net: filter: BPF 'JIT' compiler for PPC64

An implementation of a code generator for BPF programs to speed up packet
filtering on PPC64, inspired by Eric Dumazet's x86-64 version.

Filter code is generated as an ABI-compliant function in module_alloc()'d mem
with stackframe & prologue/epilogue generated if required (simple filters don't
need anything more than an li/blr).  The filter's local variables, M[], live in
registers.  Supports all BPF opcodes, although "complicated" loads from negative
packet offsets (e.g. SKF_LL_OFF) are not yet supported.

There are a couple of further optimisations left for future work; many-pass
assembly with branch-reach reduction and a register allocator to push M[]
variables into volatile registers would improve the code quality further.

This currently supports big-endian 64-bit PowerPC only (but is fairly simple
to port to PPC32 or LE!).

Enabled in the same way as x86-64:

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

Or, enabled with extra debug output:

	echo 2 > /proc/sys/net/core/bpf_jit_enable

Signed-off-by: Matt Evans <matt@ozlabs.org>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 227 insertions, 0 deletions

diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
new file mode 100644
index 000000000000..af1ab5e9a691
--- /dev/null
+++ b/arch/powerpc/net/bpf_jit.h
@@ -0,0 +1,227 @@
+/* bpf_jit.h: BPF JIT compiler for PPC64
+ *
+ * Copyright 2011 Matt Evans <matt@ozlabs.org>, IBM Corporation
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+#ifndef _BPF_JIT_H
+#define _BPF_JIT_H
+
+#define BPF_PPC_STACK_LOCALS	32
+#define BPF_PPC_STACK_BASIC	(48+64)
+#define BPF_PPC_STACK_SAVE	(18*8)
+#define BPF_PPC_STACKFRAME	(BPF_PPC_STACK_BASIC+BPF_PPC_STACK_LOCALS+ \
+				 BPF_PPC_STACK_SAVE)
+#define BPF_PPC_SLOWPATH_FRAME	(48+64)
+
+/*
+ * Generated code register usage:
+ *
+ * As normal PPC C ABI (e.g. r1=sp, r2=TOC), with:
+ *
+ * skb		r3	(Entry parameter)
+ * A register	r4
+ * X register	r5
+ * addr param	r6
+ * r7-r10	scratch
+ * skb->data	r14
+ * skb headlen	r15	(skb->len - skb->data_len)
+ * m[0]		r16
+ * m[...]	...
+ * m[15]	r31
+ */
+#define r_skb		3
+#define r_ret		3
+#define r_A		4
+#define r_X		5
+#define r_addr		6
+#define r_scratch1	7
+#define r_D		14
+#define r_HL		15
+#define r_M		16
+
+#ifndef __ASSEMBLY__
+
+/*
+ * Assembly helpers from arch/powerpc/net/bpf_jit.S:
+ */
+extern u8 sk_load_word[], sk_load_half[], sk_load_byte[], sk_load_byte_msh[];
+
+#define FUNCTION_DESCR_SIZE	24
+
+/*
+ * 16-bit immediate helper macros: HA() is for use with sign-extending instrs
+ * (e.g. LD, ADDI).  If the bottom 16 bits is "-ve", add another bit into the
+ * top half to negate the effect (i.e. 0xffff + 1 = 0x(1)0000).
+ */
+#define IMM_H(i)		((uintptr_t)(i)>>16)
+#define IMM_HA(i)		(((uintptr_t)(i)>>16) +			      \
+				 (((uintptr_t)(i) & 0x8000) >> 15))
+#define IMM_L(i)		((uintptr_t)(i) & 0xffff)
+
+#define PLANT_INSTR(d, idx, instr)					      \
+	do { if (d) { (d)[idx] = instr; } idx++; } while (0)
+#define EMIT(instr)		PLANT_INSTR(image, ctx->idx, instr)
+
+#define PPC_NOP()		EMIT(PPC_INST_NOP)
+#define PPC_BLR()		EMIT(PPC_INST_BLR)
+#define PPC_BLRL()		EMIT(PPC_INST_BLRL)
+#define PPC_MTLR(r)		EMIT(PPC_INST_MTLR | __PPC_RT(r))
+#define PPC_ADDI(d, a, i)	EMIT(PPC_INST_ADDI | __PPC_RT(d) |	      \
+				     __PPC_RA(a) | IMM_L(i))
+#define PPC_MR(d, a)		PPC_OR(d, a, a)
+#define PPC_LI(r, i)		PPC_ADDI(r, 0, i)
+#define PPC_ADDIS(d, a, i)	EMIT(PPC_INST_ADDIS |			      \
+				     __PPC_RS(d) | __PPC_RA(a) | IMM_L(i))
+#define PPC_LIS(r, i)		PPC_ADDIS(r, 0, i)
+#define PPC_STD(r, base, i)	EMIT(PPC_INST_STD | __PPC_RS(r) |	      \
+				     __PPC_RA(base) | ((i) & 0xfffc))
+
+#define PPC_LD(r, base, i)	EMIT(PPC_INST_LD | __PPC_RT(r) |	      \
+				     __PPC_RA(base) | IMM_L(i))
+#define PPC_LWZ(r, base, i)	EMIT(PPC_INST_LWZ | __PPC_RT(r) |	      \
+				     __PPC_RA(base) | IMM_L(i))
+#define PPC_LHZ(r, base, i)	EMIT(PPC_INST_LHZ | __PPC_RT(r) |	      \
+				     __PPC_RA(base) | IMM_L(i))
+/* Convenience helpers for the above with 'far' offsets: */
+#define PPC_LD_OFFS(r, base, i) do { if ((i) < 32768) PPC_LD(r, base, i);     \
+		else {	PPC_ADDIS(r, base, IMM_HA(i));			      \
+			PPC_LD(r, r, IMM_L(i)); } } while(0)
+
+#define PPC_LWZ_OFFS(r, base, i) do { if ((i) < 32768) PPC_LWZ(r, base, i);   \
+		else {	PPC_ADDIS(r, base, IMM_HA(i));			      \
+			PPC_LWZ(r, r, IMM_L(i)); } } while(0)
+
+#define PPC_LHZ_OFFS(r, base, i) do { if ((i) < 32768) PPC_LHZ(r, base, i);   \
+		else {	PPC_ADDIS(r, base, IMM_HA(i));			      \
+			PPC_LHZ(r, r, IMM_L(i)); } } while(0)
+
+#define PPC_CMPWI(a, i)		EMIT(PPC_INST_CMPWI | __PPC_RA(a) | IMM_L(i))
+#define PPC_CMPDI(a, i)		EMIT(PPC_INST_CMPDI | __PPC_RA(a) | IMM_L(i))
+#define PPC_CMPLWI(a, i)	EMIT(PPC_INST_CMPLWI | __PPC_RA(a) | IMM_L(i))
+#define PPC_CMPLW(a, b)		EMIT(PPC_INST_CMPLW | __PPC_RA(a) | __PPC_RB(b))
+
+#define PPC_SUB(d, a, b)	EMIT(PPC_INST_SUB | __PPC_RT(d) |	      \
+				     __PPC_RB(a) | __PPC_RA(b))
+#define PPC_ADD(d, a, b)	EMIT(PPC_INST_ADD | __PPC_RT(d) |	      \
+				     __PPC_RA(a) | __PPC_RB(b))
+#define PPC_MUL(d, a, b)	EMIT(PPC_INST_MULLW | __PPC_RT(d) |	      \
+				     __PPC_RA(a) | __PPC_RB(b))
+#define PPC_MULHWU(d, a, b)	EMIT(PPC_INST_MULHWU | __PPC_RT(d) |	      \
+				     __PPC_RA(a) | __PPC_RB(b))
+#define PPC_MULI(d, a, i)	EMIT(PPC_INST_MULLI | __PPC_RT(d) |	      \
+				     __PPC_RA(a) | IMM_L(i))
+#define PPC_DIVWU(d, a, b)	EMIT(PPC_INST_DIVWU | __PPC_RT(d) |	      \
+				     __PPC_RA(a) | __PPC_RB(b))
+#define PPC_AND(d, a, b)	EMIT(PPC_INST_AND | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | __PPC_RB(b))
+#define PPC_ANDI(d, a, i)	EMIT(PPC_INST_ANDI | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | IMM_L(i))
+#define PPC_AND_DOT(d, a, b)	EMIT(PPC_INST_ANDDOT | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | __PPC_RB(b))
+#define PPC_OR(d, a, b)		EMIT(PPC_INST_OR | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | __PPC_RB(b))
+#define PPC_ORI(d, a, i)	EMIT(PPC_INST_ORI | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | IMM_L(i))
+#define PPC_ORIS(d, a, i)	EMIT(PPC_INST_ORIS | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | IMM_L(i))
+#define PPC_SLW(d, a, s)	EMIT(PPC_INST_SLW | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | __PPC_RB(s))
+#define PPC_SRW(d, a, s)	EMIT(PPC_INST_SRW | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | __PPC_RB(s))
+/* slwi = rlwinm Rx, Ry, n, 0, 31-n */
+#define PPC_SLWI(d, a, i)	EMIT(PPC_INST_RLWINM | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | __PPC_SH(i) |	      \
+				     __PPC_MB(0) | __PPC_ME(31-(i)))
+/* srwi = rlwinm Rx, Ry, 32-n, n, 31 */
+#define PPC_SRWI(d, a, i)	EMIT(PPC_INST_RLWINM | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | __PPC_SH(32-(i)) |	      \
+				     __PPC_MB(i) | __PPC_ME(31))
+/* sldi = rldicr Rx, Ry, n, 63-n */
+#define PPC_SLDI(d, a, i)	EMIT(PPC_INST_RLDICR | __PPC_RA(d) |	      \
+				     __PPC_RS(a) | __PPC_SH(i) |	      \
+				     __PPC_MB(63-(i)) | (((i) & 0x20) >> 4))
+#define PPC_NEG(d, a)		EMIT(PPC_INST_NEG | __PPC_RT(d) | __PPC_RA(a))
+
+/* Long jump; (unconditional 'branch') */
+#define PPC_JMP(dest)		EMIT(PPC_INST_BRANCH |			      \
+				     (((dest) - (ctx->idx * 4)) & 0x03fffffc))
+/* "cond" here covers BO:BI fields. */
+#define PPC_BCC_SHORT(cond, dest)	EMIT(PPC_INST_BRANCH_COND |	      \
+					     (((cond) & 0x3ff) << 16) |	      \
+					     (((dest) - (ctx->idx * 4)) &     \
+					      0xfffc))
+#define PPC_LI32(d, i)		do { PPC_LI(d, IMM_L(i));		      \
+		if ((u32)(uintptr_t)(i) >= 32768) {			      \
+			PPC_ADDIS(d, d, IMM_HA(i));			      \
+		} } while(0)
+#define PPC_LI64(d, i)		do {					      \
+		if (!((uintptr_t)(i) & 0xffffffff00000000ULL))		      \
+			PPC_LI32(d, i);					      \
+		else {							      \
+			PPC_LIS(d, ((uintptr_t)(i) >> 48));		      \
+			if ((uintptr_t)(i) & 0x0000ffff00000000ULL)	      \
+				PPC_ORI(d, d,				      \
+					((uintptr_t)(i) >> 32) & 0xffff);     \
+			PPC_SLDI(d, d, 32);				      \
+			if ((uintptr_t)(i) & 0x00000000ffff0000ULL)	      \
+				PPC_ORIS(d, d,				      \
+					 ((uintptr_t)(i) >> 16) & 0xffff);    \
+			if ((uintptr_t)(i) & 0x000000000000ffffULL)	      \
+				PPC_ORI(d, d, (uintptr_t)(i) & 0xffff);	      \
+		} } while (0);
+
+static inline bool is_nearbranch(int offset)
+{
+	return (offset < 32768) && (offset >= -32768);
+}
+
+/*
+ * The fly in the ointment of code size changing from pass to pass is
+ * avoided by padding the short branch case with a NOP.	 If code size differs
+ * with different branch reaches we will have the issue of code moving from
+ * one pass to the next and will need a few passes to converge on a stable
+ * state.
+ */
+#define PPC_BCC(cond, dest)	do {					      \
+		if (is_nearbranch((dest) - (ctx->idx * 4))) {		      \
+			PPC_BCC_SHORT(cond, dest);			      \
+			PPC_NOP();					      \
+		} else {						      \
+			/* Flip the 'T or F' bit to invert comparison */      \
+			PPC_BCC_SHORT(cond ^ COND_CMP_TRUE, (ctx->idx+2)*4);  \
+			PPC_JMP(dest);					      \
+		} } while(0)
+
+/* To create a branch condition, select a bit of cr0... */
+#define CR0_LT		0
+#define CR0_GT		1
+#define CR0_EQ		2
+/* ...and modify BO[3] */
+#define COND_CMP_TRUE	0x100
+#define COND_CMP_FALSE	0x000
+/* Together, they make all required comparisons: */
+#define COND_GT		(CR0_GT | COND_CMP_TRUE)
+#define COND_GE		(CR0_LT | COND_CMP_FALSE)
+#define COND_EQ		(CR0_EQ | COND_CMP_TRUE)
+#define COND_NE		(CR0_EQ | COND_CMP_FALSE)
+#define COND_LT		(CR0_LT | COND_CMP_TRUE)
+
+#define SEEN_DATAREF 0x10000 /* might call external helpers */
+#define SEEN_XREG    0x20000 /* X reg is used */
+#define SEEN_MEM     0x40000 /* SEEN_MEM+(1<<n) = use mem[n] for temporary
+			      * storage */
+#define SEEN_MEM_MSK 0x0ffff
+
+struct codegen_context {
+	unsigned int seen;
+	unsigned int idx;
+	int pc_ret0; /* bpf index of first RET #0 instruction (if any) */
+};
+
+#endif
+
+#endif