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