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 HAVE_STRING_H 29# include <string.h> 30#endif 31#if 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 53you 54lose 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) 64long i00afunc (); 65# define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) 66# else 67# define ADDRESS_FUNCTION(arg) &(arg) 68# endif 69 70# if __STDC__ 71typedef void *pointer; 72# else 73typedef 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 xmalloc. 87 88 Callers below should use malloc. */ 89 90# ifndef emacs 91# undef malloc 92# define malloc xmalloc 93# endif 94extern pointer malloc (); 95 96/* Define STACK_DIRECTION if you know the direction of stack 97 growth for your system; otherwise it will be automatically 98 deduced at run-time. 99 100 STACK_DIRECTION > 0 => grows toward higher addresses 101 STACK_DIRECTION < 0 => grows toward lower addresses 102 STACK_DIRECTION = 0 => direction of growth unknown */ 103 104# ifndef STACK_DIRECTION 105# define STACK_DIRECTION 0 /* Direction unknown. */ 106# endif 107 108# if STACK_DIRECTION != 0 109 110# define STACK_DIR STACK_DIRECTION /* Known at compile-time. */ 111 112# else /* STACK_DIRECTION == 0; need run-time code. */ 113 114static int stack_dir; /* 1 or -1 once known. */ 115# define STACK_DIR stack_dir 116 117static void 118find_stack_direction () 119{ 120 static char *addr = NULL; /* Address of first `dummy', once known. */ 121 auto char dummy; /* To get stack address. */ 122 123 if (addr == NULL) 124 { /* Initial entry. */ 125 addr = ADDRESS_FUNCTION (dummy); 126 127 find_stack_direction (); /* Recurse once. */ 128 } 129 else 130 { 131 /* Second entry. */ 132 if (ADDRESS_FUNCTION (dummy) > addr) 133 stack_dir = 1; /* Stack grew upward. */ 134 else 135 stack_dir = -1; /* Stack grew downward. */ 136 } 137} 138 139# endif /* STACK_DIRECTION == 0 */ 140 141/* An "alloca header" is used to: 142 (a) chain together all alloca'ed blocks; 143 (b) keep track of stack depth. 144 145 It is very important that sizeof(header) agree with malloc 146 alignment chunk size. The following default should work okay. */ 147 148# ifndef ALIGN_SIZE 149# define ALIGN_SIZE sizeof(double) 150# endif 151 152typedef union hdr 153{ 154 char align[ALIGN_SIZE]; /* To force sizeof(header). */ 155 struct 156 { 157 union hdr *next; /* For chaining headers. */ 158 char *deep; /* For stack depth measure. */ 159 } h; 160} header; 161 162static header *last_alloca_header = NULL; /* -> last alloca header. */ 163 164/* Return a pointer to at least SIZE bytes of storage, 165 which will be automatically reclaimed upon exit from 166 the procedure that called alloca. Originally, this space 167 was supposed to be taken from the current stack frame of the 168 caller, but that method cannot be made to work for some 169 implementations of C, for example under Gould's UTX/32. */ 170 171pointer 172alloca (size_t size) 173{ 174 auto char probe; /* Probes stack depth: */ 175 register char *depth = ADDRESS_FUNCTION (probe); 176 177# if STACK_DIRECTION == 0 178 if (STACK_DIR == 0) /* Unknown growth direction. */ 179 find_stack_direction (); 180# endif 181 182 /* Reclaim garbage, defined as all alloca'd storage that 183 was allocated from deeper in the stack than currently. */ 184 185 { 186 register header *hp; /* Traverses linked list. */ 187 188# ifdef emacs 189 BLOCK_INPUT; 190# endif 191 192 for (hp = last_alloca_header; hp != NULL;) 193 if ((STACK_DIR > 0 && hp->h.deep > depth) 194 || (STACK_DIR < 0 && hp->h.deep < depth)) 195 { 196 register header *np = hp->h.next; 197 198 free ((pointer) hp); /* Collect garbage. */ 199 200 hp = np; /* -> next header. */ 201 } 202 else 203 break; /* Rest are not deeper. */ 204 205 last_alloca_header = hp; /* -> last valid storage. */ 206 207# ifdef emacs 208 UNBLOCK_INPUT; 209# endif 210 } 211 212 if (size == 0) 213 return NULL; /* No allocation required. */ 214 215 /* Allocate combined header + user data storage. */ 216 217 { 218 register pointer new = malloc (sizeof (header) + size); 219 /* Address of header. */ 220 221 if (new == 0) 222 abort(); 223 224 ((header *) new)->h.next = last_alloca_header; 225 ((header *) new)->h.deep = depth; 226 227 last_alloca_header = (header *) new; 228 229 /* User storage begins just after header. */ 230 231 return (pointer) ((char *) new + sizeof (header)); 232 } 233} 234 235# if defined (CRAY) && defined (CRAY_STACKSEG_END) 236 237# ifdef DEBUG_I00AFUNC 238# include <stdio.h> 239# endif 240 241# ifndef CRAY_STACK 242# define CRAY_STACK 243# ifndef CRAY2 244/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ 245struct stack_control_header 246 { 247 long shgrow:32; /* Number of times stack has grown. */ 248 long shaseg:32; /* Size of increments to stack. */ 249 long shhwm:32; /* High water mark of stack. */ 250 long shsize:32; /* Current size of stack (all segments). */ 251 }; 252 253/* The stack segment linkage control information occurs at 254 the high-address end of a stack segment. (The stack 255 grows from low addresses to high addresses.) The initial 256 part of the stack segment linkage control information is 257 0200 (octal) words. This provides for register storage 258 for the routine which overflows the stack. */ 259 260struct stack_segment_linkage 261 { 262 long ss[0200]; /* 0200 overflow words. */ 263 long sssize:32; /* Number of words in this segment. */ 264 long ssbase:32; /* Offset to stack base. */ 265 long:32; 266 long sspseg:32; /* Offset to linkage control of previous 267 segment of stack. */ 268 long:32; 269 long sstcpt:32; /* Pointer to task common address block. */ 270 long sscsnm; /* Private control structure number for 271 microtasking. */ 272 long ssusr1; /* Reserved for user. */ 273 long ssusr2; /* Reserved for user. */ 274 long sstpid; /* Process ID for pid based multi-tasking. */ 275 long ssgvup; /* Pointer to multitasking thread giveup. */ 276 long sscray[7]; /* Reserved for Cray Research. */ 277 long ssa0; 278 long ssa1; 279 long ssa2; 280 long ssa3; 281 long ssa4; 282 long ssa5; 283 long ssa6; 284 long ssa7; 285 long sss0; 286 long sss1; 287 long sss2; 288 long sss3; 289 long sss4; 290 long sss5; 291 long sss6; 292 long sss7; 293 }; 294 295# else /* CRAY2 */ 296/* The following structure defines the vector of words 297 returned by the STKSTAT library routine. */ 298struct stk_stat 299 { 300 long now; /* Current total stack size. */ 301 long maxc; /* Amount of contiguous space which would 302 be required to satisfy the maximum 303 stack demand to date. */ 304 long high_water; /* Stack high-water mark. */ 305 long overflows; /* Number of stack overflow ($STKOFEN) calls. */ 306 long hits; /* Number of internal buffer hits. */ 307 long extends; /* Number of block extensions. */ 308 long stko_mallocs; /* Block allocations by $STKOFEN. */ 309 long underflows; /* Number of stack underflow calls ($STKRETN). */ 310 long stko_free; /* Number of deallocations by $STKRETN. */ 311 long stkm_free; /* Number of deallocations by $STKMRET. */ 312 long segments; /* Current number of stack segments. */ 313 long maxs; /* Maximum number of stack segments so far. */ 314 long pad_size; /* Stack pad size. */ 315 long current_address; /* Current stack segment address. */ 316 long current_size; /* Current stack segment size. This 317 number is actually corrupted by STKSTAT to 318 include the fifteen word trailer area. */ 319 long initial_address; /* Address of initial segment. */ 320 long initial_size; /* Size of initial segment. */ 321 }; 322 323/* The following structure describes the data structure which trails 324 any stack segment. I think that the description in 'asdef' is 325 out of date. I only describe the parts that I am sure about. */ 326 327struct stk_trailer 328 { 329 long this_address; /* Address of this block. */ 330 long this_size; /* Size of this block (does not include 331 this trailer). */ 332 long unknown2; 333 long unknown3; 334 long link; /* Address of trailer block of previous 335 segment. */ 336 long unknown5; 337 long unknown6; 338 long unknown7; 339 long unknown8; 340 long unknown9; 341 long unknown10; 342 long unknown11; 343 long unknown12; 344 long unknown13; 345 long unknown14; 346 }; 347 348# endif /* CRAY2 */ 349# endif /* not CRAY_STACK */ 350 351# ifdef CRAY2 352/* Determine a "stack measure" for an arbitrary ADDRESS. 353 I doubt that "lint" will like this much. */ 354 355static long 356i00afunc (long *address) 357{ 358 struct stk_stat status; 359 struct stk_trailer *trailer; 360 long *block, size; 361 long result = 0; 362 363 /* We want to iterate through all of the segments. The first 364 step is to get the stack status structure. We could do this 365 more quickly and more directly, perhaps, by referencing the 366 $LM00 common block, but I know that this works. */ 367 368 STKSTAT (&status); 369 370 /* Set up the iteration. */ 371 372 trailer = (struct stk_trailer *) (status.current_address 373 + status.current_size 374 - 15); 375 376 /* There must be at least one stack segment. Therefore it is 377 a fatal error if "trailer" is null. */ 378 379 if (trailer == 0) 380 abort (); 381 382 /* Discard segments that do not contain our argument address. */ 383 384 while (trailer != 0) 385 { 386 block = (long *) trailer->this_address; 387 size = trailer->this_size; 388 if (block == 0 || size == 0) 389 abort (); 390 trailer = (struct stk_trailer *) trailer->link; 391 if ((block <= address) && (address < (block + size))) 392 break; 393 } 394 395 /* Set the result to the offset in this segment and add the sizes 396 of all predecessor segments. */ 397 398 result = address - block; 399 400 if (trailer == 0) 401 { 402 return result; 403 } 404 405 do 406 { 407 if (trailer->this_size <= 0) 408 abort (); 409 result += trailer->this_size; 410 trailer = (struct stk_trailer *) trailer->link; 411 } 412 while (trailer != 0); 413 414 /* We are done. Note that if you present a bogus address (one 415 not in any segment), you will get a different number back, formed 416 from subtracting the address of the first block. This is probably 417 not what you want. */ 418 419 return (result); 420} 421 422# else /* not CRAY2 */ 423/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. 424 Determine the number of the cell within the stack, 425 given the address of the cell. The purpose of this 426 routine is to linearize, in some sense, stack addresses 427 for alloca. */ 428 429static long 430i00afunc (long address) 431{ 432 long stkl = 0; 433 434 long size, pseg, this_segment, stack; 435 long result = 0; 436 437 struct stack_segment_linkage *ssptr; 438 439 /* Register B67 contains the address of the end of the 440 current stack segment. If you (as a subprogram) store 441 your registers on the stack and find that you are past 442 the contents of B67, you have overflowed the segment. 443 444 B67 also points to the stack segment linkage control 445 area, which is what we are really interested in. */ 446 447 stkl = CRAY_STACKSEG_END (); 448 ssptr = (struct stack_segment_linkage *) stkl; 449 450 /* If one subtracts 'size' from the end of the segment, 451 one has the address of the first word of the segment. 452 453 If this is not the first segment, 'pseg' will be 454 nonzero. */ 455 456 pseg = ssptr->sspseg; 457 size = ssptr->sssize; 458 459 this_segment = stkl - size; 460 461 /* It is possible that calling this routine itself caused 462 a stack overflow. Discard stack segments which do not 463 contain the target address. */ 464 465 while (!(this_segment <= address && address <= stkl)) 466 { 467# ifdef DEBUG_I00AFUNC 468 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); 469# endif 470 if (pseg == 0) 471 break; 472 stkl = stkl - pseg; 473 ssptr = (struct stack_segment_linkage *) stkl; 474 size = ssptr->sssize; 475 pseg = ssptr->sspseg; 476 this_segment = stkl - size; 477 } 478 479 result = address - this_segment; 480 481 /* If you subtract pseg from the current end of the stack, 482 you get the address of the previous stack segment's end. 483 This seems a little convoluted to me, but I'll bet you save 484 a cycle somewhere. */ 485 486 while (pseg != 0) 487 { 488# ifdef DEBUG_I00AFUNC 489 fprintf (stderr, "%011o %011o\n", pseg, size); 490# endif 491 stkl = stkl - pseg; 492 ssptr = (struct stack_segment_linkage *) stkl; 493 size = ssptr->sssize; 494 pseg = ssptr->sspseg; 495 result += size; 496 } 497 return (result); 498} 499 500# endif /* not CRAY2 */ 501# endif /* CRAY */ 502 503# endif /* no alloca */ 504#endif /* not GCC version 2 */ 505