1 /* alloca.c -- allocate automatically reclaimed memory 2 (Mostly) portable public-domain implementation -- D A Gwyn 3 4 This implementation of the PWB library alloca function, 5 which is used to allocate space off the run-time stack so 6 that it is automatically reclaimed upon procedure exit, 7 was inspired by discussions with J. Q. Johnson of Cornell. 8 J.Otto Tennant <jot (at) cray.com> contributed the Cray support. 9 10 There are some preprocessor constants that can 11 be defined when compiling for your specific system, for 12 improved efficiency; however, the defaults should be okay. 13 14 The general concept of this implementation is to keep 15 track of all alloca-allocated blocks, and reclaim any 16 that are found to be deeper in the stack than the current 17 invocation. This heuristic does not reclaim storage as 18 soon as it becomes invalid, but it will do so eventually. 19 20 As a special case, alloca(0) reclaims storage without 21 allocating any. It is a good idea to use alloca(0) in 22 your main control loop, etc. to force garbage collection. */ 23 24 #ifdef HAVE_CONFIG_H 25 #include <config.h> 26 #endif 27 28 #ifdef HAVE_STRING_H 29 #include <string.h> 30 #endif 31 #ifdef HAVE_STDLIB_H 32 #include <stdlib.h> 33 #endif 34 35 #ifdef emacs 36 #include "blockinput.h" 37 #endif 38 39 /* If compiling with GCC 2, this file's not needed. */ 40 #if !defined (__GNUC__) || __GNUC__ < 2 41 42 /* If someone has defined alloca as a macro, 43 there must be some other way alloca is supposed to work. */ 44 #ifndef alloca 45 46 #ifdef emacs 47 #ifdef static 48 /* actually, only want this if static is defined as "" 49 -- this is for usg, in which emacs must undefine static 50 in order to make unexec workable 51 */ 52 #ifndef STACK_DIRECTION 53 you 54 lose 55 -- must know STACK_DIRECTION at compile-time 56 #endif /* STACK_DIRECTION undefined */ 57 #endif /* static */ 58 #endif /* emacs */ 59 60 /* If your stack is a linked list of frames, you have to 61 provide an "address metric" ADDRESS_FUNCTION macro. */ 62 63 #if defined (CRAY) && defined (CRAY_STACKSEG_END) 64 long i00afunc (); 65 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) 66 #else 67 #define ADDRESS_FUNCTION(arg) &(arg) 68 #endif 69 70 #if __STDC__ 71 typedef void *pointer; 72 #else 73 typedef char *pointer; 74 #endif 75 76 #ifndef NULL 77 #define NULL 0 78 #endif 79 80 /* Different portions of Emacs need to call different versions of 81 malloc. The Emacs executable needs alloca to call xmalloc, because 82 ordinary malloc isn't protected from input signals. On the other 83 hand, the utilities in lib-src need alloca to call malloc; some of 84 them are very simple, and don't have an xmalloc routine. 85 86 Non-Emacs programs expect this to call use xmalloc. 87 88 Callers below should use malloc. */ 89 90 #ifndef emacs 91 #define malloc xmalloc 92 #endif 93 extern pointer malloc (); 94 95 /* Define STACK_DIRECTION if you know the direction of stack 96 growth for your system; otherwise it will be automatically 97 deduced at run-time. 98 99 STACK_DIRECTION > 0 => grows toward higher addresses 100 STACK_DIRECTION < 0 => grows toward lower addresses 101 STACK_DIRECTION = 0 => direction of growth unknown */ 102 103 #ifndef STACK_DIRECTION 104 #define STACK_DIRECTION 0 /* Direction unknown. */ 105 #endif 106 107 #if STACK_DIRECTION != 0 108 109 #define STACK_DIR STACK_DIRECTION /* Known at compile-time. */ 110 111 #else /* STACK_DIRECTION == 0; need run-time code. */ 112 113 static int stack_dir; /* 1 or -1 once known. */ 114 #define STACK_DIR stack_dir 115 116 static void 117 find_stack_direction (void) 118 { 119 static char *addr = NULL; /* Address of first `dummy', once known. */ 120 auto char dummy; /* To get stack address. */ 121 122 if (addr == NULL) 123 { /* Initial entry. */ 124 addr = ADDRESS_FUNCTION (dummy); 125 126 find_stack_direction (); /* Recurse once. */ 127 } 128 else 129 { 130 /* Second entry. */ 131 if (ADDRESS_FUNCTION (dummy) > addr) 132 stack_dir = 1; /* Stack grew upward. */ 133 else 134 stack_dir = -1; /* Stack grew downward. */ 135 } 136 } 137 138 #endif /* STACK_DIRECTION == 0 */ 139 140 /* An "alloca header" is used to: 141 (a) chain together all alloca'ed blocks; 142 (b) keep track of stack depth. 143 144 It is very important that sizeof(header) agree with malloc 145 alignment chunk size. The following default should work okay. */ 146 147 #ifndef ALIGN_SIZE 148 #define ALIGN_SIZE sizeof(double) 149 #endif 150 151 typedef union hdr 152 { 153 char align[ALIGN_SIZE]; /* To force sizeof(header). */ 154 struct 155 { 156 union hdr *next; /* For chaining headers. */ 157 char *deep; /* For stack depth measure. */ 158 } h; 159 } header; 160 161 static header *last_alloca_header = NULL; /* -> last alloca header. */ 162 163 /* Return a pointer to at least SIZE bytes of storage, 164 which will be automatically reclaimed upon exit from 165 the procedure that called alloca. Originally, this space 166 was supposed to be taken from the current stack frame of the 167 caller, but that method cannot be made to work for some 168 implementations of C, for example under Gould's UTX/32. */ 169 170 pointer 171 alloca (unsigned size) 172 { 173 auto char probe; /* Probes stack depth: */ 174 register char *depth = ADDRESS_FUNCTION (probe); 175 176 #if STACK_DIRECTION == 0 177 if (STACK_DIR == 0) /* Unknown growth direction. */ 178 find_stack_direction (); 179 #endif 180 181 /* Reclaim garbage, defined as all alloca'd storage that 182 was allocated from deeper in the stack than currently. */ 183 184 { 185 register header *hp; /* Traverses linked list. */ 186 187 #ifdef emacs 188 BLOCK_INPUT; 189 #endif 190 191 for (hp = last_alloca_header; hp != NULL;) 192 if ((STACK_DIR > 0 && hp->h.deep > depth) 193 || (STACK_DIR < 0 && hp->h.deep < depth)) 194 { 195 register header *np = hp->h.next; 196 197 free ((pointer) hp); /* Collect garbage. */ 198 199 hp = np; /* -> next header. */ 200 } 201 else 202 break; /* Rest are not deeper. */ 203 204 last_alloca_header = hp; /* -> last valid storage. */ 205 206 #ifdef emacs 207 UNBLOCK_INPUT; 208 #endif 209 } 210 211 if (size == 0) 212 return NULL; /* No allocation required. */ 213 214 /* Allocate combined header + user data storage. */ 215 216 { 217 register pointer new = malloc (sizeof (header) + size); 218 /* Address of header. */ 219 220 if (new == 0) 221 abort(); 222 223 ((header *) new)->h.next = last_alloca_header; 224 ((header *) new)->h.deep = depth; 225 226 last_alloca_header = (header *) new; 227 228 /* User storage begins just after header. */ 229 230 return (pointer) ((char *) new + sizeof (header)); 231 } 232 } 233 234 #if defined (CRAY) && defined (CRAY_STACKSEG_END) 235 236 #ifdef DEBUG_I00AFUNC 237 #include <stdio.h> 238 #endif 239 240 #ifndef CRAY_STACK 241 #define CRAY_STACK 242 #ifndef CRAY2 243 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ 244 struct stack_control_header 245 { 246 long shgrow:32; /* Number of times stack has grown. */ 247 long shaseg:32; /* Size of increments to stack. */ 248 long shhwm:32; /* High water mark of stack. */ 249 long shsize:32; /* Current size of stack (all segments). */ 250 }; 251 252 /* The stack segment linkage control information occurs at 253 the high-address end of a stack segment. (The stack 254 grows from low addresses to high addresses.) The initial 255 part of the stack segment linkage control information is 256 0200 (octal) words. This provides for register storage 257 for the routine which overflows the stack. */ 258 259 struct stack_segment_linkage 260 { 261 long ss[0200]; /* 0200 overflow words. */ 262 long sssize:32; /* Number of words in this segment. */ 263 long ssbase:32; /* Offset to stack base. */ 264 long:32; 265 long sspseg:32; /* Offset to linkage control of previous 266 segment of stack. */ 267 long:32; 268 long sstcpt:32; /* Pointer to task common address block. */ 269 long sscsnm; /* Private control structure number for 270 microtasking. */ 271 long ssusr1; /* Reserved for user. */ 272 long ssusr2; /* Reserved for user. */ 273 long sstpid; /* Process ID for pid based multi-tasking. */ 274 long ssgvup; /* Pointer to multitasking thread giveup. */ 275 long sscray[7]; /* Reserved for Cray Research. */ 276 long ssa0; 277 long ssa1; 278 long ssa2; 279 long ssa3; 280 long ssa4; 281 long ssa5; 282 long ssa6; 283 long ssa7; 284 long sss0; 285 long sss1; 286 long sss2; 287 long sss3; 288 long sss4; 289 long sss5; 290 long sss6; 291 long sss7; 292 }; 293 294 #else /* CRAY2 */ 295 /* The following structure defines the vector of words 296 returned by the STKSTAT library routine. */ 297 struct stk_stat 298 { 299 long now; /* Current total stack size. */ 300 long maxc; /* Amount of contiguous space which would 301 be required to satisfy the maximum 302 stack demand to date. */ 303 long high_water; /* Stack high-water mark. */ 304 long overflows; /* Number of stack overflow ($STKOFEN) calls. */ 305 long hits; /* Number of internal buffer hits. */ 306 long extends; /* Number of block extensions. */ 307 long stko_mallocs; /* Block allocations by $STKOFEN. */ 308 long underflows; /* Number of stack underflow calls ($STKRETN). */ 309 long stko_free; /* Number of deallocations by $STKRETN. */ 310 long stkm_free; /* Number of deallocations by $STKMRET. */ 311 long segments; /* Current number of stack segments. */ 312 long maxs; /* Maximum number of stack segments so far. */ 313 long pad_size; /* Stack pad size. */ 314 long current_address; /* Current stack segment address. */ 315 long current_size; /* Current stack segment size. This 316 number is actually corrupted by STKSTAT to 317 include the fifteen word trailer area. */ 318 long initial_address; /* Address of initial segment. */ 319 long initial_size; /* Size of initial segment. */ 320 }; 321 322 /* The following structure describes the data structure which trails 323 any stack segment. I think that the description in 'asdef' is 324 out of date. I only describe the parts that I am sure about. */ 325 326 struct stk_trailer 327 { 328 long this_address; /* Address of this block. */ 329 long this_size; /* Size of this block (does not include 330 this trailer). */ 331 long unknown2; 332 long unknown3; 333 long link; /* Address of trailer block of previous 334 segment. */ 335 long unknown5; 336 long unknown6; 337 long unknown7; 338 long unknown8; 339 long unknown9; 340 long unknown10; 341 long unknown11; 342 long unknown12; 343 long unknown13; 344 long unknown14; 345 }; 346 347 #endif /* CRAY2 */ 348 #endif /* not CRAY_STACK */ 349 350 #ifdef CRAY2 351 /* Determine a "stack measure" for an arbitrary ADDRESS. 352 I doubt that "lint" will like this much. */ 353 354 static long 355 i00afunc (long *address) 356 { 357 struct stk_stat status; 358 struct stk_trailer *trailer; 359 long *block, size; 360 long result = 0; 361 362 /* We want to iterate through all of the segments. The first 363 step is to get the stack status structure. We could do this 364 more quickly and more directly, perhaps, by referencing the 365 $LM00 common block, but I know that this works. */ 366 367 STKSTAT (&status); 368 369 /* Set up the iteration. */ 370 371 trailer = (struct stk_trailer *) (status.current_address 372 + status.current_size 373 - 15); 374 375 /* There must be at least one stack segment. Therefore it is 376 a fatal error if "trailer" is null. */ 377 378 if (trailer == 0) 379 abort (); 380 381 /* Discard segments that do not contain our argument address. */ 382 383 while (trailer != 0) 384 { 385 block = (long *) trailer->this_address; 386 size = trailer->this_size; 387 if (block == 0 || size == 0) 388 abort (); 389 trailer = (struct stk_trailer *) trailer->link; 390 if ((block <= address) && (address < (block + size))) 391 break; 392 } 393 394 /* Set the result to the offset in this segment and add the sizes 395 of all predecessor segments. */ 396 397 result = address - block; 398 399 if (trailer == 0) 400 { 401 return result; 402 } 403 404 do 405 { 406 if (trailer->this_size <= 0) 407 abort (); 408 result += trailer->this_size; 409 trailer = (struct stk_trailer *) trailer->link; 410 } 411 while (trailer != 0); 412 413 /* We are done. Note that if you present a bogus address (one 414 not in any segment), you will get a different number back, formed 415 from subtracting the address of the first block. This is probably 416 not what you want. */ 417 418 return (result); 419 } 420 421 #else /* not CRAY2 */ 422 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. 423 Determine the number of the cell within the stack, 424 given the address of the cell. The purpose of this 425 routine is to linearize, in some sense, stack addresses 426 for alloca. */ 427 428 static long 429 i00afunc (long address) 430 { 431 long stkl = 0; 432 433 long size, pseg, this_segment, stack; 434 long result = 0; 435 436 struct stack_segment_linkage *ssptr; 437 438 /* Register B67 contains the address of the end of the 439 current stack segment. If you (as a subprogram) store 440 your registers on the stack and find that you are past 441 the contents of B67, you have overflowed the segment. 442 443 B67 also points to the stack segment linkage control 444 area, which is what we are really interested in. */ 445 446 stkl = CRAY_STACKSEG_END (); 447 ssptr = (struct stack_segment_linkage *) stkl; 448 449 /* If one subtracts 'size' from the end of the segment, 450 one has the address of the first word of the segment. 451 452 If this is not the first segment, 'pseg' will be 453 nonzero. */ 454 455 pseg = ssptr->sspseg; 456 size = ssptr->sssize; 457 458 this_segment = stkl - size; 459 460 /* It is possible that calling this routine itself caused 461 a stack overflow. Discard stack segments which do not 462 contain the target address. */ 463 464 while (!(this_segment <= address && address <= stkl)) 465 { 466 #ifdef DEBUG_I00AFUNC 467 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); 468 #endif 469 if (pseg == 0) 470 break; 471 stkl = stkl - pseg; 472 ssptr = (struct stack_segment_linkage *) stkl; 473 size = ssptr->sssize; 474 pseg = ssptr->sspseg; 475 this_segment = stkl - size; 476 } 477 478 result = address - this_segment; 479 480 /* If you subtract pseg from the current end of the stack, 481 you get the address of the previous stack segment's end. 482 This seems a little convoluted to me, but I'll bet you save 483 a cycle somewhere. */ 484 485 while (pseg != 0) 486 { 487 #ifdef DEBUG_I00AFUNC 488 fprintf (stderr, "%011o %011o\n", pseg, size); 489 #endif 490 stkl = stkl - pseg; 491 ssptr = (struct stack_segment_linkage *) stkl; 492 size = ssptr->sssize; 493 pseg = ssptr->sspseg; 494 result += size; 495 } 496 return (result); 497 } 498 499 #endif /* not CRAY2 */ 500 #endif /* CRAY */ 501 502 #endif /* no alloca */ 503 #endif /* not GCC version 2 */ 504
