1 # Helpers to compute widths of SubX arguments based on their metadata.
  2 #   /imm8 => 1 byte,
  3 #   /disp32 => 4 bytes,
  4 #   and so on.
  5 
  6 == code
  7 #   instruction                     effective address                                                   register    displacement    immediate
  8 # . op          subop               mod             rm32          base        index         scale       r32
  9 # . 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
 10 
 11 compute-width: # word: (addr array byte) -> eax: int
 12     # . prologue
 13     55/push-ebp
 14     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
 15     # . save registers
 16     51/push-ecx
 17     # eax = word
 18     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   8/disp8         .                 # copy *(ebp+8) to ecx
 19     # var ecx: (addr byte) = &word[word->size]
 20     8b/copy                         0/mod/indirect  0/rm32/eax    .           .             .           1/r32/ecx   .               .                 # copy *eax to ecx
 21     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    0/base/eax  1/index/ecx   .           1/r32/ecx   4/disp8         .                 # copy eax+ecx+4 to ecx
 22     # eax = word->data
 23     05/add-to-eax  4/imm32
 24     # var in/ecx: slice = {eax, ecx}
 25     51/push-ecx
 26     50/push-eax
 27     89/copy                         3/mod/direct    1/rm32/ecx    .           .             .           4/r32/esp   .               .                 # copy esp to ecx
 28     # return compute-width-of-slice(ecx)
 29     # . . push args
 30     51/push-ecx
 31     # . . call
 32     e8/call  compute-width-of-slice/disp32
 33     # . . discard args
 34     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
 35 $compute-width:end:
 36     # . reclaim locals
 37     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
 38     # . restore registers
 39     59/pop-to-ecx
 40     # . epilogue
 41     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
 42     5d/pop-to-ebp
 43     c3/return
 44 
 45 compute-width-of-slice: # s: (addr slice) -> eax: int
 46     # . prologue
 47     55/push-ebp
 48     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
 49     # . save registers
 50     51/push-ecx
 51     # ecx = s
 52     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           1/r32/ecx   8/disp8         .                 # copy *(ebp+8) to ecx
 53     # if (has-metadata?(word, "imm32")) return 4
 54     # . eax = has-metadata?(word, "imm32")
 55     # . . push args
 56     68/push  "imm32"/imm32
 57     51/push-ecx
 58     # . . call
 59     e8/call  has-metadata?/disp32
 60     # . . discard args
 61     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
 62     # . if (eax != false) return 4
 63     3d/compare-eax-and  0/imm32/false
 64     b8/copy-to-eax  4/imm32         # ZF is set, so we can overwrite eax now
 65     75/jump-if-!=  $compute-width-of-slice:end/disp8
 66     # if (has-metadata?(word, "disp32")) return 4
 67     # . eax = has-metadata?(word, "disp32")
 68     # . . push args
 69     68/push  "disp32"/imm32
 70     51/push-ecx
 71     # . . call
 72     e8/call  has-metadata?/disp32
 73     # . . discard args
 74     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
 75     # . if (eax != false) return 4
 76     3d/compare-eax-and  0/imm32/false
 77     b8/copy-to-eax  4/imm32         # ZF is set, so we can overwrite eax now
 78     75/jump-if-!=  $compute-width-of-slice:end/disp8
 79     # if (has-metadata?(word, "imm16")) return 2
 80     # . eax = has-metadata?(word, "imm16")
 81     # . . push args
 82     68/push  "imm16"/imm32
 83     51/push-ecx
 84     # . . call
 85     e8/call  has-metadata?/disp32
 86     # . . discard args
 87     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
 88     # . if (eax != false) return 2
 89     3d/compare-eax-and  0/imm32/false
 90     b8/copy-to-eax  2/imm32         # ZF is set, so we can overwrite eax now
 91     75/jump-if-!=  $compute-width-of-slice:end/disp8
 92     # if (has-metadata?(word, "disp16")) return 2
 93     # . eax = has-metadata?(word, "disp16")
 94     # . . push args
 95     68/push  "disp16"/imm32
 96     51/push-ecx
 97     # . . call
 98     e8/call  has-metadata?/disp32
 99     # . . discard args
100     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
101     # . if (eax != false) return 2
102     3d/compare-eax-and  0/imm32/false
103     b8/copy-to-eax  2/imm32         # ZF is set, so we can overwrite eax now
104     75/jump-if-!=  $compute-width-of-slice:end/disp8
105     # otherwise return 1
106     b8/copy-to-eax  1/imm32
107 $compute-width-of-slice:end:
108     # . restore registers
109     59/pop-to-ecx
110     # . epilogue
111     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
112     5d/pop-to-ebp
113     c3/return
114 
115 test-compute-width:
116     # . prologue
117     55/push-ebp
118     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
119 $test-compute-width:imm8:
120     # eax = compute-width("0x2/imm8")
121     # . . push args
122     68/push  "0x2/imm8"/imm32
123     # . . call
124     e8/call  compute-width/disp32
125     # . . discard args
126     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
127     # check-ints-equal(eax, 1, msg)
128     # . . push args
129     68/push  "F - test-compute-width: 0x2/imm8"/imm32
130     50/push-eax
131     68/push  1/imm32
132     # . . call
133     e8/call  check-ints-equal/disp32
134     # . . discard args
135     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
136 $test-compute-width:imm16:
137     # eax = compute-width("4/imm16")
138     # . . push args
139     68/push  "4/imm16"/imm32
140     # . . call
141     e8/call  compute-width/disp32
142     # . . discard args
143     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
144     # check-ints-equal(eax, 2, msg)
145     # . . push args
146     68/push  "F - test-compute-width: 4/imm16"/imm32
147     50/push-eax
148     68/push  2/imm32
149     # . . call
150     e8/call  check-ints-equal/disp32
151     # . . discard args
152     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
153 $test-compute-width:imm32:
154     # eax = compute-width("4/imm32")
155     # . . push args
156     68/push  "4/imm32"/imm32
157     # . . call
158     e8/call  compute-width/disp32
159     # . . discard args
160     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
161     # check-ints-equal(eax, 4, msg)
162     # . . push args
163     68/push  "F - test-compute-width: 4/imm32"/imm32
164     50/push-eax
165     68/push  4/imm32
166     # . . call
167     e8/call  check-ints-equal/disp32
168     # . . discard args
169     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
170 $test-compute-width:disp8:
171     # eax = compute-width("foo/disp8")
172     # . . push args
173     68/push  "foo/disp8"/imm32
174     # . . call
175     e8/call  compute-width/disp32
176     # . . discard args
177     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
178     # check-ints-equal(eax, 1, msg)
179     # . . push args
180     68/push  "F - test-compute-width: foo/disp8"/imm32
181     50/push-eax
182     68/push  1/imm32
183     # . . call
184     e8/call  check-ints-equal/disp32
185     # . . discard args
186     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
187 $test-compute-width:disp16:
188     # eax = compute-width("foo/disp16")
189     # . . push args
190     68/push  "foo/disp16"/imm32
191     # . . call
192     e8/call  compute-width/disp32
193     # . . discard args
194     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
195     # check-ints-equal(eax, 2, msg)
196     # . . push args
197     68/push  "F - test-compute-width: foo/disp16"/imm32
198     50/push-eax
199     68/push  2/imm32
200     # . . call
201     e8/call  check-ints-equal/disp32
202     # . . discard args
203     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
204 $test-compute-width:disp32:
205     # eax = compute-width("foo/disp32")
206     # . . push args
207     68/push  "foo/disp32"/imm32
208     # . . call
209     e8/call  compute-width/disp32
210     # . . discard args
211     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
212     # check-ints-equal(eax, 4, msg)
213     # . . push args
214     68/push  "F - test-compute-width: foo/disp32"/imm32
215     50/push-eax
216     68/push  4/imm32
217     # . . call
218     e8/call  check-ints-equal/disp32
219     # . . discard args
220     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
221 $test-compute-width:no-metadata:
222     # eax = compute-width("45")
223     # . . push args
224     68/push  "45"/imm32
225     # . . call
226     e8/call  compute-width/disp32
227     # . . discard args
228     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
229     # check-ints-equal(eax, 1, msg)
230     # . . push args
231     68/push  "F - test-compute-width: 45 (no metadata)"/imm32
232     50/push-eax
233     68/push  1/imm32
234     # . . call
235     e8/call  check-ints-equal/disp32
236     # . . discard args
237     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
238     # . epilogue
239     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
240     5d/pop-to-ebp
241     c3/return
242 
243 # . . vim:nowrap:textwidth=0