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