[PATCH] ppc: bpf_jit: support MOD operation

[Matt Evans]

Hi Ben, Vladimir,


*dusts off very thick PPC cobwebs*  Sorry for the delay as I'm travelling, didn't get to this until now.

On 02/09/2013, at 9:45 PM, Benjamin Herrenschmidt wrote:

> On Mon, 2013-09-02 at 19:48 +0200, Vladimir Murzin wrote:
>> Ping
>> 
>> On Wed, Aug 28, 2013 at 02:49:52AM +0400, Vladimir Murzin wrote:
>>> commit b6069a9570 (filter: add MOD operation) added generic
>>> support for modulus operation in BPF.
>>> 
> Sorry, nobody got a chance to review that yet. Unfortunately Matt
> doesn't work for us anymore and none of us has experience with the
> BPF code, so somebody (possibly me) will need to spend a bit of time
> figuring it out before verifying that is correct.
> 
> Do you have a test case/suite by any chance ?
> 
> Ben.
> 
>>> This patch brings JIT support for PPC64
>>> 
>>> Signed-off-by: Vladimir Murzin <murzin.v at gmail.com>
>>> ---
>>> arch/powerpc/net/bpf_jit_comp.c | 22 ++++++++++++++++++++++
>>> 1 file changed, 22 insertions(+)
>>> 
>>> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
>>> index bf56e33..96f24dc 100644
>>> --- a/arch/powerpc/net/bpf_jit_comp.c
>>> +++ b/arch/powerpc/net/bpf_jit_comp.c
>>> @@ -193,6 +193,28 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image,
>>> 				PPC_MUL(r_A, r_A, r_scratch1);
>>> 			}
>>> 			break;
>>> +		case BPF_S_ALU_MOD_X: /* A %= X; */
>>> +			ctx->seen |= SEEN_XREG;
>>> +			PPC_CMPWI(r_X, 0);
>>> +			if (ctx->pc_ret0 != -1) {
>>> +				PPC_BCC(COND_EQ, addrs[ctx->pc_ret0]);
>>> +			} else {
>>> +				PPC_BCC_SHORT(COND_NE, (ctx->idx*4)+12);
>>> +				PPC_LI(r_ret, 0);
>>> +				PPC_JMP(exit_addr);
>>> +			}
>>> +			PPC_DIVWU(r_scratch1, r_A, r_X);
>>> +			PPC_MUL(r_scratch1, r_X, r_scratch1);
>>> +			PPC_SUB(r_A, r_A, r_scratch1);
>>> +			break;

Without having compiled & tested this, it looks fine to me (especially with the corrected DIVWU opcode in the other patch, oops...).

>>> +		case BPF_S_ALU_MOD_K: /* A %= K; */
>>> +#define r_scratch2 (r_scratch1 + 1)
>>> +			PPC_LI32(r_scratch2, K);
>>> +			PPC_DIVWU(r_scratch1, r_A, r_scratch2);
>>> +			PPC_MUL(r_scratch1, r_scratch2, r_scratch1);
>>> +			PPC_SUB(r_A, r_A, r_scratch1);
>>> +#undef r_scratch2
>>> +			break;

If you need another scratch register, it should really be defined in bpf_jit.h instead.

Once you define r_scratch2 in there,

Acked-by: Matt Evans <matt at ozlabs.org>


Thanks!


Matt




>>> 		case BPF_S_ALU_DIV_X: /* A /= X; */
>>> 			ctx->seen |= SEEN_XREG;
>>> 			PPC_CMPWI(r_X, 0);
>>> -- 
>>> 1.8.1.5
>>> 
>