1/* bpf_jit.S : BPF JIT helper functions
2 *
3 * Copyright (C) 2011 Eric Dumazet (eric.dumazet@gmail.com)
4 *
5 * This program is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU General Public License
7 * as published by the Free Software Foundation; version 2
8 * of the License.
9 */
10#include <linux/linkage.h>
11#include <asm/dwarf2.h>
12
13/*
14 * Calling convention :
15 * rdi : skb pointer
16 * esi : offset of byte(s) to fetch in skb (can be scratched)
17 * r8  : copy of skb->data
18 * r9d : hlen = skb->len - skb->data_len
19 */
20#define SKBDATA	%r8
21
22sk_load_word_ind:
23	.globl	sk_load_word_ind
24
25	add	%ebx,%esi	/* offset += X */
26#	test    %esi,%esi	/* if (offset < 0) goto bpf_error; */
27	js	bpf_error
28
29sk_load_word:
30	.globl	sk_load_word
31
32	mov	%r9d,%eax		# hlen
33	sub	%esi,%eax		# hlen - offset
34	cmp	$3,%eax
35	jle	bpf_slow_path_word
36	mov     (SKBDATA,%rsi),%eax
37	bswap   %eax  			/* ntohl() */
38	ret
39
40
41sk_load_half_ind:
42	.globl sk_load_half_ind
43
44	add	%ebx,%esi	/* offset += X */
45	js	bpf_error
46
47sk_load_half:
48	.globl	sk_load_half
49
50	mov	%r9d,%eax
51	sub	%esi,%eax		#	hlen - offset
52	cmp	$1,%eax
53	jle	bpf_slow_path_half
54	movzwl	(SKBDATA,%rsi),%eax
55	rol	$8,%ax			# ntohs()
56	ret
57
58sk_load_byte_ind:
59	.globl sk_load_byte_ind
60	add	%ebx,%esi	/* offset += X */
61	js	bpf_error
62
63sk_load_byte:
64	.globl	sk_load_byte
65
66	cmp	%esi,%r9d   /* if (offset >= hlen) goto bpf_slow_path_byte */
67	jle	bpf_slow_path_byte
68	movzbl	(SKBDATA,%rsi),%eax
69	ret
70
71/**
72 * sk_load_byte_msh - BPF_S_LDX_B_MSH helper
73 *
74 * Implements BPF_S_LDX_B_MSH : ldxb  4*([offset]&0xf)
75 * Must preserve A accumulator (%eax)
76 * Inputs : %esi is the offset value, already known positive
77 */
78ENTRY(sk_load_byte_msh)
79	CFI_STARTPROC
80	cmp	%esi,%r9d      /* if (offset >= hlen) goto bpf_slow_path_byte_msh */
81	jle	bpf_slow_path_byte_msh
82	movzbl	(SKBDATA,%rsi),%ebx
83	and	$15,%bl
84	shl	$2,%bl
85	ret
86	CFI_ENDPROC
87ENDPROC(sk_load_byte_msh)
88
89bpf_error:
90# force a return 0 from jit handler
91	xor		%eax,%eax
92	mov		-8(%rbp),%rbx
93	leaveq
94	ret
95
96/* rsi contains offset and can be scratched */
97#define bpf_slow_path_common(LEN)		\
98	push	%rdi;    /* save skb */		\
99	push	%r9;				\
100	push	SKBDATA;			\
101/* rsi already has offset */			\
102	mov	$LEN,%ecx;	/* len */	\
103	lea	-12(%rbp),%rdx;			\
104	call	skb_copy_bits;			\
105	test    %eax,%eax;			\
106	pop	SKBDATA;			\
107	pop	%r9;				\
108	pop	%rdi
109
110
111bpf_slow_path_word:
112	bpf_slow_path_common(4)
113	js	bpf_error
114	mov	-12(%rbp),%eax
115	bswap	%eax
116	ret
117
118bpf_slow_path_half:
119	bpf_slow_path_common(2)
120	js	bpf_error
121	mov	-12(%rbp),%ax
122	rol	$8,%ax
123	movzwl	%ax,%eax
124	ret
125
126bpf_slow_path_byte:
127	bpf_slow_path_common(1)
128	js	bpf_error
129	movzbl	-12(%rbp),%eax
130	ret
131
132bpf_slow_path_byte_msh:
133	xchg	%eax,%ebx /* dont lose A , X is about to be scratched */
134	bpf_slow_path_common(1)
135	js	bpf_error
136	movzbl	-12(%rbp),%eax
137	and	$15,%al
138	shl	$2,%al
139	xchg	%eax,%ebx
140	ret
141