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

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Message-Id: <7664a4d2-ed4e-4e60-2d1d-3b113d05972b@linux.ibm.com>
Date:   Wed, 5 Dec 2018 12:07:54 +0530
From:   Sandipan Das <sandipan@...ux.ibm.com>
To:     Jiong Wang <jiong.wang@...ronome.com>
Cc:     daniel@...earbox.net, ast@...nel.org, netdev@...r.kernel.org,
        oss-drivers@...ronome.com,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>
Subject: Re: [PATCH bpf-next 2/7] ppc: bpf: implement jitting of BPF_ALU |
 BPF_ARSH | BPF_*

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 <naveen.n.rao@...ux.ibm.com>
> Cc: Sandipan Das <sandipan@...ux.ibm.com>
> Signed-off-by: Jiong Wang <jiong.wang@...ronome.com>
> ---
[...]
> 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.

>  		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