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@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/* If compiling with GCC 2, this file's not needed. */ 29#if !defined (__GNUC__) || __GNUC__ < 2 30 31#include <bashtypes.h> /* for size_t */ 32 33/* If alloca is defined somewhere, this file is not needed. */ 34#ifndef alloca 35 36#ifdef emacs 37#ifdef static 38/* actually, only want this if static is defined as "" 39 -- this is for usg, in which emacs must undefine static 40 in order to make unexec workable 41 */ 42#ifndef STACK_DIRECTION 43you 44lose 45-- must know STACK_DIRECTION at compile-time 46#endif /* STACK_DIRECTION undefined */ 47#endif /* static */ 48#endif /* emacs */ 49 50/* If your stack is a linked list of frames, you have to 51 provide an "address metric" ADDRESS_FUNCTION macro. */ 52 53#if defined (CRAY) && defined (CRAY_STACKSEG_END) 54long i00afunc (); 55#define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) 56#else 57#define ADDRESS_FUNCTION(arg) &(arg) 58#endif /* CRAY && CRAY_STACKSEG_END */ 59 60#if __STDC__ 61typedef void *pointer; 62#else 63typedef char *pointer; 64#endif 65 66#define NULL 0 67 68/* Different portions of Emacs need to call different versions of 69 malloc. The Emacs executable needs alloca to call xmalloc, because 70 ordinary malloc isn't protected from input signals. On the other 71 hand, the utilities in lib-src need alloca to call malloc; some of 72 them are very simple, and don't have an xmalloc routine. 73 74 Non-Emacs programs expect this to call use xmalloc. 75 76 Callers below should use malloc. */ 77 78#ifndef emacs 79#define malloc xmalloc 80extern pointer xmalloc (); 81#endif 82 83/* Define STACK_DIRECTION if you know the direction of stack 84 growth for your system; otherwise it will be automatically 85 deduced at run-time. 86 87 STACK_DIRECTION > 0 => grows toward higher addresses 88 STACK_DIRECTION < 0 => grows toward lower addresses 89 STACK_DIRECTION = 0 => direction of growth unknown */ 90 91#ifndef STACK_DIRECTION 92#define STACK_DIRECTION 0 /* Direction unknown. */ 93#endif 94 95#if STACK_DIRECTION != 0 96 97#define STACK_DIR STACK_DIRECTION /* Known at compile-time. */ 98 99#else /* STACK_DIRECTION == 0; need run-time code. */ 100 101static int stack_dir; /* 1 or -1 once known. */ 102#define STACK_DIR stack_dir 103 104static void 105find_stack_direction () 106{ 107 static char *addr = NULL; /* Address of first `dummy', once known. */ 108 auto char dummy; /* To get stack address. */ 109 110 if (addr == NULL) 111 { /* Initial entry. */ 112 addr = ADDRESS_FUNCTION (dummy); 113 114 find_stack_direction (); /* Recurse once. */ 115 } 116 else 117 { 118 /* Second entry. */ 119 if (ADDRESS_FUNCTION (dummy) > addr) 120 stack_dir = 1; /* Stack grew upward. */ 121 else 122 stack_dir = -1; /* Stack grew downward. */ 123 } 124} 125 126#endif /* STACK_DIRECTION == 0 */ 127 128/* An "alloca header" is used to: 129 (a) chain together all alloca'ed blocks; 130 (b) keep track of stack depth. 131 132 It is very important that sizeof(header) agree with malloc 133 alignment chunk size. The following default should work okay. */ 134 135#ifndef ALIGN_SIZE 136#define ALIGN_SIZE sizeof(double) 137#endif 138 139typedef union hdr 140{ 141 char align[ALIGN_SIZE]; /* To force sizeof(header). */ 142 struct 143 { 144 union hdr *next; /* For chaining headers. */ 145 char *deep; /* For stack depth measure. */ 146 } h; 147} header; 148 149static header *last_alloca_header = NULL; /* -> last alloca header. */ 150 151/* Return a pointer to at least SIZE bytes of storage, 152 which will be automatically reclaimed upon exit from 153 the procedure that called alloca. Originally, this space 154 was supposed to be taken from the current stack frame of the 155 caller, but that method cannot be made to work for some 156 implementations of C, for example under Gould's UTX/32. */ 157 158pointer 159alloca (size) 160 size_t size; 161{ 162 auto char probe; /* Probes stack depth: */ 163 register char *depth = ADDRESS_FUNCTION (probe); 164 165#if STACK_DIRECTION == 0 166 if (STACK_DIR == 0) /* Unknown growth direction. */ 167 find_stack_direction (); 168#endif 169 170 /* Reclaim garbage, defined as all alloca'd storage that 171 was allocated from deeper in the stack than currently. */ 172 173 { 174 register header *hp; /* Traverses linked list. */ 175 176 for (hp = last_alloca_header; hp != NULL;) 177 if ((STACK_DIR > 0 && hp->h.deep > depth) 178 || (STACK_DIR < 0 && hp->h.deep < depth)) 179 { 180 register header *np = hp->h.next; 181 182 free ((pointer) hp); /* Collect garbage. */ 183 184 hp = np; /* -> next header. */ 185 } 186 else 187 break; /* Rest are not deeper. */ 188 189 last_alloca_header = hp; /* -> last valid storage. */ 190 } 191 192 if (size == 0) 193 return NULL; /* No allocation required. */ 194 195 /* Allocate combined header + user data storage. */ 196 197 { 198 register pointer new = malloc (sizeof (header) + size); 199 /* Address of header. */ 200 201 ((header *) new)->h.next = last_alloca_header; 202 ((header *) new)->h.deep = depth; 203 204 last_alloca_header = (header *) new; 205 206 /* User storage begins just after header. */ 207 208 return (pointer) ((char *) new + sizeof (header)); 209 } 210} 211 212#if defined (CRAY) && defined (CRAY_STACKSEG_END) 213 214#ifdef DEBUG_I00AFUNC 215#include <stdio.h> 216#endif 217 218#ifndef CRAY_STACK 219#define CRAY_STACK 220#ifndef CRAY2 221/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ 222struct stack_control_header 223 { 224 long shgrow:32; /* Number of times stack has grown. */ 225 long shaseg:32; /* Size of increments to stack. */ 226 long shhwm:32; /* High water mark of stack. */ 227 long shsize:32; /* Current size of stack (all segments). */ 228 }; 229 230/* The stack segment linkage control information occurs at 231 the high-address end of a stack segment. (The stack 232 grows from low addresses to high addresses.) The initial 233 part of the stack segment linkage control information is 234 0200 (octal) words. This provides for register storage 235 for the routine which overflows the stack. */ 236 237struct stack_segment_linkage 238 { 239 long ss[0200]; /* 0200 overflow words. */ 240 long sssize:32; /* Number of words in this segment. */ 241 long ssbase:32; /* Offset to stack base. */ 242 long:32; 243 long sspseg:32; /* Offset to linkage control of previous 244 segment of stack. */ 245 long:32; 246 long sstcpt:32; /* Pointer to task common address block. */ 247 long sscsnm; /* Private control structure number for 248 microtasking. */ 249 long ssusr1; /* Reserved for user. */ 250 long ssusr2; /* Reserved for user. */ 251 long sstpid; /* Process ID for pid based multi-tasking. */ 252 long ssgvup; /* Pointer to multitasking thread giveup. */ 253 long sscray[7]; /* Reserved for Cray Research. */ 254 long ssa0; 255 long ssa1; 256 long ssa2; 257 long ssa3; 258 long ssa4; 259 long ssa5; 260 long ssa6; 261 long ssa7; 262 long sss0; 263 long sss1; 264 long sss2; 265 long sss3; 266 long sss4; 267 long sss5; 268 long sss6; 269 long sss7; 270 }; 271 272#else /* CRAY2 */ 273/* The following structure defines the vector of words 274 returned by the STKSTAT library routine. */ 275struct stk_stat 276 { 277 long now; /* Current total stack size. */ 278 long maxc; /* Amount of contiguous space which would 279 be required to satisfy the maximum 280 stack demand to date. */ 281 long high_water; /* Stack high-water mark. */ 282 long overflows; /* Number of stack overflow ($STKOFEN) calls. */ 283 long hits; /* Number of internal buffer hits. */ 284 long extends; /* Number of block extensions. */ 285 long stko_mallocs; /* Block allocations by $STKOFEN. */ 286 long underflows; /* Number of stack underflow calls ($STKRETN). */ 287 long stko_free; /* Number of deallocations by $STKRETN. */ 288 long stkm_free; /* Number of deallocations by $STKMRET. */ 289 long segments; /* Current number of stack segments. */ 290 long maxs; /* Maximum number of stack segments so far. */ 291 long pad_size; /* Stack pad size. */ 292 long current_address; /* Current stack segment address. */ 293 long current_size; /* Current stack segment size. This 294 number is actually corrupted by STKSTAT to 295 include the fifteen word trailer area. */ 296 long initial_address; /* Address of initial segment. */ 297 long initial_size; /* Size of initial segment. */ 298 }; 299 300/* The following structure describes the data structure which trails 301 any stack segment. I think that the description in 'asdef' is 302 out of date. I only describe the parts that I am sure about. */ 303 304struct stk_trailer 305 { 306 long this_address; /* Address of this block. */ 307 long this_size; /* Size of this block (does not include 308 this trailer). */ 309 long unknown2; 310 long unknown3; 311 long link; /* Address of trailer block of previous 312 segment. */ 313 long unknown5; 314 long unknown6; 315 long unknown7; 316 long unknown8; 317 long unknown9; 318 long unknown10; 319 long unknown11; 320 long unknown12; 321 long unknown13; 322 long unknown14; 323 }; 324 325#endif /* CRAY2 */ 326#endif /* not CRAY_STACK */ 327 328#ifdef CRAY2 329/* Determine a "stack measure" for an arbitrary ADDRESS. 330 I doubt that "lint" will like this much. */ 331 332static long 333i00afunc (long *address) 334{ 335 struct stk_stat status; 336 struct stk_trailer *trailer; 337 long *block, size; 338 long result = 0; 339 340 /* We want to iterate through all of the segments. The first 341 step is to get the stack status structure. We could do this 342 more quickly and more directly, perhaps, by referencing the 343 $LM00 common block, but I know that this works. */ 344 345 STKSTAT (&status); 346 347 /* Set up the iteration. */ 348 349 trailer = (struct stk_trailer *) (status.current_address 350 + status.current_size 351 - 15); 352 353 /* There must be at least one stack segment. Therefore it is 354 a fatal error if "trailer" is null. */ 355 356 if (trailer == 0) 357 abort (); 358 359 /* Discard segments that do not contain our argument address. */ 360 361 while (trailer != 0) 362 { 363 block = (long *) trailer->this_address; 364 size = trailer->this_size; 365 if (block == 0 || size == 0) 366 abort (); 367 trailer = (struct stk_trailer *) trailer->link; 368 if ((block <= address) && (address < (block + size))) 369 break; 370 } 371 372 /* Set the result to the offset in this segment and add the sizes 373 of all predecessor segments. */ 374 375 result = address - block; 376 377 if (trailer == 0) 378 { 379 return result; 380 } 381 382 do 383 { 384 if (trailer->this_size <= 0) 385 abort (); 386 result += trailer->this_size; 387 trailer = (struct stk_trailer *) trailer->link; 388 } 389 while (trailer != 0); 390 391 /* We are done. Note that if you present a bogus address (one 392 not in any segment), you will get a different number back, formed 393 from subtracting the address of the first block. This is probably 394 not what you want. */ 395 396 return (result); 397} 398 399#else /* not CRAY2 */ 400/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. 401 Determine the number of the cell within the stack, 402 given the address of the cell. The purpose of this 403 routine is to linearize, in some sense, stack addresses 404 for alloca. */ 405 406static long 407i00afunc (long address) 408{ 409 long stkl = 0; 410 411 long size, pseg, this_segment, stack; 412 long result = 0; 413 414 struct stack_segment_linkage *ssptr; 415 416 /* Register B67 contains the address of the end of the 417 current stack segment. If you (as a subprogram) store 418 your registers on the stack and find that you are past 419 the contents of B67, you have overflowed the segment. 420 421 B67 also points to the stack segment linkage control 422 area, which is what we are really interested in. */ 423 424 /* This might be _getb67() or GETB67 () or getb67 () */ 425 stkl = CRAY_STACKSEG_END (); 426 ssptr = (struct stack_segment_linkage *) stkl; 427 428 /* If one subtracts 'size' from the end of the segment, 429 one has the address of the first word of the segment. 430 431 If this is not the first segment, 'pseg' will be 432 nonzero. */ 433 434 pseg = ssptr->sspseg; 435 size = ssptr->sssize; 436 437 this_segment = stkl - size; 438 439 /* It is possible that calling this routine itself caused 440 a stack overflow. Discard stack segments which do not 441 contain the target address. */ 442 443 while (!(this_segment <= address && address <= stkl)) 444 { 445#ifdef DEBUG_I00AFUNC 446 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); 447#endif 448 if (pseg == 0) 449 break; 450 stkl = stkl - pseg; 451 ssptr = (struct stack_segment_linkage *) stkl; 452 size = ssptr->sssize; 453 pseg = ssptr->sspseg; 454 this_segment = stkl - size; 455 } 456 457 result = address - this_segment; 458 459 /* If you subtract pseg from the current end of the stack, 460 you get the address of the previous stack segment's end. 461 This seems a little convoluted to me, but I'll bet you save 462 a cycle somewhere. */ 463 464 while (pseg != 0) 465 { 466#ifdef DEBUG_I00AFUNC 467 fprintf (stderr, "%011o %011o\n", pseg, size); 468#endif 469 stkl = stkl - pseg; 470 ssptr = (struct stack_segment_linkage *) stkl; 471 size = ssptr->sssize; 472 pseg = ssptr->sspseg; 473 result += size; 474 } 475 return (result); 476} 477 478#endif /* not CRAY2 */ 479#endif /* CRAY && CRAY_STACKSEG_END */ 480 481#endif /* no alloca */ 482#endif /* !__GNUC__ || __GNUC__ < 2 */ 483