Das writes:

> Hi Jiong,
>
> On 05/12/18 2:25 AM, Jiong Wang wrote:
>> This patch implements code-gen for BPF_ALU | BPF_ARSH | BPF_*.
>> 
>> Cc: Naveen N. Rao <[email-masked]>
>> Cc: Sandipan Das <[email-masked]>
>> Signed-off-by: Jiong Wang <[email-masked]>
>> ---
> [...]
>> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
>> index 17482f5..c685b4f 100644
>> --- a/arch/powerpc/net/bpf_jit_comp64.c
>> +++ b/arch/powerpc/net/bpf_jit_comp64.c
>> @@ -529,9 +529,15 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
>>  			if (imm != 0)
>>  				PPC_SRDI(dst_reg, dst_reg, imm);
>>  			break;
>> +		case BPF_ALU | BPF_ARSH | BPF_X: /* (s32) dst >>= src */
>> +			PPC_SRAW(dst_reg, dst_reg, src_reg);
>> +			break;
>
> On ppc64, the sraw and srawi instructions also use sign extension. So, you will have
> to ensure that upper 32 bits are cleared. We already have a label in our JIT code
> called bpf_alu32_trunc that takes care of this. Replacing the break statement with
> a goto bpf_alu32_trunc will fix this.

(resend the reply, got a delivery failure notification from
[email-masked])

Indeed. Doubled checked the ISA doc,"Bit 32 of RS is replicated to fill
RA0:31.".

Will fix both places in v2.

Thanks

Regards,
Jiong

>
>>  		case BPF_ALU64 | BPF_ARSH | BPF_X: /* (s64) dst >>= src */
>>  			PPC_SRAD(dst_reg, dst_reg, src_reg);
>>  			break;
>> +		case BPF_ALU | BPF_ARSH | BPF_K: /* (s32) dst >>= imm */
>> +			PPC_SRAWI(dst_reg, dst_reg, imm);
>> +			break;
>
> Same here.
>
>>  		case BPF_ALU64 | BPF_ARSH | BPF_K: /* (s64) dst >>= imm */
>>  			if (imm != 0)
>>  				PPC_SRADI(dst_reg, dst_reg, imm);
>> 
>
> With Regards,
> Sandipan