| 1 | /* (c) 2021 Aaron Taylor <ataylor at subgeniuskitty dot com> */ |
| 2 | /* See LICENSE.txt file for copyright and license details. */ |
| 3 | |
| 4 | /* -------------------------------------------------------------------------- */ |
| 5 | /* NED1 Simulator */ |
| 6 | /* -------------------------------------------------------------------------- */ |
| 7 | |
| 8 | // TODO: Make a bunch of functions private in this file. |
| 9 | #include <stdio.h> |
| 10 | #include <stdint.h> |
| 11 | #include <inttypes.h> |
| 12 | #include <stdlib.h> |
| 13 | #include <stdbool.h> |
| 14 | #include <unistd.h> |
| 15 | #include <fcntl.h> |
| 16 | #include <string.h> |
| 17 | #include <errno.h> |
| 18 | #include <time.h> |
| 19 | #include <termios.h> |
| 20 | #include <signal.h> |
| 21 | #include <sys/socket.h> |
| 22 | #include <sys/types.h> |
| 23 | #include <netinet/in.h> |
| 24 | #include <arpa/inet.h> |
| 25 | #include <netdb.h> |
| 26 | |
| 27 | #include "a.out.h" |
| 28 | #include "simulator.h" |
| 29 | |
| 30 | int |
| 31 | is_stdin_nonempty(void) |
| 32 | { |
| 33 | fd_set read_fds; |
| 34 | FD_ZERO(&read_fds); |
| 35 | FD_SET(STDIN_FILENO, &read_fds); |
| 36 | |
| 37 | struct timeval timeout; |
| 38 | timeout.tv_sec = 0; |
| 39 | timeout.tv_usec = 0; |
| 40 | |
| 41 | int retval = select(1, &read_fds, NULL, NULL, &timeout); |
| 42 | |
| 43 | if (retval == -1) { |
| 44 | /* TODO: How do I want to handle this error? */ |
| 45 | } |
| 46 | |
| 47 | return retval; |
| 48 | } |
| 49 | |
| 50 | uint32_t |
| 51 | generate_binary_psw(struct NEDstate * state) |
| 52 | { |
| 53 | uint32_t psw = 0; |
| 54 | if (state->active_thread->psw->zero) psw |= 0b1; |
| 55 | if (state->active_thread->psw->negative) psw |= 0b10; |
| 56 | return psw; |
| 57 | } |
| 58 | |
| 59 | void |
| 60 | ram_w_byte(struct NEDstate * state, uint32_t address, uint8_t data) |
| 61 | { |
| 62 | state->ram[address] = data; |
| 63 | } |
| 64 | |
| 65 | uint8_t |
| 66 | ram_r_byte(struct NEDstate * state, uint32_t address) |
| 67 | { |
| 68 | return state->ram[address]; |
| 69 | } |
| 70 | |
| 71 | /* For now, with only a terminal for IO, we pick off IO requests when accessing RAM. */ |
| 72 | /* TODO: Improve this before adding any other IO devices like disks. */ |
| 73 | |
| 74 | void |
| 75 | ram_w_word(struct NEDstate * state, uint32_t address, uint32_t data) |
| 76 | { |
| 77 | /* TODO: Since PC and PSW are memory mapped, they should accept writes. */ |
| 78 | /* Should writes to the PC automatically reset the syllable counter? */ |
| 79 | if (address == 0x8000000) { /* SLU: XBUF */ |
| 80 | printf("%c", data); |
| 81 | fflush(stdout); |
| 82 | } else if (address == 0x0 || address == 0x4) { |
| 83 | /* Intentionally empty */ |
| 84 | } else if (address >= 0x20000000) { |
| 85 | for (int i=3; i>=0; i--) { |
| 86 | uint8_t tmp_byte = ((data >> (8*(3-i))) & 0xff); |
| 87 | ram_w_byte(state,address+i,tmp_byte); |
| 88 | } |
| 89 | } |
| 90 | } |
| 91 | |
| 92 | uint32_t |
| 93 | ram_r_word(struct NEDstate * state, uint32_t address) |
| 94 | { |
| 95 | if (address == 0x0) { /* Zero register */ |
| 96 | return 0b0; |
| 97 | } else if (address == 0x4) { /* 0x80000000 register */ |
| 98 | return 0x80000000; |
| 99 | } else if (address == 0x8) { /* PC register */ |
| 100 | return state->active_thread->pc; |
| 101 | } else if (address == 0xC) { /* PSW register */ |
| 102 | return generate_binary_psw(state); |
| 103 | } else if (address == 0x8000004) { /* SLU: XCSR */ |
| 104 | /* TODO: Should I artificially restrict printing in the simulator? */ |
| 105 | /* It might help catch bugs like the GCC bug that slipped past SIMH. */ |
| 106 | return 0b1; |
| 107 | } else if (address == 0x8000008) { /* SLU: RBUF */ |
| 108 | if (is_stdin_nonempty()) { |
| 109 | return getchar(); |
| 110 | } else { |
| 111 | return (uint8_t)rand(); |
| 112 | } |
| 113 | } else if (address == 0x800000C) { /* SLU: RCSR */ |
| 114 | if (is_stdin_nonempty()) { |
| 115 | return 0b1; |
| 116 | } else { |
| 117 | return 0b0; |
| 118 | } |
| 119 | } else if (address >= 0x20000000) { /* RAM */ |
| 120 | uint32_t word = 0; |
| 121 | for (int i=0; i<4; i++) word |= (ram_r_byte(state,address+i)) << (8*(3-i)); |
| 122 | return word; |
| 123 | } |
| 124 | return 0b0; |
| 125 | } |
| 126 | |
| 127 | uint32_t |
| 128 | fetch_instruction_word(struct NEDstate * state) |
| 129 | { |
| 130 | uint32_t word = ram_r_word(state, state->active_thread->pc); |
| 131 | state->active_thread->pc += BPW; |
| 132 | return word; |
| 133 | } |
| 134 | |
| 135 | void |
| 136 | stack_w(struct NEDthread * thread, uint32_t value, uint8_t offset) |
| 137 | { |
| 138 | thread->stack[thread->sp - (offset + 1)] = value; |
| 139 | } |
| 140 | |
| 141 | uint32_t |
| 142 | stack_r(struct NEDthread * thread, uint8_t offset) |
| 143 | { |
| 144 | return thread->stack[thread->sp - (offset + 1)]; |
| 145 | } |
| 146 | |
| 147 | void |
| 148 | stack_push(struct NEDthread * thread, uint32_t value) |
| 149 | { |
| 150 | thread->stack[thread->sp++] = value; |
| 151 | } |
| 152 | |
| 153 | uint32_t |
| 154 | stack_pop(struct NEDthread * thread) |
| 155 | { |
| 156 | return thread->stack[--thread->sp]; |
| 157 | } |
| 158 | |
| 159 | void |
| 160 | set_psw_flags(uint32_t word, struct NEDstate * state) |
| 161 | { |
| 162 | if (word == 0) { |
| 163 | state->active_thread->psw->zero = true; |
| 164 | } else { |
| 165 | state->active_thread->psw->zero = false; |
| 166 | } |
| 167 | if (word & 0x80000000) { |
| 168 | state->active_thread->psw->negative = true; |
| 169 | } else { |
| 170 | state->active_thread->psw->negative = false; |
| 171 | } |
| 172 | } |
| 173 | |
| 174 | void |
| 175 | ned_instruction_and(struct NEDstate * state) |
| 176 | { |
| 177 | uint32_t operand1 = stack_pop(state->active_thread); |
| 178 | uint32_t operand2 = stack_pop(state->active_thread); |
| 179 | stack_push(state->active_thread, (operand1 & operand2)); |
| 180 | set_psw_flags(stack_r(state->active_thread,0), state); |
| 181 | } |
| 182 | |
| 183 | void |
| 184 | ned_instruction_or(struct NEDstate * state) |
| 185 | { |
| 186 | uint32_t operand1 = stack_pop(state->active_thread); |
| 187 | uint32_t operand2 = stack_pop(state->active_thread); |
| 188 | stack_push(state->active_thread, (operand1 | operand2)); |
| 189 | set_psw_flags(stack_r(state->active_thread,0), state); |
| 190 | } |
| 191 | |
| 192 | void |
| 193 | ned_instruction_not(struct NEDstate * state) |
| 194 | { |
| 195 | stack_push(state->active_thread, ~stack_pop(state->active_thread)); |
| 196 | set_psw_flags(stack_r(state->active_thread,0), state); |
| 197 | } |
| 198 | |
| 199 | void |
| 200 | ned_instruction_xor(struct NEDstate * state) |
| 201 | { |
| 202 | uint32_t operand1 = stack_pop(state->active_thread); |
| 203 | uint32_t operand2 = stack_pop(state->active_thread); |
| 204 | stack_push(state->active_thread, (operand1 ^ operand2)); |
| 205 | set_psw_flags(stack_r(state->active_thread,0), state); |
| 206 | } |
| 207 | |
| 208 | void |
| 209 | ned_instruction_add(struct NEDstate * state) |
| 210 | { |
| 211 | uint32_t operand1 = stack_pop(state->active_thread); |
| 212 | uint32_t operand2 = stack_pop(state->active_thread); |
| 213 | stack_push(state->active_thread, (operand1 + operand2)); |
| 214 | set_psw_flags(stack_r(state->active_thread,0), state); |
| 215 | } |
| 216 | |
| 217 | void |
| 218 | ned_instruction_mvstck(struct NEDstate * state) |
| 219 | { |
| 220 | uint32_t new_id = stack_pop(state->active_thread); |
| 221 | if (new_id < THREAD_COUNT) { |
| 222 | state->active_thread = state->thread[new_id]; |
| 223 | } else { |
| 224 | printf("ERROR: Attempted MVSTCK to ID higher than THREAD_COUNT.\n"); |
| 225 | state->halted = true; |
| 226 | } |
| 227 | } |
| 228 | |
| 229 | void |
| 230 | ned_instruction_shift(struct NEDstate * state) |
| 231 | { |
| 232 | /* TODO: Bounds check: Either all inputs are valid OR shift_by < 32. */ |
| 233 | /* I guess this also depends if I'm shifting-and-dropping, or barrel-shifting. */ |
| 234 | /* How should I pad for a right shift if I shift-and-drop? Sign extend? */ |
| 235 | uint32_t shift_by = stack_pop(state->active_thread); |
| 236 | uint32_t word = stack_pop(state->active_thread); |
| 237 | if (shift_by & 0x80000000) { |
| 238 | stack_push(state->active_thread, (word << (shift_by & 0x7fffffff))); |
| 239 | } else { |
| 240 | stack_push(state->active_thread, (word >> shift_by)); |
| 241 | } |
| 242 | set_psw_flags(stack_r(state->active_thread,0), state); |
| 243 | } |
| 244 | |
| 245 | void |
| 246 | ned_instruction_test(struct NEDstate * state) |
| 247 | { |
| 248 | uint32_t word = stack_pop(state->active_thread); |
| 249 | set_psw_flags(word, state); |
| 250 | } |
| 251 | |
| 252 | void |
| 253 | ned_instruction_jmp(struct NEDstate * state) |
| 254 | { |
| 255 | state->active_thread->pc = stack_pop(state->active_thread); |
| 256 | // The SC is caught and reset by the main loop since the PC changed. |
| 257 | } |
| 258 | |
| 259 | void |
| 260 | ned_instruction_swap(struct NEDstate * state) |
| 261 | { |
| 262 | uint32_t temp1 = stack_pop(state->active_thread); |
| 263 | uint32_t temp2 = stack_pop(state->active_thread); |
| 264 | stack_push(state->active_thread, temp1); |
| 265 | stack_push(state->active_thread, temp2); |
| 266 | set_psw_flags(stack_r(state->active_thread,0), state); |
| 267 | } |
| 268 | |
| 269 | void |
| 270 | ned_instruction_brz(struct NEDstate * state) |
| 271 | { |
| 272 | uint32_t new_pc = stack_pop(state->active_thread); |
| 273 | uint32_t test_word = stack_pop(state->active_thread); |
| 274 | if (test_word == 0) { |
| 275 | state->active_thread->pc = new_pc; |
| 276 | // The SC is caught and reset by the main loop since the PC changed. |
| 277 | } |
| 278 | } |
| 279 | |
| 280 | void |
| 281 | ned_instruction_load(struct NEDstate * state) |
| 282 | { |
| 283 | uint32_t address = stack_pop(state->active_thread); |
| 284 | stack_push(state->active_thread, ram_r_word(state, address)); |
| 285 | set_psw_flags(stack_r(state->active_thread,0), state); |
| 286 | } |
| 287 | |
| 288 | void |
| 289 | ned_instruction_store(struct NEDstate * state) |
| 290 | { |
| 291 | uint32_t address = stack_pop(state->active_thread); |
| 292 | uint32_t data = stack_pop(state->active_thread); |
| 293 | ram_w_word(state, address, data); |
| 294 | } |
| 295 | |
| 296 | void |
| 297 | ned_instruction_halt(struct NEDstate * state) |
| 298 | { |
| 299 | printf("Halting.\n"); |
| 300 | state->halted = true; |
| 301 | } |
| 302 | |
| 303 | void |
| 304 | execute_syllable(struct NEDstate * state, enum syllables syllable) |
| 305 | { |
| 306 | if (syllable & 0b100000) { /* Check the first bit of the syllable. 1 means IM_x. */ |
| 307 | stack_push(state->active_thread, (uint32_t)(syllable & 0b11111)); |
| 308 | } else if (syllable & 0b10000) { /* 1 in 2nd bit means LDSP+x or STSP+x instruction. */ |
| 309 | if (syllable & 0b1000) { /* LDSP+x */ |
| 310 | stack_push(state->active_thread,stack_r(state->active_thread,(syllable & 0b111))); |
| 311 | set_psw_flags(stack_r(state->active_thread,0), state); |
| 312 | } else { /* STSP+x */ |
| 313 | stack_w(state->active_thread,stack_pop(state->active_thread),(syllable & 0b111)); |
| 314 | } |
| 315 | } else { |
| 316 | switch (syllable) { |
| 317 | case AND: ned_instruction_and(state); break; |
| 318 | case OR: ned_instruction_or(state); break; |
| 319 | case NOT: ned_instruction_not(state); break; |
| 320 | case XOR: ned_instruction_xor(state); break; |
| 321 | case ADD: ned_instruction_add(state); break; |
| 322 | case MVSTCK: ned_instruction_mvstck(state); break; |
| 323 | case SHIFT: ned_instruction_shift(state); break; |
| 324 | case CMPSWP: /* TODO */ break; |
| 325 | case TEST: ned_instruction_test(state); break; |
| 326 | case JMP: ned_instruction_jmp(state); break; |
| 327 | case SWAP: ned_instruction_swap(state); break; |
| 328 | case BRZ: ned_instruction_brz(state); break; |
| 329 | case LOAD: ned_instruction_load(state); break; |
| 330 | case STORE: ned_instruction_store(state); break; |
| 331 | case NOP: /* Intentionally blank */ break; |
| 332 | case HALT: ned_instruction_halt(state); break; |
| 333 | default: |
| 334 | printf("ERROR: Attempted to execute illegal syllable: 0o%o\n", syllable); |
| 335 | state->halted = true; |
| 336 | break; |
| 337 | } |
| 338 | } |
| 339 | } |
| 340 | |
| 341 | uint8_t |
| 342 | extract_syllable_from_word(uint32_t word, uint8_t index) |
| 343 | { |
| 344 | uint32_t mask = 0b111111 << 6*(4-index); |
| 345 | return (word & mask) >> 6*(4-index); |
| 346 | } |
| 347 | |
| 348 | void |
| 349 | parse_aout_file(FILE * input, struct exec * aout_exec, uint8_t * text_segment, |
| 350 | struct nlist ** symbol_table, uint32_t * symbol_count) |
| 351 | { |
| 352 | uint32_t read_count = 0; |
| 353 | |
| 354 | /* Read in and check the a.out header. */ |
| 355 | for (uint32_t i=0; i<8; i++) { |
| 356 | switch (i) { |
| 357 | case 0: read_count = fread(&(aout_exec->a_midmag), 4, 1, input); break; |
| 358 | case 1: read_count = fread(&(aout_exec->a_text), 4, 1, input); break; |
| 359 | case 2: read_count = fread(&(aout_exec->a_data), 4, 1, input); break; |
| 360 | case 3: read_count = fread(&(aout_exec->a_bss), 4, 1, input); break; |
| 361 | case 4: read_count = fread(&(aout_exec->a_syms), 4, 1, input); break; |
| 362 | case 5: read_count = fread(&(aout_exec->a_entry), 4, 1, input); break; |
| 363 | case 6: read_count = fread(&(aout_exec->a_trsize), 4, 1, input); break; |
| 364 | case 7: read_count = fread(&(aout_exec->a_drsize), 4, 1, input); break; |
| 365 | } |
| 366 | if (read_count != 1) { |
| 367 | fprintf(stderr, "ERROR: Invalid a.out header.\n"); |
| 368 | exit(EXIT_FAILURE); |
| 369 | } |
| 370 | } |
| 371 | if (N_BADMAG(*aout_exec)) { |
| 372 | fprintf(stderr, "ERROR: Invalid magic number in a.out header.\n"); |
| 373 | exit(EXIT_FAILURE); |
| 374 | } else if (N_GETMID(*aout_exec) != MID_NED) { |
| 375 | fprintf(stderr, "ERROR: Executable not intended for NED Machine ID.\n"); |
| 376 | exit(EXIT_FAILURE); |
| 377 | } |
| 378 | |
| 379 | /* Read in the text segment. */ |
| 380 | uint32_t text_segment_size = (N_DATOFF(*aout_exec) - N_TXTOFF(*aout_exec)); |
| 381 | read_count = fread(text_segment, 1, text_segment_size, input); |
| 382 | if (read_count != text_segment_size) { |
| 383 | fprintf(stderr, "ERROR: Failed to read entire text segment.\n"); |
| 384 | exit(EXIT_FAILURE); |
| 385 | } |
| 386 | |
| 387 | /* Correct the byte order. */ |
| 388 | for (uint32_t i=0; i < (text_segment_size / 4); i++) { |
| 389 | uint8_t temp_word[4]; |
| 390 | for (uint8_t j=0; j<4; j++) temp_word[j] = text_segment[((i*4)+j)]; |
| 391 | for (uint8_t j=0; j<4; j++) text_segment[((i*4)+j)] = temp_word[(3-j)]; |
| 392 | } |
| 393 | |
| 394 | /* Read in the symbol table. */ |
| 395 | *symbol_count = ((N_STROFF(*aout_exec) - N_SYMOFF(*aout_exec)) / 20); /* 20 bytes per symbol. */ |
| 396 | *symbol_table = malloc((*symbol_count) * sizeof(struct nlist)); |
| 397 | for (uint32_t i=0; i < *symbol_count; i++) { |
| 398 | for (uint32_t j=0; j<5; j++) { |
| 399 | switch (j) { |
| 400 | case 0: read_count = fread(&((*symbol_table)[i].n_un.n_strx), 4, 1, input); break; |
| 401 | case 1: read_count = fread(&((*symbol_table)[i].n_type), 4, 1, input); break; |
| 402 | case 2: read_count = fread(&((*symbol_table)[i].n_other), 4, 1, input); break; |
| 403 | case 3: read_count = fread(&((*symbol_table)[i].n_desc), 4, 1, input); break; |
| 404 | case 4: read_count = fread(&((*symbol_table)[i].n_value), 4, 1, input); break; |
| 405 | } |
| 406 | if (read_count != 1) { |
| 407 | fprintf(stderr, "ERROR: Unable to read entire symbol table.\n"); |
| 408 | exit(EXIT_FAILURE); |
| 409 | } |
| 410 | } |
| 411 | } |
| 412 | |
| 413 | /* Read in the string table and update the symbol table entries with pointers to new strings. */ |
| 414 | uint32_t string_table_size; |
| 415 | read_count = fread(&string_table_size, 4, 1, input); |
| 416 | if (read_count != 1) { |
| 417 | fprintf(stderr, "ERROR: Failed to read string table size.\n"); |
| 418 | exit(EXIT_FAILURE); |
| 419 | } |
| 420 | for (uint32_t i=0; i < *symbol_count; i++) { |
| 421 | uint32_t len = 0; |
| 422 | if (i < ((*symbol_count)-1)) { |
| 423 | len = ((*symbol_table)[i+1].n_un.n_strx - (*symbol_table)[i].n_un.n_strx); |
| 424 | } else { |
| 425 | len = (string_table_size - (*symbol_table)[i].n_un.n_strx); |
| 426 | } |
| 427 | (*symbol_table)[i].n_un.n_name = malloc(len); |
| 428 | read_count = fread((*symbol_table)[i].n_un.n_name, 1, len, input); |
| 429 | if (read_count != len) { |
| 430 | fprintf(stderr, "ERROR: Failed to read a string from the string table.\n"); |
| 431 | exit(EXIT_FAILURE); |
| 432 | } |
| 433 | } |
| 434 | |
| 435 | } |
| 436 | |
| 437 | struct NEDstate * |
| 438 | init_simulator(void) |
| 439 | { |
| 440 | struct NEDstate * state = malloc(sizeof(struct NEDstate)); |
| 441 | state->hack = malloc(sizeof(struct NEDhack)); |
| 442 | for (size_t i=0; i < THREAD_COUNT; i++) { |
| 443 | state->thread[i] = malloc(sizeof(struct NEDthread)); |
| 444 | state->thread[i]->psw = malloc(sizeof(struct NEDpsw)); |
| 445 | } |
| 446 | state->thread[0]->pc = 0; |
| 447 | state->thread[0]->sc = 0; |
| 448 | state->thread[0]->sp = 0; |
| 449 | state->thread[0]->psw->zero = false; |
| 450 | state->thread[0]->psw->negative = false; |
| 451 | state->thread[0]->pc = 0x20000000; /* Data region starts 512 MB into address space. */ |
| 452 | state->active_thread = state->thread[0]; /* By convention, use thread 0 for init. */ |
| 453 | state->halted = false; |
| 454 | state->hack->resume_word = false; |
| 455 | |
| 456 | // TODO: This needs to be passed in as a CLI option. |
| 457 | #define AOUT_PATH "./test.out" |
| 458 | |
| 459 | /* Load an initial image into memory. */ |
| 460 | uint32_t address = 0x20000000; |
| 461 | struct exec aout_exec; |
| 462 | struct nlist * symbol_table; |
| 463 | uint32_t symbol_count; |
| 464 | FILE * input = NULL; |
| 465 | if ((input = fopen(AOUT_PATH, "r")) == NULL) { |
| 466 | fprintf(stderr, "ERROR: %s: %s\n", AOUT_PATH, strerror(errno)); |
| 467 | state->halted = true; |
| 468 | } |
| 469 | parse_aout_file(input, &aout_exec, &(state->ram[address]), &symbol_table, &symbol_count); |
| 470 | fclose(input); |
| 471 | |
| 472 | return state; |
| 473 | } |
| 474 | |
| 475 | struct NEDstate * |
| 476 | run_simulator(struct NEDstate * state) |
| 477 | { |
| 478 | if (state->halted) return state; |
| 479 | |
| 480 | /* Fetch instruction word. */ |
| 481 | uint32_t iw; |
| 482 | if (state->hack->resume_word) { |
| 483 | iw = state->hack->iw; |
| 484 | } else { |
| 485 | iw = fetch_instruction_word(state); |
| 486 | } |
| 487 | |
| 488 | /* Decode instruction word format and execute. */ |
| 489 | if (iw & (0b1 << 31)) { /* Instruction word is type A. */ |
| 490 | stack_push(state->active_thread, (iw << 1)); |
| 491 | } else if ((iw & (0b11 << 30)) == 0) { /* Instruction word is type C. */ |
| 492 | uint8_t syllable = extract_syllable_from_word(iw, state->active_thread->sc); |
| 493 | state->active_thread->sc++; // TODO: Should this be part of extract_syllable_from_word()? After all, incrementing the PC is done in fetch_instruction_word(). |
| 494 | uint32_t pre_execution_pc = state->active_thread->pc; // TODO: This is so we can catch JMP/JSR/etc subroutines that need the SC to be reset to zero. |
| 495 | execute_syllable(state, syllable); |
| 496 | if (state->active_thread->pc != pre_execution_pc) { |
| 497 | // Jumped to a new address, so prepare to execute a new instruction word. |
| 498 | state->active_thread->sc = 0; |
| 499 | state->hack->resume_word = false; |
| 500 | } else if (state->active_thread->sc >= SPW) { |
| 501 | // Just executed the last syllable in this word, time to follow the PC to the next word. |
| 502 | state->active_thread->sc = 0; |
| 503 | state->hack->resume_word = false; |
| 504 | } else { |
| 505 | // More syllables remain to be executed in this instruction word. |
| 506 | state->hack->resume_word = true; |
| 507 | state->hack->iw = iw; |
| 508 | } |
| 509 | } else { |
| 510 | state->halted = true; |
| 511 | fprintf(stderr, "WARNING: Halting due to attempted execution of illegal instruction.\n"); |
| 512 | } |
| 513 | |
| 514 | return state; |
| 515 | } |