CircuitPython

Source code browser

  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
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2014 Damien P. George
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <stdint.h>
#include <stdio.h>
#include <assert.h>
#include <string.h>

#include "py/mpconfig.h"

// wrapper around everything in this file
#if MICROPY_EMIT_X86

#include "py/asmx86.h"

/* all offsets are measured in multiples of 4 bytes */
#define WORD_SIZE                (4)

#define OPCODE_NOP               (0x90)
#define OPCODE_PUSH_R32          (0x50)
//#define OPCODE_PUSH_I32          (0x68)
//#define OPCODE_PUSH_M32          (0xff) /* /6 */
#define OPCODE_POP_R32           (0x58)
#define OPCODE_RET               (0xc3)
//#define OPCODE_MOV_I8_TO_R8      (0xb0) /* +rb */
#define OPCODE_MOV_I32_TO_R32    (0xb8)
//#define OPCODE_MOV_I32_TO_RM32   (0xc7)
#define OPCODE_MOV_R8_TO_RM8     (0x88) /* /r */
#define OPCODE_MOV_R32_TO_RM32   (0x89) /* /r */
#define OPCODE_MOV_RM32_TO_R32   (0x8b) /* /r */
#define OPCODE_MOVZX_RM8_TO_R32  (0xb6) /* 0x0f 0xb6/r */
#define OPCODE_MOVZX_RM16_TO_R32 (0xb7) /* 0x0f 0xb7/r */
#define OPCODE_LEA_MEM_TO_R32    (0x8d) /* /r */
#define OPCODE_AND_R32_TO_RM32   (0x21) /* /r */
#define OPCODE_OR_R32_TO_RM32    (0x09) /* /r */
#define OPCODE_XOR_R32_TO_RM32   (0x31) /* /r */
#define OPCODE_ADD_R32_TO_RM32   (0x01)
#define OPCODE_ADD_I32_TO_RM32   (0x81) /* /0 */
#define OPCODE_ADD_I8_TO_RM32    (0x83) /* /0 */
#define OPCODE_SUB_R32_FROM_RM32 (0x29)
#define OPCODE_SUB_I32_FROM_RM32 (0x81) /* /5 */
#define OPCODE_SUB_I8_FROM_RM32  (0x83) /* /5 */
//#define OPCODE_SHL_RM32_BY_I8    (0xc1) /* /4 */
//#define OPCODE_SHR_RM32_BY_I8    (0xc1) /* /5 */
//#define OPCODE_SAR_RM32_BY_I8    (0xc1) /* /7 */
#define OPCODE_SHL_RM32_CL       (0xd3) /* /4 */
#define OPCODE_SAR_RM32_CL       (0xd3) /* /7 */
//#define OPCODE_CMP_I32_WITH_RM32 (0x81) /* /7 */
//#define OPCODE_CMP_I8_WITH_RM32  (0x83) /* /7 */
#define OPCODE_CMP_R32_WITH_RM32 (0x39)
//#define OPCODE_CMP_RM32_WITH_R32 (0x3b)
#define OPCODE_TEST_R8_WITH_RM8  (0x84) /* /r */
#define OPCODE_JMP_REL8          (0xeb)
#define OPCODE_JMP_REL32         (0xe9)
#define OPCODE_JCC_REL8          (0x70) /* | jcc type */
#define OPCODE_JCC_REL32_A       (0x0f)
#define OPCODE_JCC_REL32_B       (0x80) /* | jcc type */
#define OPCODE_SETCC_RM8_A       (0x0f)
#define OPCODE_SETCC_RM8_B       (0x90) /* | jcc type, /0 */
#define OPCODE_CALL_REL32        (0xe8)
#define OPCODE_CALL_RM32         (0xff) /* /2 */
#define OPCODE_LEAVE             (0xc9)

#define MODRM_R32(x)    ((x) << 3)
#define MODRM_RM_DISP0  (0x00)
#define MODRM_RM_DISP8  (0x40)
#define MODRM_RM_DISP32 (0x80)
#define MODRM_RM_REG    (0xc0)
#define MODRM_RM_R32(x) (x)

#define OP_SIZE_PREFIX (0x66)

#define IMM32_L0(x) ((x) & 0xff)
#define IMM32_L1(x) (((x) >> 8) & 0xff)
#define IMM32_L2(x) (((x) >> 16) & 0xff)
#define IMM32_L3(x) (((x) >> 24) & 0xff)

#define SIGNED_FIT8(x) (((x) & 0xffffff80) == 0) || (((x) & 0xffffff80) == 0xffffff80)

STATIC void asm_x86_write_byte_1(asm_x86_t *as, byte b1) {
    byte* c = mp_asm_base_get_cur_to_write_bytes(&as->base, 1);
    if (c != NULL) {
        c[0] = b1;
    }
}

STATIC void asm_x86_write_byte_2(asm_x86_t *as, byte b1, byte b2) {
    byte* c = mp_asm_base_get_cur_to_write_bytes(&as->base, 2);
    if (c != NULL) {
        c[0] = b1;
        c[1] = b2;
    }
}

STATIC void asm_x86_write_byte_3(asm_x86_t *as, byte b1, byte b2, byte b3) {
    byte* c = mp_asm_base_get_cur_to_write_bytes(&as->base, 3);
    if (c != NULL) {
        c[0] = b1;
        c[1] = b2;
        c[2] = b3;
    }
}

STATIC void asm_x86_write_word32(asm_x86_t *as, int w32) {
    byte* c = mp_asm_base_get_cur_to_write_bytes(&as->base, 4);
    if (c != NULL) {
        c[0] = IMM32_L0(w32);
        c[1] = IMM32_L1(w32);
        c[2] = IMM32_L2(w32);
        c[3] = IMM32_L3(w32);
    }
}

STATIC void asm_x86_write_r32_disp(asm_x86_t *as, int r32, int disp_r32, int disp_offset) {
    assert(disp_r32 != ASM_X86_REG_ESP);

    if (disp_offset == 0 && disp_r32 != ASM_X86_REG_EBP) {
        asm_x86_write_byte_1(as, MODRM_R32(r32) | MODRM_RM_DISP0 | MODRM_RM_R32(disp_r32));
    } else if (SIGNED_FIT8(disp_offset)) {
        asm_x86_write_byte_2(as, MODRM_R32(r32) | MODRM_RM_DISP8 | MODRM_RM_R32(disp_r32), IMM32_L0(disp_offset));
    } else {
        asm_x86_write_byte_1(as, MODRM_R32(r32) | MODRM_RM_DISP32 | MODRM_RM_R32(disp_r32));
        asm_x86_write_word32(as, disp_offset);
    }
}

STATIC void asm_x86_generic_r32_r32(asm_x86_t *as, int dest_r32, int src_r32, int op) {
    asm_x86_write_byte_2(as, op, MODRM_R32(src_r32) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
}

STATIC void asm_x86_nop(asm_x86_t *as) {
    asm_x86_write_byte_1(as, OPCODE_NOP);
}

STATIC void asm_x86_push_r32(asm_x86_t *as, int src_r32) {
    asm_x86_write_byte_1(as, OPCODE_PUSH_R32 | src_r32);
}

#if 0
void asm_x86_push_i32(asm_x86_t *as, int src_i32) {
    asm_x86_write_byte_1(as, OPCODE_PUSH_I32);
    asm_x86_write_word32(as, src_i32);
}

void asm_x86_push_disp(asm_x86_t *as, int src_r32, int src_offset) {
    asm_x86_write_byte_1(as, OPCODE_PUSH_M32);
    asm_x86_write_r32_disp(as, 6, src_r32, src_offset);
}
#endif

STATIC void asm_x86_pop_r32(asm_x86_t *as, int dest_r32) {
    asm_x86_write_byte_1(as, OPCODE_POP_R32 | dest_r32);
}

STATIC void asm_x86_ret(asm_x86_t *as) {
    asm_x86_write_byte_1(as, OPCODE_RET);
}

void asm_x86_mov_r32_r32(asm_x86_t *as, int dest_r32, int src_r32) {
    asm_x86_generic_r32_r32(as, dest_r32, src_r32, OPCODE_MOV_R32_TO_RM32);
}

void asm_x86_mov_r8_to_mem8(asm_x86_t *as, int src_r32, int dest_r32, int dest_disp) {
    asm_x86_write_byte_1(as, OPCODE_MOV_R8_TO_RM8);
    asm_x86_write_r32_disp(as, src_r32, dest_r32, dest_disp);
}

void asm_x86_mov_r16_to_mem16(asm_x86_t *as, int src_r32, int dest_r32, int dest_disp) {
    asm_x86_write_byte_2(as, OP_SIZE_PREFIX, OPCODE_MOV_R32_TO_RM32);
    asm_x86_write_r32_disp(as, src_r32, dest_r32, dest_disp);
}

void asm_x86_mov_r32_to_mem32(asm_x86_t *as, int src_r32, int dest_r32, int dest_disp) {
    asm_x86_write_byte_1(as, OPCODE_MOV_R32_TO_RM32);
    asm_x86_write_r32_disp(as, src_r32, dest_r32, dest_disp);
}

void asm_x86_mov_mem8_to_r32zx(asm_x86_t *as, int src_r32, int src_disp, int dest_r32) {
    asm_x86_write_byte_2(as, 0x0f, OPCODE_MOVZX_RM8_TO_R32);
    asm_x86_write_r32_disp(as, dest_r32, src_r32, src_disp);
}

void asm_x86_mov_mem16_to_r32zx(asm_x86_t *as, int src_r32, int src_disp, int dest_r32) {
    asm_x86_write_byte_2(as, 0x0f, OPCODE_MOVZX_RM16_TO_R32);
    asm_x86_write_r32_disp(as, dest_r32, src_r32, src_disp);
}

void asm_x86_mov_mem32_to_r32(asm_x86_t *as, int src_r32, int src_disp, int dest_r32) {
    asm_x86_write_byte_1(as, OPCODE_MOV_RM32_TO_R32);
    asm_x86_write_r32_disp(as, dest_r32, src_r32, src_disp);
}

STATIC void asm_x86_lea_disp_to_r32(asm_x86_t *as, int src_r32, int src_disp, int dest_r32) {
    asm_x86_write_byte_1(as, OPCODE_LEA_MEM_TO_R32);
    asm_x86_write_r32_disp(as, dest_r32, src_r32, src_disp);
}

#if 0
void asm_x86_mov_i8_to_r8(asm_x86_t *as, int src_i8, int dest_r32) {
    asm_x86_write_byte_2(as, OPCODE_MOV_I8_TO_R8 | dest_r32, src_i8);
}
#endif

void asm_x86_mov_i32_to_r32(asm_x86_t *as, int32_t src_i32, int dest_r32) {
    asm_x86_write_byte_1(as, OPCODE_MOV_I32_TO_R32 | dest_r32);
    asm_x86_write_word32(as, src_i32);
}

// src_i32 is stored as a full word in the code, and aligned to machine-word boundary
void asm_x86_mov_i32_to_r32_aligned(asm_x86_t *as, int32_t src_i32, int dest_r32) {
    // mov instruction uses 1 byte for the instruction, before the i32
    while (((as->base.code_offset + 1) & (WORD_SIZE - 1)) != 0) {
        asm_x86_nop(as);
    }
    asm_x86_mov_i32_to_r32(as, src_i32, dest_r32);
}

void asm_x86_and_r32_r32(asm_x86_t *as, int dest_r32, int src_r32) {
    asm_x86_generic_r32_r32(as, dest_r32, src_r32, OPCODE_AND_R32_TO_RM32);
}

void asm_x86_or_r32_r32(asm_x86_t *as, int dest_r32, int src_r32) {
    asm_x86_generic_r32_r32(as, dest_r32, src_r32, OPCODE_OR_R32_TO_RM32);
}

void asm_x86_xor_r32_r32(asm_x86_t *as, int dest_r32, int src_r32) {
    asm_x86_generic_r32_r32(as, dest_r32, src_r32, OPCODE_XOR_R32_TO_RM32);
}

void asm_x86_shl_r32_cl(asm_x86_t* as, int dest_r32) {
    asm_x86_generic_r32_r32(as, dest_r32, 4, OPCODE_SHL_RM32_CL);
}

void asm_x86_sar_r32_cl(asm_x86_t* as, int dest_r32) {
    asm_x86_generic_r32_r32(as, dest_r32, 7, OPCODE_SAR_RM32_CL);
}

void asm_x86_add_r32_r32(asm_x86_t *as, int dest_r32, int src_r32) {
    asm_x86_generic_r32_r32(as, dest_r32, src_r32, OPCODE_ADD_R32_TO_RM32);
}

STATIC void asm_x86_add_i32_to_r32(asm_x86_t *as, int src_i32, int dest_r32) {
    if (SIGNED_FIT8(src_i32)) {
        asm_x86_write_byte_2(as, OPCODE_ADD_I8_TO_RM32, MODRM_R32(0) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
        asm_x86_write_byte_1(as, src_i32 & 0xff);
    } else {
        asm_x86_write_byte_2(as, OPCODE_ADD_I32_TO_RM32, MODRM_R32(0) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
        asm_x86_write_word32(as, src_i32);
    }
}

void asm_x86_sub_r32_r32(asm_x86_t *as, int dest_r32, int src_r32) {
    asm_x86_generic_r32_r32(as, dest_r32, src_r32, OPCODE_SUB_R32_FROM_RM32);
}

STATIC void asm_x86_sub_r32_i32(asm_x86_t *as, int dest_r32, int src_i32) {
    if (SIGNED_FIT8(src_i32)) {
        // defaults to 32 bit operation
        asm_x86_write_byte_2(as, OPCODE_SUB_I8_FROM_RM32, MODRM_R32(5) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
        asm_x86_write_byte_1(as, src_i32 & 0xff);
    } else {
        // defaults to 32 bit operation
        asm_x86_write_byte_2(as, OPCODE_SUB_I32_FROM_RM32, MODRM_R32(5) | MODRM_RM_REG | MODRM_RM_R32(dest_r32));
        asm_x86_write_word32(as, src_i32);
    }
}

void asm_x86_mul_r32_r32(asm_x86_t *as, int dest_r32, int src_r32) {
    // imul reg32, reg/mem32 -- 0x0f 0xaf /r
    asm_x86_write_byte_3(as, 0x0f, 0xaf, MODRM_R32(dest_r32) | MODRM_RM_REG | MODRM_RM_R32(src_r32));
}

#if 0
/* shifts not tested */
void asm_x86_shl_r32_by_imm(asm_x86_t *as, int r32, int imm) {
    asm_x86_write_byte_2(as, OPCODE_SHL_RM32_BY_I8, MODRM_R32(4) | MODRM_RM_REG | MODRM_RM_R32(r32));
    asm_x86_write_byte_1(as, imm);
}

void asm_x86_shr_r32_by_imm(asm_x86_t *as, int r32, int imm) {
    asm_x86_write_byte_2(as, OPCODE_SHR_RM32_BY_I8, MODRM_R32(5) | MODRM_RM_REG | MODRM_RM_R32(r32));
    asm_x86_write_byte_1(as, imm);
}

void asm_x86_sar_r32_by_imm(asm_x86_t *as, int r32, int imm) {
    asm_x86_write_byte_2(as, OPCODE_SAR_RM32_BY_I8, MODRM_R32(7) | MODRM_RM_REG | MODRM_RM_R32(r32));
    asm_x86_write_byte_1(as, imm);
}
#endif

void asm_x86_cmp_r32_with_r32(asm_x86_t *as, int src_r32_a, int src_r32_b) {
    asm_x86_write_byte_2(as, OPCODE_CMP_R32_WITH_RM32, MODRM_R32(src_r32_a) | MODRM_RM_REG | MODRM_RM_R32(src_r32_b));
}

#if 0
void asm_x86_cmp_i32_with_r32(asm_x86_t *as, int src_i32, int src_r32) {
    if (SIGNED_FIT8(src_i32)) {
        asm_x86_write_byte_2(as, OPCODE_CMP_I8_WITH_RM32, MODRM_R32(7) | MODRM_RM_REG | MODRM_RM_R32(src_r32));
        asm_x86_write_byte_1(as, src_i32 & 0xff);
    } else {
        asm_x86_write_byte_2(as, OPCODE_CMP_I32_WITH_RM32, MODRM_R32(7) | MODRM_RM_REG | MODRM_RM_R32(src_r32));
        asm_x86_write_word32(as, src_i32);
    }
}
#endif

void asm_x86_test_r8_with_r8(asm_x86_t *as, int src_r32_a, int src_r32_b) {
    // TODO implement for other registers
    assert(src_r32_a == ASM_X86_REG_EAX);
    assert(src_r32_b == ASM_X86_REG_EAX);
    asm_x86_write_byte_2(as, OPCODE_TEST_R8_WITH_RM8, MODRM_R32(src_r32_a) | MODRM_RM_REG | MODRM_RM_R32(src_r32_b));
}

void asm_x86_setcc_r8(asm_x86_t *as, mp_uint_t jcc_type, int dest_r8) {
    asm_x86_write_byte_3(as, OPCODE_SETCC_RM8_A, OPCODE_SETCC_RM8_B | jcc_type, MODRM_R32(0) | MODRM_RM_REG | MODRM_RM_R32(dest_r8));
}

STATIC mp_uint_t get_label_dest(asm_x86_t *as, mp_uint_t label) {
    assert(label < as->base.max_num_labels);
    return as->base.label_offsets[label];
}

void asm_x86_jmp_label(asm_x86_t *as, mp_uint_t label) {
    mp_uint_t dest = get_label_dest(as, label);
    mp_int_t rel = dest - as->base.code_offset;
    if (dest != (mp_uint_t)-1 && rel < 0) {
        // is a backwards jump, so we know the size of the jump on the first pass
        // calculate rel assuming 8 bit relative jump
        rel -= 2;
        if (SIGNED_FIT8(rel)) {
            asm_x86_write_byte_2(as, OPCODE_JMP_REL8, rel & 0xff);
        } else {
            rel += 2;
            goto large_jump;
        }
    } else {
        // is a forwards jump, so need to assume it's large
        large_jump:
        rel -= 5;
        asm_x86_write_byte_1(as, OPCODE_JMP_REL32);
        asm_x86_write_word32(as, rel);
    }
}

void asm_x86_jcc_label(asm_x86_t *as, mp_uint_t jcc_type, mp_uint_t label) {
    mp_uint_t dest = get_label_dest(as, label);
    mp_int_t rel = dest - as->base.code_offset;
    if (dest != (mp_uint_t)-1 && rel < 0) {
        // is a backwards jump, so we know the size of the jump on the first pass
        // calculate rel assuming 8 bit relative jump
        rel -= 2;
        if (SIGNED_FIT8(rel)) {
            asm_x86_write_byte_2(as, OPCODE_JCC_REL8 | jcc_type, rel & 0xff);
        } else {
            rel += 2;
            goto large_jump;
        }
    } else {
        // is a forwards jump, so need to assume it's large
        large_jump:
        rel -= 6;
        asm_x86_write_byte_2(as, OPCODE_JCC_REL32_A, OPCODE_JCC_REL32_B | jcc_type);
        asm_x86_write_word32(as, rel);
    }
}

void asm_x86_entry(asm_x86_t *as, int num_locals) {
    assert(num_locals >= 0);
    asm_x86_push_r32(as, ASM_X86_REG_EBP);
    asm_x86_mov_r32_r32(as, ASM_X86_REG_EBP, ASM_X86_REG_ESP);
    if (num_locals > 0) {
        asm_x86_sub_r32_i32(as, ASM_X86_REG_ESP, num_locals * WORD_SIZE);
    }
    asm_x86_push_r32(as, ASM_X86_REG_EBX);
    asm_x86_push_r32(as, ASM_X86_REG_ESI);
    asm_x86_push_r32(as, ASM_X86_REG_EDI);
    // TODO align stack on 16-byte boundary
    as->num_locals = num_locals;
}

void asm_x86_exit(asm_x86_t *as) {
    asm_x86_pop_r32(as, ASM_X86_REG_EDI);
    asm_x86_pop_r32(as, ASM_X86_REG_ESI);
    asm_x86_pop_r32(as, ASM_X86_REG_EBX);
    asm_x86_write_byte_1(as, OPCODE_LEAVE);
    asm_x86_ret(as);
}

#if 0
void asm_x86_push_arg(asm_x86_t *as, int src_arg_num) {
    asm_x86_push_disp(as, ASM_X86_REG_EBP, 2 * WORD_SIZE + src_arg_num * WORD_SIZE);
}
#endif

void asm_x86_mov_arg_to_r32(asm_x86_t *as, int src_arg_num, int dest_r32) {
    asm_x86_mov_mem32_to_r32(as, ASM_X86_REG_EBP, 2 * WORD_SIZE + src_arg_num * WORD_SIZE, dest_r32);
}

#if 0
void asm_x86_mov_r32_to_arg(asm_x86_t *as, int src_r32, int dest_arg_num) {
    asm_x86_mov_r32_to_mem32(as, src_r32, ASM_X86_REG_EBP, 2 * WORD_SIZE + dest_arg_num * WORD_SIZE);
}
#endif

// locals:
//  - stored on the stack in ascending order
//  - numbered 0 through as->num_locals-1
//  - EBP points above the last local
//
//                          | EBP
//                          v
//  l0  l1  l2  ...  l(n-1)
//  ^                ^
//  | low address    | high address in RAM
//
STATIC int asm_x86_local_offset_from_ebp(asm_x86_t *as, int local_num) {
    return (-as->num_locals + local_num) * WORD_SIZE;
}

void asm_x86_mov_local_to_r32(asm_x86_t *as, int src_local_num, int dest_r32) {
    asm_x86_mov_mem32_to_r32(as, ASM_X86_REG_EBP, asm_x86_local_offset_from_ebp(as, src_local_num), dest_r32);
}

void asm_x86_mov_r32_to_local(asm_x86_t *as, int src_r32, int dest_local_num) {
    asm_x86_mov_r32_to_mem32(as, src_r32, ASM_X86_REG_EBP, asm_x86_local_offset_from_ebp(as, dest_local_num));
}

void asm_x86_mov_local_addr_to_r32(asm_x86_t *as, int local_num, int dest_r32) {
    int offset = asm_x86_local_offset_from_ebp(as, local_num);
    if (offset == 0) {
        asm_x86_mov_r32_r32(as, dest_r32, ASM_X86_REG_EBP);
    } else {
        asm_x86_lea_disp_to_r32(as, ASM_X86_REG_EBP, offset, dest_r32);
    }
}

#if 0
void asm_x86_push_local(asm_x86_t *as, int local_num) {
    asm_x86_push_disp(as, ASM_X86_REG_EBP, asm_x86_local_offset_from_ebp(as, local_num));
}

void asm_x86_push_local_addr(asm_x86_t *as, int local_num, int temp_r32)
{
    asm_x86_mov_r32_r32(as, temp_r32, ASM_X86_REG_EBP);
    asm_x86_add_i32_to_r32(as, asm_x86_local_offset_from_ebp(as, local_num), temp_r32);
    asm_x86_push_r32(as, temp_r32);
}
#endif

void asm_x86_call_ind(asm_x86_t *as, void *ptr, mp_uint_t n_args, int temp_r32) {
    // TODO align stack on 16-byte boundary before the call
    assert(n_args <= 5);
    if (n_args > 4) {
        asm_x86_push_r32(as, ASM_X86_REG_ARG_5);
    }
    if (n_args > 3) {
        asm_x86_push_r32(as, ASM_X86_REG_ARG_4);
    }
    if (n_args > 2) {
        asm_x86_push_r32(as, ASM_X86_REG_ARG_3);
    }
    if (n_args > 1) {
        asm_x86_push_r32(as, ASM_X86_REG_ARG_2);
    }
    if (n_args > 0) {
        asm_x86_push_r32(as, ASM_X86_REG_ARG_1);
    }
#ifdef __LP64__
    // We wouldn't run x86 code on an x64 machine.  This is here to enable
    // testing of the x86 emitter only.
    asm_x86_mov_i32_to_r32(as, (int32_t)(int64_t)ptr, temp_r32);
#else
    // If we get here, sizeof(int) == sizeof(void*).
    asm_x86_mov_i32_to_r32(as, (int32_t)ptr, temp_r32);
#endif
    asm_x86_write_byte_2(as, OPCODE_CALL_RM32, MODRM_R32(2) | MODRM_RM_REG | MODRM_RM_R32(temp_r32));
    // this reduces code size by 2 bytes per call, but doesn't seem to speed it up at all
    /*
    asm_x86_write_byte_1(as, OPCODE_CALL_REL32);
    asm_x86_write_word32(as, ptr - (void*)(as->code_base + as->base.code_offset + 4));
    */

    // the caller must clean up the stack
    if (n_args > 0) {
        asm_x86_add_i32_to_r32(as, WORD_SIZE * n_args, ASM_X86_REG_ESP);
    }
}

#endif // MICROPY_EMIT_X86