├── LICENSE ├── README.md └── cc500.c /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 2, June 1991 3 | 4 | Copyright (C) 1989, 1991 Free Software Foundation, Inc., 5 | 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 6 | Everyone is permitted to copy and distribute verbatim copies 7 | of this license document, but changing it is not allowed. 8 | 9 | Preamble 10 | 11 | The licenses for most software are designed to take away your 12 | freedom to share and change it. By contrast, the GNU General Public 13 | License is intended to guarantee your freedom to share and change free 14 | software--to make sure the software is free for all its users. This 15 | General Public License applies to most of the Free Software 16 | Foundation's software and to any other program whose authors commit to 17 | using it. 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See the 304 | GNU General Public License for more details. 305 | 306 | You should have received a copy of the GNU General Public License along 307 | with this program; if not, write to the Free Software Foundation, Inc., 308 | 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. 309 | 310 | Also add information on how to contact you by electronic and paper mail. 311 | 312 | If the program is interactive, make it output a short notice like this 313 | when it starts in an interactive mode: 314 | 315 | Gnomovision version 69, Copyright (C) year name of author 316 | Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 317 | This is free software, and you are welcome to redistribute it 318 | under certain conditions; type `show c' for details. 319 | 320 | The hypothetical commands `show w' and `show c' should show the appropriate 321 | parts of the General Public License. Of course, the commands you use may 322 | be called something other than `show w' and `show c'; they could even be 323 | mouse-clicks or menu items--whatever suits your program. 324 | 325 | You should also get your employer (if you work as a programmer) or your 326 | school, if any, to sign a "copyright disclaimer" for the program, if 327 | necessary. Here is a sample; alter the names: 328 | 329 | Yoyodyne, Inc., hereby disclaims all copyright interest in the program 330 | `Gnomovision' (which makes passes at compilers) written by James Hacker. 331 | 332 | {signature of Ty Coon}, 1 April 1989 333 | Ty Coon, President of Vice 334 | 335 | This General Public License does not permit incorporating your program into 336 | proprietary programs. If your program is a subroutine library, you may 337 | consider it more useful to permit linking proprietary applications with the 338 | library. If this is what you want to do, use the GNU Lesser General 339 | Public License instead of this License. 340 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | cc500 2 | ===== 3 | 4 | CC500: a tiny self-hosting C compiler 5 | 6 | http://homepage.ntlworld.com/edmund.grimley-evans/cc500/ 7 | 8 | 9 | CC500: a tiny self-hosting C compiler 10 | 11 | Introduction 12 | 13 | I wrote this tiny compiler, which translates a subset of C into x86 machine code, for fun. It has no use, unless it counts as educational. I called it CC500 because I initally guessed it would take about 500 lines. It turned out to be about 600 lines even without the comments and blank lines. With the comments and blank lines it has about 750 lines. It could be made shorter, but I wanted the code to be clear and simple rather than obfuscated. 14 | 15 | Download 16 | 17 | cc500.c - just the code 18 | Compilation: 19 | 20 | gcc cc500.c -o cc500_1 21 | Self-compilation: 22 | 23 | ./cc500_1 < cc500.c > cc500_2 24 | chmod +x cc500_2 25 | How it works 26 | 27 | The compiler reads the whole program in C from stdin and writes an ELF binary for Linux/x86 to stdout. The ELF binary is somewhat non-standard as it consists of a single section that is both writable and executable. It seems to work for me on a real Linux box, but it might cause problems on an emulator. 28 | 29 | No libraries are used. Tiny, machine-code implementations of exit(), getchar(), malloc() and putchar() are included in the binary that is generated. There is no free() as malloc() is just sbrk(), really, implemented with two calls to brk(). 30 | 31 | There is almost no error-checking. With some invalid C programs the compiler calls exit(1) instead of generating a binary, but in most cases it generates a binary that crashes when you run it. 32 | 33 | There is no preprocessor. The lexer looks for tokens that match one of the following Perl regular expressions: /[a-z0-9_]+/, /[<=>|&!]+/, /'[^']*'/, /"[^"]*"/, /./. Traditional C-style comments are handled, but not C++-style comments. 34 | 35 | The symbol table is implemented with a single array of char. The type of each symbol is recorded as 'D' (defined global), 'U' (undefined global), 'L' (local variable) or 'A' (argument of a function) - see sym_get_value(). There is also an address recorded for each symbol, but no type, as there is no type-checking and all arrays are assumed to be arrays of char. The address of an 'L' or 'A' is its position on the stack. The address of a 'D' is the position of that function or global variable in the binary. The address of a 'U' is also a pointer into the binary, but a pointer to where the symbol was last used and the head of a linked list of all the forward references to that symbol. 36 | 37 | Scoping rules for local variables are implemented correctly as it is easy to do so: at the end of a compound statement the pointer to the end of the symbol table is restored to what it was at the start of the compound statement - see the assignment to table_pos in statement(). 38 | 39 | I started off writing CC500 without local variables, but it felt very unnatural. Nested scopes are an essential part of C and it is not easy to write a recursive-descent parser without automatic variables. 40 | 41 | It is assumed that all variables, arguments and return values are char * or int, though the compiler does not even parse the types, let alone record them in the symbol table. The functions that implement the recursive-descent parser return 1, 2 or 3, corresponding to a "char lval", "int lval" or "other" - see promote(). 42 | 43 | Each parsing function is preceded by a comment that documents the syntactic structures recognised, in an obvious notation. In some cases the code accepts additional, incorrect structures in addition to what is documented in the comment. Only a tiny subset of C's operators are accepted: just the ones I needed while writing the compiler. There are no unary operators: instead of the indirection operator * you must use x[y], where it is assumed that x is char * and y is int. The only statements recognised are compound statements, expressions, if, while and return. Local variable declarations, with initialisers, are treated as a kind of statement. (If you write something like if (x) int y; the compiler will not complain, but the binary will crash.) 44 | 45 | There are no arbitary limits on the length of symbols, number of symbols are the like: all three buffers (token, table and code) are supposed to be automatically extended as required by calls to my_realloc(). 46 | 47 | Extending it 48 | 49 | Some simple and obvious enhancements would be to print an appropriate message message when an error is detected, check for undefined globals, and allow main() to be anywhere in the file. 50 | 51 | It would be easy to extend the compiler to handle the remaining operators and statement types of C. To implement break and continue you would probably add additional arguments to the parsing functions that record the address and stack height of the current loop. The easiest way to implement switch statements might be to add an argument that records the location of the previous case label in the current switch statement; a case label would then be translated with a comparison and a branch forwards to the next case label. In general, C is quite amenable to direct translation into machine code without going through an IR (intermediate representation). 52 | 53 | Extending the type system would be a bit more challenging. You could correctly implement scalars and pointers, with type checking, by adding a single integer field to the symbol table to record the type. However, if you wanted to implement structs, or function pointers with proper type checking, you would need a recursive data structure to represent the types. It is interesting, but not really surprising, that you start to start to need structs in the implementation language at roughly the same point that you start to implement them. However, C's types get interesting even without structs, unions and typedefs. For example, void (*(*f())(void (*)(void)))(void); declares a function that returns a pointer to a function that takes a pointer to a function as an argument and returns another pointer to a function. I must admit to finding that part of C's syntax rather difficult to parse mentally. I'm glad we have computers to do it for us. 54 | 55 | Links 56 | 57 | bcompiler - Bootstrapping a simple compiler from nothing 58 | OTCC - The smallest self compiling pseudo C compiler 59 | Tiny ELF programs by Brian Raiter 60 | Edmund Grimley Evans 61 | -------------------------------------------------------------------------------- /cc500.c: -------------------------------------------------------------------------------- 1 | /* 2 | * Copyright (C) 2006 Edmund GRIMLEY EVANS 3 | * 4 | * This program is free software; you can redistribute it and/or modify 5 | * it under the terms of the GNU General Public License as published by 6 | * the Free Software Foundation; either version 2 of the License, or 7 | * (at your option) any later version. 8 | * 9 | * This program is distributed in the hope that it will be useful, 10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 | * GNU General Public License for more details. 13 | * 14 | * You should have received a copy of the GNU General Public License 15 | * along with this program; if not, write to the Free Software 16 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 17 | */ 18 | 19 | /* 20 | * A self-compiling compiler for a small subset of C. 21 | */ 22 | 23 | /* Our library functions. */ 24 | void exit(int); 25 | int getchar(void); 26 | void *malloc(int); 27 | int putchar(int); 28 | 29 | /* The first thing defined must be main(). */ 30 | int main1(); 31 | int main() 32 | { 33 | return main1(); 34 | } 35 | 36 | char *my_realloc(char *old, int oldlen, int newlen) 37 | { 38 | char *new = malloc(newlen); 39 | int i = 0; 40 | while (i <= oldlen - 1) { 41 | new[i] = old[i]; 42 | i = i + 1; 43 | } 44 | return new; 45 | } 46 | 47 | int nextc; 48 | char *token; 49 | int token_size; 50 | 51 | void error() 52 | { 53 | exit(1); 54 | } 55 | 56 | int i; 57 | 58 | void takechar() 59 | { 60 | if (token_size <= i + 1) { 61 | int x = (i + 10) << 1; 62 | token = my_realloc(token, token_size, x); 63 | token_size = x; 64 | } 65 | token[i] = nextc; 66 | i = i + 1; 67 | nextc = getchar(); 68 | } 69 | 70 | void get_token() 71 | { 72 | int w = 1; 73 | while (w) { 74 | w = 0; 75 | while ((nextc == ' ') | (nextc == 9) | (nextc == 10)) 76 | nextc = getchar(); 77 | i = 0; 78 | while ((('a' <= nextc) & (nextc <= 'z')) | 79 | (('0' <= nextc) & (nextc <= '9')) | (nextc == '_')) 80 | takechar(); 81 | if (i == 0) 82 | while ((nextc == '<') | (nextc == '=') | (nextc == '>') | 83 | (nextc == '|') | (nextc == '&') | (nextc == '!')) 84 | takechar(); 85 | if (i == 0) { 86 | if (nextc == 39) { 87 | takechar(); 88 | while (nextc != 39) 89 | takechar(); 90 | takechar(); 91 | } 92 | else if (nextc == '"') { 93 | takechar(); 94 | while (nextc != '"') 95 | takechar(); 96 | takechar(); 97 | } 98 | else if (nextc == '/') { 99 | takechar(); 100 | if (nextc == '*') { 101 | nextc = getchar(); 102 | while (nextc != '/') { 103 | while (nextc != '*') 104 | nextc = getchar(); 105 | nextc = getchar(); 106 | } 107 | nextc = getchar(); 108 | w = 1; 109 | } 110 | } 111 | else if (nextc != 0-1) 112 | takechar(); 113 | } 114 | token[i] = 0; 115 | } 116 | } 117 | 118 | int peek(char *s) 119 | { 120 | int i = 0; 121 | while ((s[i] == token[i]) & (s[i] != 0)) 122 | i = i + 1; 123 | return s[i] == token[i]; 124 | } 125 | 126 | int accept(char *s) 127 | { 128 | if (peek(s)) { 129 | get_token(); 130 | return 1; 131 | } 132 | else 133 | return 0; 134 | } 135 | 136 | void expect(char *s) 137 | { 138 | if (accept(s) == 0) 139 | error(); 140 | } 141 | 142 | char *code; 143 | int code_size; 144 | int codepos; 145 | int code_offset; 146 | 147 | void save_int(char *p, int n) 148 | { 149 | p[0] = n; 150 | p[1] = n >> 8; 151 | p[2] = n >> 16; 152 | p[3] = n >> 24; 153 | } 154 | 155 | int load_int(char *p) 156 | { 157 | return ((p[0] & 255) + ((p[1] & 255) << 8) + 158 | ((p[2] & 255) << 16) + ((p[3] & 255) << 24)); 159 | } 160 | 161 | void emit(int n, char *s) 162 | { 163 | i = 0; 164 | if (code_size <= codepos + n) { 165 | int x = (codepos + n) << 1; 166 | code = my_realloc(code, code_size, x); 167 | code_size = x; 168 | } 169 | while (i <= n - 1) { 170 | code[codepos] = s[i]; 171 | codepos = codepos + 1; 172 | i = i + 1; 173 | } 174 | } 175 | 176 | void be_push() 177 | { 178 | emit(1, "\x50"); /* push %eax */ 179 | } 180 | 181 | void be_pop(int n) 182 | { 183 | emit(6, "\x81\xc4...."); /* add $(n * 4),%esp */ 184 | save_int(code + codepos - 4, n << 2); 185 | } 186 | 187 | char *table; 188 | int table_size; 189 | int table_pos; 190 | int stack_pos; 191 | 192 | int sym_lookup(char *s) 193 | { 194 | int t = 0; 195 | int current_symbol = 0; 196 | while (t <= table_pos - 1) { 197 | i = 0; 198 | while ((s[i] == table[t]) & (s[i] != 0)) { 199 | i = i + 1; 200 | t = t + 1; 201 | } 202 | if (s[i] == table[t]) 203 | current_symbol = t; 204 | while (table[t] != 0) 205 | t = t + 1; 206 | t = t + 6; 207 | } 208 | return current_symbol; 209 | } 210 | 211 | void sym_declare(char *s, int type, int value) 212 | { 213 | int t = table_pos; 214 | i = 0; 215 | while (s[i] != 0) { 216 | if (table_size <= t + 10) { 217 | int x = (t + 10) << 1; 218 | table = my_realloc(table, table_size, x); 219 | table_size = x; 220 | } 221 | table[t] = s[i]; 222 | i = i + 1; 223 | t = t + 1; 224 | } 225 | table[t] = 0; 226 | table[t + 1] = type; 227 | save_int(table + t + 2, value); 228 | table_pos = t + 6; 229 | } 230 | 231 | int sym_declare_global(char *s) 232 | { 233 | int current_symbol = sym_lookup(s); 234 | if (current_symbol == 0) { 235 | sym_declare(s, 'U', code_offset); 236 | current_symbol = table_pos - 6; 237 | } 238 | return current_symbol; 239 | } 240 | 241 | void sym_define_global(int current_symbol) 242 | { 243 | int i; 244 | int j; 245 | int t = current_symbol; 246 | int v = codepos + code_offset; 247 | if (table[t + 1] != 'U') 248 | error(); /* symbol redefined */ 249 | i = load_int(table + t + 2) - code_offset; 250 | while (i) { 251 | j = load_int(code + i) - code_offset; 252 | save_int(code + i, v); 253 | i = j; 254 | } 255 | table[t + 1] = 'D'; 256 | save_int(table + t + 2, v); 257 | } 258 | 259 | int number_of_args; 260 | 261 | void sym_get_value(char *s) 262 | { 263 | int t; 264 | if ((t = sym_lookup(s)) == 0) 265 | error(); 266 | emit(5, "\xb8...."); /* mov $n,%eax */ 267 | save_int(code + codepos - 4, load_int(table + t + 2)); 268 | if (table[t + 1] == 'D') { /* defined global */ 269 | } 270 | else if (table[t + 1] == 'U') /* undefined global */ 271 | save_int(table + t + 2, codepos + code_offset - 4); 272 | else if (table[t + 1] == 'L') { /* local variable */ 273 | int k = (stack_pos - table[t + 2] - 1) << 2; 274 | emit(7, "\x8d\x84\x24...."); /* lea (n * 4)(%esp),%eax */ 275 | save_int(code + codepos - 4, k); 276 | } 277 | else if (table[t + 1] == 'A') { /* argument */ 278 | int k = (stack_pos + number_of_args - table[t + 2] + 1) << 2; 279 | emit(7, "\x8d\x84\x24...."); /* lea (n * 4)(%esp),%eax */ 280 | save_int(code + codepos - 4, k); 281 | } 282 | else 283 | error(); 284 | } 285 | 286 | void be_start() 287 | { 288 | emit(16, "\x7f\x45\x4c\x46\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00"); 289 | emit(16, "\x02\x00\x03\x00\x01\x00\x00\x00\x54\x80\x04\x08\x34\x00\x00\x00"); 290 | emit(16, "\x00\x00\x00\x00\x00\x00\x00\x00\x34\x00\x20\x00\x01\x00\x00\x00"); 291 | emit(16, "\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x80\x04\x08"); 292 | emit(16, "\x00\x80\x04\x08\x10\x4b\x00\x00\x10\x4b\x00\x00\x07\x00\x00\x00"); 293 | emit(16, "\x00\x10\x00\x00\xe8\x00\x00\x00\x00\x89\xc3\x31\xc0\x40\xcd\x80"); 294 | 295 | sym_define_global(sym_declare_global("exit")); 296 | /* pop %ebx ; pop %ebx ; xor %eax,%eax ; inc %eax ; int $0x80 */ 297 | emit(7, "\x5b\x5b\x31\xc0\x40\xcd\x80"); 298 | 299 | sym_define_global(sym_declare_global("getchar")); 300 | /* mov $3,%eax ; xor %ebx,%ebx ; push %ebx ; mov %esp,%ecx */ 301 | emit(10, "\xb8\x03\x00\x00\x00\x31\xdb\x53\x89\xe1"); 302 | /* xor %edx,%edx ; inc %edx ; int $0x80 */ 303 | /* test %eax,%eax ; pop %eax ; jne . + 7 */ 304 | emit(10, "\x31\xd2\x42\xcd\x80\x85\xc0\x58\x75\x05"); 305 | /* mov $-1,%eax ; ret */ 306 | emit(6, "\xb8\xff\xff\xff\xff\xc3"); 307 | 308 | sym_define_global(sym_declare_global("malloc")); 309 | /* mov 4(%esp),%eax */ 310 | emit(4, "\x8b\x44\x24\x04"); 311 | /* push %eax ; xor %ebx,%ebx ; mov $45,%eax ; int $0x80 */ 312 | emit(10, "\x50\x31\xdb\xb8\x2d\x00\x00\x00\xcd\x80"); 313 | /* pop %ebx ; add %eax,%ebx ; push %eax ; push %ebx ; mov $45,%eax */ 314 | emit(10, "\x5b\x01\xc3\x50\x53\xb8\x2d\x00\x00\x00"); 315 | /* int $0x80 ; pop %ebx ; cmp %eax,%ebx ; pop %eax ; je . + 7 */ 316 | emit(8, "\xcd\x80\x5b\x39\xc3\x58\x74\x05"); 317 | /* mov $-1,%eax ; ret */ 318 | emit(6, "\xb8\xff\xff\xff\xff\xc3"); 319 | 320 | sym_define_global(sym_declare_global("putchar")); 321 | /* mov $4,%eax ; xor %ebx,%ebx ; inc %ebx */ 322 | emit(8, "\xb8\x04\x00\x00\x00\x31\xdb\x43"); 323 | /* lea 4(%esp),%ecx ; mov %ebx,%edx ; int $0x80 ; ret */ 324 | emit(9, "\x8d\x4c\x24\x04\x89\xda\xcd\x80\xc3"); 325 | 326 | save_int(code + 85, codepos - 89); /* entry set to first thing in file */ 327 | } 328 | 329 | void be_finish() 330 | { 331 | save_int(code + 68, codepos); 332 | save_int(code + 72, codepos); 333 | i = 0; 334 | while (i <= codepos - 1) { 335 | putchar(code[i]); 336 | i = i + 1; 337 | } 338 | } 339 | 340 | void promote(int type) 341 | { 342 | /* 1 = char lval, 2 = int lval, 3 = other */ 343 | if (type == 1) 344 | emit(3, "\x0f\xbe\x00"); /* movsbl (%eax),%eax */ 345 | else if (type == 2) 346 | emit(2, "\x8b\x00"); /* mov (%eax),%eax */ 347 | } 348 | 349 | int expression(); 350 | 351 | /* 352 | * primary-expr: 353 | * identifier 354 | * constant 355 | * ( expression ) 356 | */ 357 | int primary_expr() 358 | { 359 | int type; 360 | if (('0' <= token[0]) & (token[0] <= '9')) { 361 | int n = 0; 362 | i = 0; 363 | while (token[i]) { 364 | n = (n << 1) + (n << 3) + token[i] - '0'; 365 | i = i + 1; 366 | } 367 | emit(5, "\xb8...."); /* mov $x,%eax */ 368 | save_int(code + codepos - 4, n); 369 | type = 3; 370 | } 371 | else if (('a' <= token[0]) & (token[0] <= 'z')) { 372 | sym_get_value(token); 373 | type = 2; 374 | } 375 | else if (accept("(")) { 376 | type = expression(); 377 | if (peek(")") == 0) 378 | error(); 379 | } 380 | else if ((token[0] == 39) & (token[1] != 0) & 381 | (token[2] == 39) & (token[3] == 0)) { 382 | emit(5, "\xb8...."); /* mov $x,%eax */ 383 | save_int(code + codepos - 4, token[1]); 384 | type = 3; 385 | } 386 | else if (token[0] == '"') { 387 | int i = 0; 388 | int j = 1; 389 | int k; 390 | while (token[j] != '"') { 391 | if ((token[j] == 92) & (token[j + 1] == 'x')) { 392 | if (token[j + 2] <= '9') 393 | k = token[j + 2] - '0'; 394 | else 395 | k = token[j + 2] - 'a' + 10; 396 | k = k << 4; 397 | if (token[j + 3] <= '9') 398 | k = k + token[j + 3] - '0'; 399 | else 400 | k = k + token[j + 3] - 'a' + 10; 401 | token[i] = k; 402 | j = j + 4; 403 | } 404 | else { 405 | token[i] = token[j]; 406 | j = j + 1; 407 | } 408 | i = i + 1; 409 | } 410 | token[i] = 0; 411 | /* call ... ; the string ; pop %eax */ 412 | emit(5, "\xe8...."); 413 | save_int(code + codepos - 4, i + 1); 414 | emit(i + 1, token); 415 | emit(1, "\x58"); 416 | type = 3; 417 | } 418 | else 419 | error(); 420 | get_token(); 421 | return type; 422 | } 423 | 424 | void binary1(int type) 425 | { 426 | promote(type); 427 | be_push(); 428 | stack_pos = stack_pos + 1; 429 | } 430 | 431 | int binary2(int type, int n, char *s) 432 | { 433 | promote(type); 434 | emit(n, s); 435 | stack_pos = stack_pos - 1; 436 | return 3; 437 | } 438 | 439 | /* 440 | * postfix-expr: 441 | * primary-expr 442 | * postfix-expr [ expression ] 443 | * postfix-expr ( expression-list-opt ) 444 | */ 445 | int postfix_expr() 446 | { 447 | int type = primary_expr(); 448 | if (accept("[")) { 449 | binary1(type); /* pop %ebx ; add %ebx,%eax */ 450 | binary2(expression(), 3, "\x5b\x01\xd8"); 451 | expect("]"); 452 | type = 1; 453 | } 454 | else if (accept("(")) { 455 | int s = stack_pos; 456 | be_push(); 457 | stack_pos = stack_pos + 1; 458 | if (accept(")") == 0) { 459 | promote(expression()); 460 | be_push(); 461 | stack_pos = stack_pos + 1; 462 | while (accept(",")) { 463 | promote(expression()); 464 | be_push(); 465 | stack_pos = stack_pos + 1; 466 | } 467 | expect(")"); 468 | } 469 | emit(7, "\x8b\x84\x24...."); /* mov (n * 4)(%esp),%eax */ 470 | save_int(code + codepos - 4, (stack_pos - s - 1) << 2); 471 | emit(2, "\xff\xd0"); /* call *%eax */ 472 | be_pop(stack_pos - s); 473 | stack_pos = s; 474 | type = 3; 475 | } 476 | return type; 477 | } 478 | 479 | /* 480 | * additive-expr: 481 | * postfix-expr 482 | * additive-expr + postfix-expr 483 | * additive-expr - postfix-expr 484 | */ 485 | int additive_expr() 486 | { 487 | int type = postfix_expr(); 488 | while (1) { 489 | if (accept("+")) { 490 | binary1(type); /* pop %ebx ; add %ebx,%eax */ 491 | type = binary2(postfix_expr(), 3, "\x5b\x01\xd8"); 492 | } 493 | else if (accept("-")) { 494 | binary1(type); /* pop %ebx ; sub %eax,%ebx ; mov %ebx,%eax */ 495 | type = binary2(postfix_expr(), 5, "\x5b\x29\xc3\x89\xd8"); 496 | } 497 | else 498 | return type; 499 | } 500 | } 501 | 502 | /* 503 | * shift-expr: 504 | * additive-expr 505 | * shift-expr << additive-expr 506 | * shift-expr >> additive-expr 507 | */ 508 | int shift_expr() 509 | { 510 | int type = additive_expr(); 511 | while (1) { 512 | if (accept("<<")) { 513 | binary1(type); /* mov %eax,%ecx ; pop %eax ; shl %cl,%eax */ 514 | type = binary2(additive_expr(), 5, "\x89\xc1\x58\xd3\xe0"); 515 | } 516 | else if (accept(">>")) { 517 | binary1(type); /* mov %eax,%ecx ; pop %eax ; sar %cl,%eax */ 518 | type = binary2(additive_expr(), 5, "\x89\xc1\x58\xd3\xf8"); 519 | } 520 | else 521 | return type; 522 | } 523 | } 524 | 525 | /* 526 | * relational-expr: 527 | * shift-expr 528 | * relational-expr <= shift-expr 529 | */ 530 | int relational_expr() 531 | { 532 | int type = shift_expr(); 533 | while (accept("<=")) { 534 | binary1(type); 535 | /* pop %ebx ; cmp %eax,%ebx ; setle %al ; movzbl %al,%eax */ 536 | type = binary2(shift_expr(), 537 | 9, "\x5b\x39\xc3\x0f\x9e\xc0\x0f\xb6\xc0"); 538 | } 539 | return type; 540 | } 541 | 542 | /* 543 | * equality-expr: 544 | * relational-expr 545 | * equality-expr == relational-expr 546 | * equality-expr != relational-expr 547 | */ 548 | int equality_expr() 549 | { 550 | int type = relational_expr(); 551 | while (1) { 552 | if (accept("==")) { 553 | binary1(type); 554 | /* pop %ebx ; cmp %eax,%ebx ; sete %al ; movzbl %al,%eax */ 555 | type = binary2(relational_expr(), 556 | 9, "\x5b\x39\xc3\x0f\x94\xc0\x0f\xb6\xc0"); 557 | } 558 | else if (accept("!=")) { 559 | binary1(type); 560 | /* pop %ebx ; cmp %eax,%ebx ; setne %al ; movzbl %al,%eax */ 561 | type = binary2(relational_expr(), 562 | 9, "\x5b\x39\xc3\x0f\x95\xc0\x0f\xb6\xc0"); 563 | } 564 | else 565 | return type; 566 | } 567 | } 568 | 569 | /* 570 | * bitwise-and-expr: 571 | * equality-expr 572 | * bitwise-and-expr & equality-expr 573 | */ 574 | int bitwise_and_expr() 575 | { 576 | int type = equality_expr(); 577 | while (accept("&")) { 578 | binary1(type); /* pop %ebx ; and %ebx,%eax */ 579 | type = binary2(equality_expr(), 3, "\x5b\x21\xd8"); 580 | } 581 | return type; 582 | } 583 | 584 | /* 585 | * bitwise-or-expr: 586 | * bitwise-and-expr 587 | * bitwise-and-expr | bitwise-or-expr 588 | */ 589 | int bitwise_or_expr() 590 | { 591 | int type = bitwise_and_expr(); 592 | while (accept("|")) { 593 | binary1(type); /* pop %ebx ; or %ebx,%eax */ 594 | type = binary2(bitwise_and_expr(), 3, "\x5b\x09\xd8"); 595 | } 596 | return type; 597 | } 598 | 599 | /* 600 | * expression: 601 | * bitwise-or-expr 602 | * bitwise-or-expr = expression 603 | */ 604 | int expression() 605 | { 606 | int type = bitwise_or_expr(); 607 | if (accept("=")) { 608 | be_push(); 609 | stack_pos = stack_pos + 1; 610 | promote(expression()); 611 | if (type == 2) 612 | emit(3, "\x5b\x89\x03"); /* pop %ebx ; mov %eax,(%ebx) */ 613 | else 614 | emit(3, "\x5b\x88\x03"); /* pop %ebx ; mov %al,(%ebx) */ 615 | stack_pos = stack_pos - 1; 616 | type = 3; 617 | } 618 | return type; 619 | } 620 | 621 | /* 622 | * type-name: 623 | * char * 624 | * int 625 | */ 626 | void type_name() 627 | { 628 | get_token(); 629 | while (accept("*")) { 630 | } 631 | } 632 | 633 | /* 634 | * statement: 635 | * { statement-list-opt } 636 | * type-name identifier ; 637 | * type-name identifier = expression; 638 | * if ( expression ) statement 639 | * if ( expression ) statement else statement 640 | * while ( expression ) statement 641 | * return ; 642 | * expr ; 643 | */ 644 | void statement() 645 | { 646 | int p1; 647 | int p2; 648 | if (accept("{")) { 649 | int n = table_pos; 650 | int s = stack_pos; 651 | while (accept("}") == 0) 652 | statement(); 653 | table_pos = n; 654 | be_pop(stack_pos - s); 655 | stack_pos = s; 656 | } 657 | else if (peek("char") | peek("int")) { 658 | type_name(); 659 | sym_declare(token, 'L', stack_pos); 660 | get_token(); 661 | if (accept("=")) 662 | promote(expression()); 663 | expect(";"); 664 | be_push(); 665 | stack_pos = stack_pos + 1; 666 | } 667 | else if (accept("if")) { 668 | expect("("); 669 | promote(expression()); 670 | emit(8, "\x85\xc0\x0f\x84...."); /* test %eax,%eax ; je ... */ 671 | p1 = codepos; 672 | expect(")"); 673 | statement(); 674 | emit(5, "\xe9...."); /* jmp ... */ 675 | p2 = codepos; 676 | save_int(code + p1 - 4, codepos - p1); 677 | if (accept("else")) 678 | statement(); 679 | save_int(code + p2 - 4, codepos - p2); 680 | } 681 | else if (accept("while")) { 682 | expect("("); 683 | p1 = codepos; 684 | promote(expression()); 685 | emit(8, "\x85\xc0\x0f\x84...."); /* test %eax,%eax ; je ... */ 686 | p2 = codepos; 687 | expect(")"); 688 | statement(); 689 | emit(5, "\xe9...."); /* jmp ... */ 690 | save_int(code + codepos - 4, p1 - codepos); 691 | save_int(code + p2 - 4, codepos - p2); 692 | } 693 | else if (accept("return")) { 694 | if (peek(";") == 0) 695 | promote(expression()); 696 | expect(";"); 697 | be_pop(stack_pos); 698 | emit(1, "\xc3"); /* ret */ 699 | } 700 | else { 701 | expression(); 702 | expect(";"); 703 | } 704 | } 705 | 706 | /* 707 | * program: 708 | * declaration 709 | * declaration program 710 | * 711 | * declaration: 712 | * type-name identifier ; 713 | * type-name identifier ( parameter-list ) ; 714 | * type-name identifier ( parameter-list ) statement 715 | * 716 | * parameter-list: 717 | * parameter-declaration 718 | * parameter-list, parameter-declaration 719 | * 720 | * parameter-declaration: 721 | * type-name identifier-opt 722 | */ 723 | void program() 724 | { 725 | int current_symbol; 726 | while (token[0]) { 727 | type_name(); 728 | current_symbol = sym_declare_global(token); 729 | get_token(); 730 | if (accept(";")) { 731 | sym_define_global(current_symbol); 732 | emit(4, "\x00\x00\x00\x00"); 733 | } 734 | else if (accept("(")) { 735 | int n = table_pos; 736 | number_of_args = 0; 737 | while (accept(")") == 0) { 738 | number_of_args = number_of_args + 1; 739 | type_name(); 740 | if (peek(")") == 0) { 741 | sym_declare(token, 'A', number_of_args); 742 | get_token(); 743 | } 744 | accept(","); /* ignore trailing comma */ 745 | } 746 | if (accept(";") == 0) { 747 | sym_define_global(current_symbol); 748 | statement(); 749 | emit(1, "\xc3"); /* ret */ 750 | } 751 | table_pos = n; 752 | } 753 | else 754 | error(); 755 | } 756 | } 757 | 758 | int main1() 759 | { 760 | code_offset = 134512640; /* 0x08048000 */ 761 | be_start(); 762 | nextc = getchar(); 763 | get_token(); 764 | program(); 765 | be_finish(); 766 | return 0; 767 | } 768 | --------------------------------------------------------------------------------