summaryrefslogtreecommitdiff
path: root/src/arch/i386/lib/walkcbfs.S
blob: 395c46e20c3790686d8a9475330893aa45948288 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
#define CBFS_HEADER_PTR 0xfffffffc

#define CBFS_HEADER_MAGIC 0
#define CBFS_HEADER_VERSION (CBFS_HEADER_MAGIC + 4)
#define CBFS_HEADER_ROMSIZE (CBFS_HEADER_VERSION + 4)
#define CBFS_HEADER_BOOTBLOCKSIZE (CBFS_HEADER_ROMSIZE + 4)
#define CBFS_HEADER_ALIGN (CBFS_HEADER_BOOTBLOCKSIZE + 4)
#define CBFS_HEADER_OFFSET (CBFS_HEADER_ALIGN + 4)

#define CBFS_FILE_MAGIC 0
#define CBFS_FILE_LEN (CBFS_FILE_MAGIC + 8)
#define CBFS_FILE_TYPE (CBFS_FILE_LEN + 4)
#define CBFS_FILE_CHECKSUM (CBFS_FILE_TYPE + 4)
#define CBFS_FILE_OFFSET (CBFS_FILE_CHECKSUM + 4)

#define CBFS_FILE_STRUCTSIZE (CBFS_FILE_OFFSET + 4)

#define CBFS_STAGE_COMPRESSION 0
#define CBFS_STAGE_ENTRY (CBFS_STAGE_COMPRESSION + 4)
#define CBFS_STAGE_LOAD (CBFS_STAGE_ENTRY + 8)
#define CBFS_STAGE_LEN (CBFS_STAGE_LOAD + 8)
#define CBFS_STAGE_MEMLEN (CBFS_STAGE_LEN + 4)

/*
  input %esi: filename
  input %esp: return address (not pointer to return address!)
  output %eax: entry point
  clobbers %ebx, %ecx, %edi
*/
walkcbfs:
	cld

	mov CBFS_HEADER_PTR, %eax
	mov CBFS_HEADER_ROMSIZE(%eax), %ecx
	bswap %ecx
	mov $0, %ebx
	sub %ecx, %ebx
	mov CBFS_HEADER_OFFSET(%eax), %ecx
	bswap %ecx
	add %ecx, %ebx

	/* determine filename length */
	mov $0, %eax
1:
	cmpb $0, (%eax,%esi)
	jz 2f
	add $1, %eax
	jmp 1b
2:
	add $1, %eax
walker:
	mov 0(%ebx), %edi
	cmp %edi, filemagic
	jne searchfile
	mov 4(%ebx), %edi
	cmp %edi, filemagic+4
	jne searchfile

	mov %ebx, %edi
	add $CBFS_FILE_STRUCTSIZE, %edi /* edi = address of first byte after struct cbfs_file */
	mov %eax, %ecx
	repe cmpsb
	# zero flag set if strings are equal
	jnz tryharder

	# we found it!
	mov CBFS_FILE_OFFSET(%ebx), %eax
	bswap %eax
	add %ebx, %eax
	add $CBFS_STAGE_ENTRY, %eax /* eax = ((cbfs_stage* (cbfs_file* ebx)->offset)->entry) */
	mov 0(%eax), %eax
	jmp *%esp

tryharder:
	sub %ebx, %edi
	sub $CBFS_FILE_STRUCTSIZE, %edi /* edi = # of walked bytes */
	sub %edi, %esi /* esi = start of filename */

	/* ebx = ecx = (current+offset+len+ALIGN-1) & ~(ALIGN-1) */
	mov CBFS_FILE_OFFSET(%ebx), %ecx
	bswap %ecx
	add %ebx, %ecx
	mov CBFS_FILE_LEN(%ebx), %edi
	bswap %edi
	add %edi, %ecx
	mov CBFS_HEADER_PTR, %edi
	mov CBFS_HEADER_ALIGN(%edi), %edi
	bswap %edi
	sub $1, %edi
	add %edi, %ecx
	not %edi
	and %edi, %ecx

	/* if oldaddr >= addr, leave */
	cmp %ebx, %ecx
	jbe out

	mov %ecx, %ebx

check_for_exit:
	/* look if we should exit: did we pass into the bootblock already? */
	mov CBFS_HEADER_PTR, %ecx
	mov CBFS_HEADER_BOOTBLOCKSIZE(%ecx), %ecx
	bswap %ecx
	not %ecx
	add $1, %ecx

	cmp %ecx, %ebx
	/* if bootblockstart >= addr (==we're still in the data area) , jump back */
	jbe walker

out:
	mov $0, %eax
	jmp *%esp


searchfile:
	/* if filemagic isn't found, move forward cbfs_header->align bytes */
	mov CBFS_HEADER_PTR, %edi
	mov CBFS_HEADER_ALIGN(%edi), %edi
	bswap %edi
	add %edi, %ebx
	jmp check_for_exit

filemagic:
	.ascii "LARCHIVE"