[PATCH net-next] ARM: net: support BPF_ALU | BPF_MOD instructions in the BPF JIT.

[PATCH net-next] ARM: net: support BPF_ALU | BPF_MOD instructions in the BPF JIT.

[Nicolas Schichan]

For ARMv7 with UDIV instruction support, generate an UDIV instruction
followed by an MLS instruction.

For other ARM variants, generate code calling a C wrapper similar to
the jit_udiv() function used for BPF_ALU | BPF_DIV instructions.

Some performance numbers reported by the test_bpf module (the duration
per filter run is reported in nanoseconds, between "jitted:<x>" and
"PASS":

ARMv7 QEMU nojit:	test_bpf: #3 DIV_MOD_KX jited:0 2196 PASS
ARMv7 QEMU jit:		test_bpf: #3 DIV_MOD_KX jited:1 104 PASS
ARMv5 QEMU nojit:	test_bpf: #3 DIV_MOD_KX jited:0 2176 PASS
ARMv5 QEMU jit:		test_bpf: #3 DIV_MOD_KX jited:1 1104 PASS
ARMv5 kirkwood nojit:	test_bpf: #3 DIV_MOD_KX jited:0 1103 PASS
ARMv5 kirkwood jit:	test_bpf: #3 DIV_MOD_KX jited:1 311 PASS

Signed-off-by: Nicolas Schichan <nschichan@freebox.fr>
---
 arch/arm/net/bpf_jit_32.c | 38 ++++++++++++++++++++++++++++++++------
 arch/arm/net/bpf_jit_32.h |  5 +++++
 2 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 876060b..17214d9 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -125,7 +125,7 @@ static u64 jit_get_skb_w(struct sk_buff *skb, int offset)
 }
 
 /*
- * Wrapper that handles both OABI and EABI and assures Thumb2 interworking
+ * Wrappers that handles both OABI and EABI and assures Thumb2 interworking
  * (where the assembly routines like __aeabi_uidiv could cause problems).
  */
 static u32 jit_udiv(u32 dividend, u32 divisor)
@@ -133,6 +133,11 @@ static u32 jit_udiv(u32 dividend, u32 divisor)
 	return dividend / divisor;
 }
 
+static u32 jit_mod(u32 dividend, u32 divisor)
+{
+	return dividend % divisor;
+}
+
 static inline void _emit(int cond, u32 inst, struct jit_ctx *ctx)
 {
 	inst |= (cond << 28);
@@ -471,11 +476,17 @@ static inline void emit_blx_r(u8 tgt_reg, struct jit_ctx *ctx)
 #endif
 }
 
-static inline void emit_udiv(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx)
+static inline void emit_udivmod(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx,
+				int bpf_op)
 {
 #if __LINUX_ARM_ARCH__ == 7
 	if (elf_hwcap & HWCAP_IDIVA) {
-		emit(ARM_UDIV(rd, rm, rn), ctx);
+		if (bpf_op == BPF_DIV)
+			emit(ARM_UDIV(rd, rm, rn), ctx);
+		else {
+			emit(ARM_UDIV(ARM_R3, rm, rn), ctx);
+			emit(ARM_MLS(rd, rn, ARM_R3, rm), ctx);
+		}
 		return;
 	}
 #endif
@@ -496,7 +507,8 @@ static inline void emit_udiv(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx)
 		emit(ARM_MOV_R(ARM_R0, rm), ctx);
 
 	ctx->seen |= SEEN_CALL;
-	emit_mov_i(ARM_R3, (u32)jit_udiv, ctx);
+	emit_mov_i(ARM_R3, bpf_op == BPF_DIV ? (u32)jit_udiv : (u32)jit_mod,
+		   ctx);
 	emit_blx_r(ARM_R3, ctx);
 
 	if (rd != ARM_R0)
@@ -697,13 +709,27 @@ load_ind:
 			if (k == 1)
 				break;
 			emit_mov_i(r_scratch, k, ctx);
-			emit_udiv(r_A, r_A, r_scratch, ctx);
+			emit_udivmod(r_A, r_A, r_scratch, ctx, BPF_DIV);
 			break;
 		case BPF_ALU | BPF_DIV | BPF_X:
 			update_on_xread(ctx);
 			emit(ARM_CMP_I(r_X, 0), ctx);
 			emit_err_ret(ARM_COND_EQ, ctx);
-			emit_udiv(r_A, r_A, r_X, ctx);
+			emit_udivmod(r_A, r_A, r_X, ctx, BPF_DIV);
+			break;
+		case BPF_ALU | BPF_MOD | BPF_K:
+			if (k == 1) {
+				emit_mov_i(r_A, 0, ctx);
+				break;
+			}
+			emit_mov_i(r_scratch, k, ctx);
+			emit_udivmod(r_A, r_A, r_scratch, ctx, BPF_MOD);
+			break;
+		case BPF_ALU | BPF_MOD | BPF_X:
+			update_on_xread(ctx);
+			emit(ARM_CMP_I(r_X, 0), ctx);
+			emit_err_ret(ARM_COND_EQ, ctx);
+			emit_udivmod(r_A, r_A, r_X, ctx, BPF_MOD);
 			break;
 		case BPF_ALU | BPF_OR | BPF_K:
 			/* A |= K */
diff --git a/arch/arm/net/bpf_jit_32.h b/arch/arm/net/bpf_jit_32.h
index 4b17d5ab..c46fca2 100644
--- a/arch/arm/net/bpf_jit_32.h
+++ b/arch/arm/net/bpf_jit_32.h
@@ -115,6 +115,8 @@
 
 #define ARM_INST_UMULL		0x00800090
 
+#define ARM_INST_MLS		0x00600090
+
 /*
  * Use a suitable undefined instruction to use for ARM/Thumb2 faulting.
  * We need to be careful not to conflict with those used by other modules
@@ -210,4 +212,7 @@
 #define ARM_UMULL(rd_lo, rd_hi, rn, rm)	(ARM_INST_UMULL | (rd_hi) << 16 \
 					 | (rd_lo) << 12 | (rm) << 8 | rn)
 
+#define ARM_MLS(rd, rn, rm, ra)	(ARM_INST_MLS | (rd) << 16 | (rn) | (rm) << 8 \
+				 | (ra) << 12)
+
 #endif /* PFILTER_OPCODES_ARM_H */
-- 
1.9.1

Re: [PATCH net-next] ARM: net: support BPF_ALU | BPF_MOD instructions in the BPF JIT.

[Russell King - ARM Linux]

On Fri, Oct 02, 2015 at 04:37:51PM +0200, Nicolas Schichan wrote:
> @@ -125,7 +125,7 @@ static u64 jit_get_skb_w(struct sk_buff *skb, int offset)
>  }
>  
>  /*
> - * Wrapper that handles both OABI and EABI and assures Thumb2 interworking
> + * Wrappers that handles both OABI and EABI and assures Thumb2 interworking

That doesn't read right with "wrapper" becoming plural.

"Wrapper that handles ..."

or

"Wrappers which handle ..."

As normal, I'll let David pick the patch up, but please adjust the above
comment first, thanks.

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