Re: [PATCH v4] ARM: net: JIT compiler for packet filters

Le jeudi 22 décembre 2011 à 13:59 +0100, Mircea Gherzan a écrit :

Based of Matt Evans's PPC64 implementation.

The compiler generates ARM instructions but interworking is
supported for Thumb2 kernels.

Supports both little and big endian. Unaligned loads are emitted
for ARMv6+. Not all the BPF opcodes that deal with ancillary data
are supported. The scratch memory of the filter lives on the stack.
Hardware integer division is used if it is available.

Enabled in the same way as for x86-64 and PPC64:

	echo 1 > /proc/sys/net/core/bpf_jit_enable

A value greater than 1 enables opcode output.

Signed-off-by: Mircea Gherzan <redacted>
---

...

+/*
+ * ABI:
+ *
+ * r0	scratch register
+ * r4	BPF register A
+ * r5	BPF register X
+ * r6	pointer to the skb
+ * r7	skb->data
+ * r8	skb_headlen(skb)
+ */
+
+#define r_scratch	ARM_R0
+/* r1-r3 are (also) used for the unaligned loads on the non-ARMv7 slowpath */
+#define r_off		ARM_R1
+#define r_A		ARM_R4
+#define r_X		ARM_R5
+#define r_skb		ARM_R6
+#define r_skb_data	ARM_R7
+#define r_skb_hl	ARM_R8
+
+#define SCRATCH_SP_OFFSET	0
+#define SCRATCH_OFF(k)		(SCRATCH_SP_OFFSET + (k))
+
+#define SEEN_MEM		((1 << BPF_MEMWORDS) - 1)
+#define SEEN_MEM_WORD(k)	(1 << (k))
+#define SEEN_X			(1 << BPF_MEMWORDS)
+#define SEEN_CALL		(1 << (BPF_MEMWORDS + 1))
+#define SEEN_DATA		(1 << (BPF_MEMWORDS + 2))

+#define SEEN_LEN		(1 << (BPF_MEMWORDS + 3))

This seems wrong. skb->len has nothing special, its a particular case of
skb dereferencing.

You should rename this to SEEN_SKB_REF, and use it for everything
needing r_skb :

+	if (ctx->seen & (SEEN_DATA | SEEN_LEN))
+		emit(ARM_MOV_R(r_skb, ARM_R0), ctx);
+

here you handled the thing correctly.

+		case BPF_S_LD_W_LEN:
+			ctx->seen |= SEEN_LEN;
+			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
+			emit(ARM_LDR_I(r_A, r_skb,
+				       offsetof(struct sk_buff, len)), ctx);
+			break;

but here there is a problem :

+		case BPF_S_ANC_PROTOCOL:
+			/* A = ntohs(skb->protocol) */
+			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
+						  protocol) != 2);
+			off = offsetof(struct sk_buff, protocol);
+			emit(ARM_LDRH_I(r_scratch, r_skb, off), ctx);
+			emit_swap16(r_A, r_scratch, ctx);
+			break;

here too :

+		case BPF_S_ANC_IFINDEX:
+			/* A = skb->dev->ifindex */
+			off = offsetof(struct sk_buff, dev);
+			emit(ARM_LDR_I(r_scratch, r_skb, off), ctx);
+
+			emit(ARM_CMP_I(r_scratch, 0), ctx);
+			emit_err_ret(ARM_COND_EQ, ctx);
+
+			BUILD_BUG_ON(FIELD_SIZEOF(struct net_device,
+						  ifindex) != 4);
+			off = offsetof(struct net_device, ifindex);
+			emit(ARM_LDR_I(r_A, r_scratch, off), ctx);
+			break;

here too :

+		case BPF_S_ANC_MARK:
+			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
+			off = offsetof(struct sk_buff, mark);
+			emit(ARM_LDR_I(r_A, r_skb, off), ctx);
+			break;

here too :

+		case BPF_S_ANC_RXHASH:
+			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, rxhash) != 4);
+			off = offsetof(struct sk_buff, rxhash);
+			emit(ARM_LDR_I(r_A, r_skb, off), ctx);
+			break;

and also here :

+		case BPF_S_ANC_QUEUE:
+			BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff,
+						  queue_mapping) != 2);
+			BUILD_BUG_ON(offsetof(struct sk_buff,
+					      queue_mapping) > 0xff);
+			off = offsetof(struct sk_buff, queue_mapping);
+			emit(ARM_LDRH_I(r_A, r_skb, off), ctx);
+			break;