1/* bpf_jit.S: Packet/header access helper functions
  2 * for PPC64 BPF compiler.
  3 *
  4 * Copyright 2011 Matt Evans <matt@ozlabs.org>, IBM Corporation
  5 *
  6 * This program is free software; you can redistribute it and/or
  7 * modify it under the terms of the GNU General Public License
  8 * as published by the Free Software Foundation; version 2
  9 * of the License.
 10 */
 11
 12#include <asm/ppc_asm.h>
 13#include "bpf_jit.h"
 14
 15/*
 16 * All of these routines are called directly from generated code,
 17 * whose register usage is:
 18 *
 19 * r3		skb
 20 * r4,r5	A,X
 21 * r6		*** address parameter to helper ***
 22 * r7-r10	scratch
 23 * r14		skb->data
 24 * r15		skb headlen
 25 * r16-31	M[]
 26 */
 27
 28/*
 29 * To consider: These helpers are so small it could be better to just
 30 * generate them inline.  Inline code can do the simple headlen check
 31 * then branch directly to slow_path_XXX if required.  (In fact, could
 32 * load a spare GPR with the address of slow_path_generic and pass size
 33 * as an argument, making the call site a mtlr, li and bllr.)
 34 *
 35 * Technically, the "is addr < 0" check is unnecessary & slowing down
 36 * the ABS path, as it's statically checked on generation.
 37 */
 38	.globl	sk_load_word
 39sk_load_word:
 40	cmpdi	r_addr, 0
 41	blt	bpf_error
 42	/* Are we accessing past headlen? */
 43	subi	r_scratch1, r_HL, 4
 44	cmpd	r_scratch1, r_addr
 45	blt	bpf_slow_path_word
 46	/* Nope, just hitting the header.  cr0 here is eq or gt! */
 47	lwzx	r_A, r_D, r_addr
 48	/* When big endian we don't need to byteswap. */
 49	blr	/* Return success, cr0 != LT */
 50
 51	.globl	sk_load_half
 52sk_load_half:
 53	cmpdi	r_addr, 0
 54	blt	bpf_error
 55	subi	r_scratch1, r_HL, 2
 56	cmpd	r_scratch1, r_addr
 57	blt	bpf_slow_path_half
 58	lhzx	r_A, r_D, r_addr
 59	blr
 60
 61	.globl	sk_load_byte
 62sk_load_byte:
 63	cmpdi	r_addr, 0
 64	blt	bpf_error
 65	cmpd	r_HL, r_addr
 66	ble	bpf_slow_path_byte
 67	lbzx	r_A, r_D, r_addr
 68	blr
 69
 70/*
 71 * BPF_S_LDX_B_MSH: ldxb  4*([offset]&0xf)
 72 * r_addr is the offset value, already known positive
 73 */
 74	.globl sk_load_byte_msh
 75sk_load_byte_msh:
 76	cmpd	r_HL, r_addr
 77	ble	bpf_slow_path_byte_msh
 78	lbzx	r_X, r_D, r_addr
 79	rlwinm	r_X, r_X, 2, 32-4-2, 31-2
 80	blr
 81
 82bpf_error:
 83	/* Entered with cr0 = lt */
 84	li	r3, 0
 85	/* Generated code will 'blt epilogue', returning 0. */
 86	blr
 87
 88/* Call out to skb_copy_bits:
 89 * We'll need to back up our volatile regs first; we have
 90 * local variable space at r1+(BPF_PPC_STACK_BASIC).
 91 * Allocate a new stack frame here to remain ABI-compliant in
 92 * stashing LR.
 93 */
 94#define bpf_slow_path_common(SIZE)				\
 95	mflr	r0;						\
 96	std	r0, 16(r1);					\
 97	/* R3 goes in parameter space of caller's frame */	\
 98	std	r_skb, (BPF_PPC_STACKFRAME+48)(r1);		\
 99	std	r_A, (BPF_PPC_STACK_BASIC+(0*8))(r1);		\
100	std	r_X, (BPF_PPC_STACK_BASIC+(1*8))(r1);		\
101	addi	r5, r1, BPF_PPC_STACK_BASIC+(2*8);		\
102	stdu	r1, -BPF_PPC_SLOWPATH_FRAME(r1);		\
103	/* R3 = r_skb, as passed */				\
104	mr	r4, r_addr;					\
105	li	r6, SIZE;					\
106	bl	skb_copy_bits;					\
107	/* R3 = 0 on success */					\
108	addi	r1, r1, BPF_PPC_SLOWPATH_FRAME;			\
109	ld	r0, 16(r1);					\
110	ld	r_A, (BPF_PPC_STACK_BASIC+(0*8))(r1);		\
111	ld	r_X, (BPF_PPC_STACK_BASIC+(1*8))(r1);		\
112	mtlr	r0;						\
113	cmpdi	r3, 0;						\
114	blt	bpf_error;	/* cr0 = LT */			\
115	ld	r_skb, (BPF_PPC_STACKFRAME+48)(r1);		\
116	/* Great success! */
117
118bpf_slow_path_word:
119	bpf_slow_path_common(4)
120	/* Data value is on stack, and cr0 != LT */
121	lwz	r_A, BPF_PPC_STACK_BASIC+(2*8)(r1)
122	blr
123
124bpf_slow_path_half:
125	bpf_slow_path_common(2)
126	lhz	r_A, BPF_PPC_STACK_BASIC+(2*8)(r1)
127	blr
128
129bpf_slow_path_byte:
130	bpf_slow_path_common(1)
131	lbz	r_A, BPF_PPC_STACK_BASIC+(2*8)(r1)
132	blr
133
134bpf_slow_path_byte_msh:
135	bpf_slow_path_common(1)
136	lbz	r_X, BPF_PPC_STACK_BASIC+(2*8)(r1)
137	rlwinm	r_X, r_X, 2, 32-4-2, 31-2
138	blr