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
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
|
# write: like _write, but also support in-memory streams in addition to file
# descriptors.
#
# Our first dependency-injected and testable primitive. We can pass it either
# a file descriptor or an address to a stream. If a file descriptor is passed
# in, we _write to it using the right syscall. If a 'fake file descriptor' or
# stream is passed in, we append to the stream. This lets us redirect output
# in tests and check it later.
#
# We assume our data segment will never begin at an address shorter than
# 0x08000000, so any smaller arguments are assumed to be real file descriptors.
#
# A stream looks like this:
# read: int # index at which to read next
# write: int # index at which writes go
# data: (array byte) # prefixed by size as usual
== code
# instruction effective address register displacement immediate
# . op subop mod rm32 base index scale r32
# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes
# TODO: come up with a way to signal when a write to disk fails
write: # f: fd or (addr stream byte), s: (addr array byte)
# . prologue
55/push-ebp
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# if (f < 0x08000000) _write(f, s) and return # f can't be a user-mode address, so treat it as a kernel file descriptor
81 7/subop/compare 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 0x08000000/imm32 # compare *(ebp+8)
73/jump-if-addr>= $write:fake/disp8
# . . push args
ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12)
ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8)
# . . call
e8/call _write/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
eb/jump $write:end/disp8
$write:fake:
# otherwise, treat 'f' as a stream to append to
# . save registers
50/push-eax
51/push-ecx
52/push-edx
53/push-ebx
# ecx = f
8b/copy 1/mod/*+disp8 5/rm32/ebp . . 1/r32/ecx 8/disp8 . # copy *(ebp+8) to ecx
# edx = f->write
8b/copy 0/mod/indirect 1/rm32/ecx . . . 2/r32/edx . . # copy *ecx to edx
# ebx = f->size
8b/copy 1/mod/*+disp8 1/rm32/ecx . . . 3/r32/ebx 8/disp8 . # copy *(ecx+8) to ebx
# eax = _append-3(&f->data[f->write], &f->data[f->size], s)
# . . push s
ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12)
# . . push &f->data[f->size]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ecx 3/index/ebx . 3/r32/ebx 0xc/disp8 . # copy ecx+ebx+12 to ebx
53/push-ebx
# . . push &f->data[f->write]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ecx 2/index/edx . 3/r32/ebx 0xc/disp8 . # copy ecx+edx+12 to ebx
53/push-ebx
# . . call
e8/call _append-3/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
# f->write += eax
01/add 0/mod/indirect 1/rm32/ecx . . . 0/r32/eax . . # add eax to *ecx
# . restore registers
5b/pop-to-ebx
5a/pop-to-edx
59/pop-to-ecx
58/pop-to-eax
$write:end:
# . epilogue
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
5d/pop-to-ebp
c3/return
test-write-single:
# clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# write(_test-stream, "Ab")
# . . push args
68/push "Ab"/imm32
68/push _test-stream/imm32
# . . call
e8/call write/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
# check-ints-equal(*_test-stream->data, 41/A 62/b 00 00, msg)
# . . push args
68/push "F - test-write-single"/imm32
68/push 0x006241/imm32/Ab
# . . push *_test-stream->data
b8/copy-to-eax _test-stream/imm32
ff 6/subop/push 1/mod/*+disp8 0/rm32/eax . . . . 0xc/disp8 . # push *(eax+12)
# . . call
e8/call check-ints-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
# end
c3/return
test-write-appends:
# clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# write(_test-stream, "C")
# . . push args
68/push "C"/imm32
68/push _test-stream/imm32
# . . call
e8/call write/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
# write(_test-stream, "D")
# . . push args
68/push "D"/imm32
68/push _test-stream/imm32
# . . call
e8/call write/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
# check-ints-equal(*_test-stream->data, 43/C 44/D 00 00, msg)
# . . push args
68/push "F - test-write-appends"/imm32
68/push 0x00004443/imm32/C-D
# . . push *_test-stream->data
b8/copy-to-eax _test-stream/imm32
ff 6/subop/push 1/mod/*+disp8 0/rm32/eax . . . . 0xc/disp8 . # push *(eax+12)
# . . call
e8/call check-ints-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
# end
c3/return
== data
_test-stream: # (stream byte)
# current write index
0/imm32
# current read index
0/imm32
# size
0x10/imm32
# data (2 lines x 8 bytes/line)
00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
# . . vim:nowrap:textwidth=0
|