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