about summary refs log tree commit diff stats
path: root/subx/052kernel_string_equal.subx
blob: 341607b521274d796ea70224cf8e83f075f8223e (plain) (blame)
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
## Checking null-terminated ascii strings.
#
# By default we create strings with a 4-byte length prefix rather than a null suffix.
# However we still need null-prefixed strings when interacting with the Linux
# kernel in a few places. This layer implements a function for comparing
# a null-terminated 'kernel string' with a length-prefixed 'SubX string'.
#
# To run (from the subx directory):
#   $ subx translate 05[0-2]*.subx -o /tmp/tmp52
#   $ subx run /tmp/tmp52  # runs a series of tests
#   ......  # all tests pass
#
# (We can't yet run the tests when given a "test" commandline argument,
# because checking for it would require the function being tested! Breakage
# would cause tests to not run, rather than to fail as we'd like.)

== code
# instruction                     effective address                                                   operand     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

# main:
  e8/call  run-tests/disp32  # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'.
  # exit(Num-test-failures)
  8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           3/r32/EBX   Num-test-failures/disp32          # copy *Num-test-failures to EBX
  b8/copy-to-EAX  1/imm32
  cd/syscall  0x80/imm8

# compare a null-terminated ascii string with a more idiomatic length-prefixed byte array
# reason for the name: the only place we should have null-terminated ascii strings is from commandline args
kernel-string-equal:  # s : null-terminated ascii string, benchmark : length-prefixed ascii string -> EAX : boolean
  # prolog
  55/push-EBP
  89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
  # save registers
  51/push-ECX
  52/push-EDX
  53/push-EBX
  56/push-ESI
  57/push-EDI

  # pseudocode:
  #   initialize n = b.length
  #   initialize s1 = s
  #   initialize s2 = b.data
  #   i = 0
  #   for (i = 0; i < n; ++n)
  #     c1 = *s1
  #     c2 = *s2
  #     if c1 == 0
  #       return false
  #     if c1 != c2
  #       return false
  #   return *s1 == 0
  #
  # initialize s into EDI
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           7/r32/EDI   8/disp8         .                 # copy *(EBP+8) to EDI
  # initialize benchmark length n into EDX
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           2/r32/EDX   0xc/disp8       .                 # copy *(EBP+12) to EDX
  8b/copy                         0/mod/indirect  2/rm32/EDX    .           .             .           2/r32/EDX   .               .                 # copy *EDX to EDX
  # initialize benchmark data into ESI
  8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           6/r32/ESI   0xc/disp8       .                 # copy *(EBP+12) to ESI
  81          0/subop/add         3/mod/direct    6/rm32/ESI    .           .             .           .           .               4/imm32           # add to ESI
  # initialize loop counter i into ECX
  b9/copy-to-ECX  0/imm32/exit
  # while (i/ECX < n/EDX)
$kernel-string-equal:loop:
  39/compare                      3/mod/direct    1/rm32/ECX    .           .             .           2/r32/EDX   .               .                 # compare ECX with EDX
  74/jump-if-equal  $kernel-string-equal:break/disp8
    # c1/EAX, c2/EBX = *s, *benchmark
  b8/copy-to-EAX  0/imm32
  8a/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           0/r32/EAX   .               .                 # copy byte at *EDI to lower byte of EAX
  bb/copy-to-EBX  0/imm32
  8a/copy                         0/mod/indirect  6/rm32/ESI    .           .             .           3/r32/EBX   .               .                 # copy byte at *ESI to lower byte of EBX
    # if (c1 == 0) return false
  3d/compare-EAX  0/imm32
  74/jump-if-equal  $kernel-string-equal:false/disp8
    # if (c1 != c2) return false
  39/compare                      3/mod/direct    0/rm32/EAX    .           .             .           3/r32/EBX   .               .                 # compare EAX with EBX
  75/jump-if-not-equal  $kernel-string-equal:false/disp8
    # ++s1, ++s2, ++i
  41/inc-ECX
  46/inc-ESI
  47/inc-EDI
  # end while
  eb/jump  $kernel-string-equal:loop/disp8
$kernel-string-equal:break:
  # if (*s/EDI == 0) return true
  b8/copy-to-EAX  0/imm32
  8a/copy                         0/mod/indirect  7/rm32/EDI    .           .             .           0/r32/EAX   .               .                 # copy byte at *EDI to lower byte of EAX
  3d/compare-EAX  0/imm32
  75/jump-if-not-equal  $kernel-string-equal:false/disp8
$kernel-string-equal:true:
  b8/copy-to-EAX  1/imm32
  eb/jump  $kernel-string-equal:end/disp8
  # return false
$kernel-string-equal:false:
  b8/copy-to-EAX  0/imm32

$kernel-string-equal:end:
  # restore registers
  5f/pop-to-EDI
  5e/pop-to-ESI
  5b/pop-to-EBX
  5a/pop-to-EDX
  59/pop-to-ECX
  # epilog
  89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
  5d/pop-to-EBP
  c3/return

## tests

test-compare-null-kernel-string-with-empty-array:
  # EAX = kernel-string-equal(Null-kernel-string, "")
    # push args
  68/push  ""/imm32
  68/push  Null-kernel-string/imm32
    # call
  e8/call  kernel-string-equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # call check-ints-equal(EAX, 1, msg)
    # push args
  68/push  "F - test-compare-null-kernel-string-with-empty-array"/imm32
  68/push  1/imm32/true
  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
  c3/return

test-compare-null-kernel-string-with-non-empty-array:
  # EAX = kernel-string-equal(Null-kernel-string, "Abc")
    # push args
  68/push  "Abc"/imm32
  68/push  Null-kernel-string/imm32
    # call
  e8/call  kernel-string-equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # call check-ints-equal(EAX, 0, msg)
    # push args
  68/push  "F - test-compare-null-kernel-string-with-non-empty-array"/imm32
  68/push  0/imm32/false
  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
  c3/return

test-compare-kernel-string-with-equal-array:
  # EAX = kernel-string-equal(Abc-kernel-string, "Abc")
    # push args
  68/push  "Abc"/imm32
  68/push  Abc-kernel-string/imm32
    # call
  e8/call  kernel-string-equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # call check-ints-equal(EAX, 1, msg)
    # push args
  68/push  "F - test-compare-kernel-string-with-equal-array"/imm32
  68/push  1/imm32/true
  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
  c3/return

test-compare-kernel-string-with-inequal-array:
  # EAX = kernel-string-equal(Abc-kernel-string, "Adc")
    # push args
  68/push  "Adc"/imm32
  68/push  Abc-kernel-string/imm32
    # call
  e8/call  kernel-string-equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # call check-ints-equal(EAX, 0, msg)
    # push args
  68/push  "F - test-compare-kernel-string-with-equal-array"/imm32
  68/push  0/imm32/false
  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
  c3/return

test-compare-kernel-string-with-empty-array:
  # EAX = kernel-string-equal(Abc-kernel-string, "")
    # push args
  68/push  ""/imm32
  68/push  Abc-kernel-string/imm32
    # call
  e8/call  kernel-string-equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # call check-ints-equal(EAX, 0)
    # push args
  68/push  "F - test-compare-kernel-string-with-equal-array"/imm32
  68/push  0/imm32/false
  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
  c3/return

test-compare-kernel-string-with-shorter-array:
  # EAX = kernel-string-equal(Abc-kernel-string, "Ab")
    # push args
  68/push  "Ab"/imm32
  68/push  Abc-kernel-string/imm32
    # call
  e8/call  kernel-string-equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # call check-ints-equal(EAX, 0)
    # push args
  68/push  "F - test-compare-kernel-string-with-shorter-array"/imm32
  68/push  0/imm32/false
  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
  c3/return

test-compare-kernel-string-with-longer-array:
  # EAX = kernel-string-equal(Abc-kernel-string, "Abcd")
    # push args
  68/push  "Abcd"/imm32
  68/push  Abc-kernel-string/imm32
    # call
  e8/call  kernel-string-equal/disp32
    # discard args
  81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
  # call check-ints-equal(EAX, 0)
    # push args
  68/push  "F - test-compare-kernel-string-with-longer-array"/imm32
  68/push  0/imm32/false
  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
  c3/return

== data

Null-kernel-string:
  00/null
Abc-kernel-string:
  41/A 62/b 63/c 00/null

# vim:nowrap:textwidth=0