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
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
|
# read-byte-buffered: one higher-level abstraction atop 'read'.
#
# There are many situations where 'read' is a lot to manage, and we need
# to abstract some details away. One of them is when we want to read a file
# character by character. In this situation we follow C's FILE data structure,
# which manages the underlying file descriptor together with the buffer it
# reads into. We call our version 'buffered-file'. Should be useful with other
# primitives as well, in later layers.
== data
# The buffered file for standard input. Also illustrates the layout for
# buffered-file: a pointer to the backing store, followed by a 'buffer' stream
Stdin:
# file descriptor or (address stream)
0/imm32 # standard input
Stdin->buffer:
# inlined fields for a stream
# current write index
0/imm32
# current read index
0/imm32
# length
8/imm32
# data
00 00 00 00 00 00 00 00 # 8 bytes
# TODO: 8 bytes is too small. We'll need to grow the buffer for efficiency. But
# I don't want to type in 1024 bytes here.
== 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
# return next byte value in eax, with top 3 bytes cleared.
# On reaching end of file, return 0xffffffff (Eof).
read-byte-buffered: # f : (address buffered-file) -> byte-or-Eof/eax
# . prologue
55/push-ebp
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# . save registers
51/push-ecx
56/push-esi
# esi = f
8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 8/disp8 . # copy *(ebp+8) to esi
# ecx = f->read
8b/copy 1/mod/*+disp8 6/rm32/esi . . . 1/r32/ecx 8/disp8 . # copy *(esi+8) to ecx
# if (f->read >= f->write) populate stream from file
3b/compare 1/mod/*+disp8 6/rm32/esi . . . 1/r32/ecx 4/disp8 . # compare ecx with *(esi+4)
7c/jump-if-lesser $read-byte-buffered:from-stream/disp8
# . clear-stream(stream = f+4)
# . . push args
8d/copy-address 1/mod/*+disp8 6/rm32/esi . . . 0/r32/eax 4/disp8 . # copy esi+4 to eax
50/push-eax
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# . f->read must now be 0; update its cache at ecx
31/xor 3/mod/direct 1/rm32/ecx . . . 1/r32/ecx . . # clear ecx
# . eax = read(f->fd, stream = f+4)
# . . push args
50/push-eax
ff 6/subop/push 0/mod/indirect 6/rm32/esi . . . . . . # push *esi
# . . call
e8/call read/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
# if (eax == 0) return 0xffffffff
3d/compare-eax-and 0/imm32
75/jump-if-not-equal $read-byte-buffered:from-stream/disp8
b8/copy-to-eax 0xffffffff/imm32/Eof
eb/jump $read-byte-buffered:end/disp8
$read-byte-buffered:from-stream:
# read byte from stream
# AL = f->data[f->read]
31/xor 3/mod/direct 0/rm32/eax . . . 0/r32/eax . . # clear eax
8a/copy-byte 1/mod/*+disp8 4/rm32/sib 6/base/esi 1/index/ecx . 0/r32/AL 0x10/disp8 . # copy byte at *(esi+ecx+16) to AL
# ++f->read
ff 0/subop/increment 1/mod/*+disp8 6/rm32/esi . . . . 8/disp8 . # increment *(esi+8)
$read-byte-buffered:end:
# . restore registers
5e/pop-to-esi
59/pop-to-ecx
# . epilogue
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
5d/pop-to-ebp
c3/return
# - tests
test-read-byte-buffered-single:
# - check that read-byte-buffered returns first byte of 'file'
# setup
# . 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
# . clear-stream(_test-buffered-file->buffer)
# . . push args
68/push _test-buffered-file->buffer/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
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# check-ints-equal(eax, 'A', msg)
# . . push args
68/push "F - test-read-byte-buffered-single"/imm32
68/push 0x41/imm32
50/push-eax
# . . 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-read-byte-buffered-multiple:
# - call read-byte-buffered twice, check that second call returns second byte
# setup
# . 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
# . clear-stream(_test-buffered-file->buffer)
# . . push args
68/push _test-buffered-file->buffer/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
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# check-ints-equal(eax, 'b', msg)
# . . push args
68/push "F - test-read-byte-buffered-multiple"/imm32
68/push 0x62/imm32
50/push-eax
# . . 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-read-byte-buffered-end-of-file:
# - call read-byte-buffered on an empty 'file', check that it returns Eof
# setup
# . 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
# . clear-stream(_test-buffered-file->buffer)
# . . push args
68/push _test-buffered-file->buffer/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# check-ints-equal(eax, 0xffffffff, msg)
# . . push args
68/push "F - test-read-byte-buffered-end-of-file"/imm32
68/push 0xffffffff/imm32/Eof
50/push-eax
# . . 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-read-byte-buffered-refills-buffer:
# - consume buffered-file's buffer, check that next read-byte-buffered still works
# setup
# . 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
# . clear-stream(_test-buffered-file->buffer)
# . . push args
68/push _test-buffered-file->buffer/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, "Abcdefgh")
# . . push args
68/push "Abcdefgh"/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
# pretend buffer is full
# . _test-buffered-file->read = 6 # >= _test-buffered-file->length
b8/copy-to-eax _test-buffered-file/imm32
c7 0/subop/copy 1/mod/*+disp8 0/rm32/eax . . . . 8/disp8 6/imm32 # copy to *(eax+8)
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# check-ints-equal(eax, 'A', msg)
# . . push args
68/push "F - test-read-byte-buffered-refills-buffer"/imm32
68/push 0x41/imm32
50/push-eax
# . . 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
# a test buffered file for _test-stream
_test-buffered-file:
# file descriptor or (address stream)
_test-stream/imm32
_test-buffered-file->buffer:
# current write index
0/imm32
# current read index
0/imm32
# length
6/imm32
# data
00 00 00 00 00 00 # 6 bytes
_test-input-stream:
# current write index
0/imm32
# current read index
0/imm32
# length
0x100/imm32 # 256 bytes
# data (16 lines x 16 bytes/line)
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
# a test buffered file for _test-input-stream
_test-input-buffered-file:
# file descriptor or (address stream)
_test-input-stream/imm32
_test-input-buffered-file->buffer:
# current write index
0/imm32
# current read index
0/imm32
# length
6/imm32
# data
00 00 00 00 00 00 # 6 bytes
# . . vim:nowrap:textwidth=0
|