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 void 97find_stack_direction (void) 98{ 99 static char *addr = NULL; /* Address of first `dummy', once known. */ 100 auto char dummy; /* To get stack address. */ 101 102 if (addr == NULL) 103 { /* Initial entry. */ 104 addr = ADDRESS_FUNCTION (dummy); 105 106 find_stack_direction (); /* Recurse once. */ 107 } 108 else 109 { 110 /* Second entry. */ 111 if (ADDRESS_FUNCTION (dummy) > addr) 112 stack_dir = 1; /* Stack grew upward. */ 113 else 114 stack_dir = -1; /* Stack grew downward. */ 115 } 116} 117 118# endif /* STACK_DIRECTION == 0 */ 119 120/* An "alloca header" is used to: 121 (a) chain together all alloca'ed blocks; 122 (b) keep track of stack depth. 123 124 It is very important that sizeof(header) agree with malloc 125 alignment chunk size. The following default should work okay. */ 126 127# ifndef ALIGN_SIZE 128# define ALIGN_SIZE sizeof(double) 129# endif 130 131typedef union hdr 132{ 133 char align[ALIGN_SIZE]; /* To force sizeof(header). */ 134 struct 135 { 136 union hdr *next; /* For chaining headers. */ 137 char *deep; /* For stack depth measure. */ 138 } h; 139} header; 140 141static header *last_alloca_header = NULL; /* -> last alloca header. */ 142 143/* Return a pointer to at least SIZE bytes of storage, 144 which will be automatically reclaimed upon exit from 145 the procedure that called alloca. Originally, this space 146 was supposed to be taken from the current stack frame of the 147 caller, but that method cannot be made to work for some 148 implementations of C, for example under Gould's UTX/32. */ 149 150void * 151alloca (size_t size) 152{ 153 auto char probe; /* Probes stack depth: */ 154 register char *depth = ADDRESS_FUNCTION (probe); 155 156# if STACK_DIRECTION == 0 157 if (STACK_DIR == 0) /* Unknown growth direction. */ 158 find_stack_direction (); 159# endif 160 161 /* Reclaim garbage, defined as all alloca'd storage that 162 was allocated from deeper in the stack than currently. */ 163 164 { 165 register header *hp; /* Traverses linked list. */ 166 167# ifdef emacs 168 BLOCK_INPUT; 169# endif 170 171 for (hp = last_alloca_header; hp != NULL;) 172 if ((STACK_DIR > 0 && hp->h.deep > depth) 173 || (STACK_DIR < 0 && hp->h.deep < depth)) 174 { 175 register header *np = hp->h.next; 176 177 free (hp); /* Collect garbage. */ 178 179 hp = np; /* -> next header. */ 180 } 181 else 182 break; /* Rest are not deeper. */ 183 184 last_alloca_header = hp; /* -> last valid storage. */ 185 186# ifdef emacs 187 UNBLOCK_INPUT; 188# endif 189 } 190 191 if (size == 0) 192 return NULL; /* No allocation required. */ 193 194 /* Allocate combined header + user data storage. */ 195 196 { 197 /* Address of header. */ 198 register header *new; 199 200 size_t combined_size = sizeof (header) + size; 201 if (combined_size < sizeof (header)) 202 memory_full (); 203 204 new = malloc (combined_size); 205 206 if (! new) 207 memory_full (); 208 209 new->h.next = last_alloca_header; 210 new->h.deep = depth; 211 212 last_alloca_header = new; 213 214 /* User storage begins just after header. */ 215 216 return (void *) (new + 1); 217 } 218} 219 220# if defined (CRAY) && defined (CRAY_STACKSEG_END) 221 222# ifdef DEBUG_I00AFUNC 223# include <stdio.h> 224# endif 225 226# ifndef CRAY_STACK 227# define CRAY_STACK 228# ifndef CRAY2 229/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ 230struct stack_control_header 231 { 232 long shgrow:32; /* Number of times stack has grown. */ 233 long shaseg:32; /* Size of increments to stack. */ 234 long shhwm:32; /* High water mark of stack. */ 235 long shsize:32; /* Current size of stack (all segments). */ 236 }; 237 238/* The stack segment linkage control information occurs at 239 the high-address end of a stack segment. (The stack 240 grows from low addresses to high addresses.) The initial 241 part of the stack segment linkage control information is 242 0200 (octal) words. This provides for register storage 243 for the routine which overflows the stack. */ 244 245struct stack_segment_linkage 246 { 247 long ss[0200]; /* 0200 overflow words. */ 248 long sssize:32; /* Number of words in this segment. */ 249 long ssbase:32; /* Offset to stack base. */ 250 long:32; 251 long sspseg:32; /* Offset to linkage control of previous 252 segment of stack. */ 253 long:32; 254 long sstcpt:32; /* Pointer to task common address block. */ 255 long sscsnm; /* Private control structure number for 256 microtasking. */ 257 long ssusr1; /* Reserved for user. */ 258 long ssusr2; /* Reserved for user. */ 259 long sstpid; /* Process ID for pid based multi-tasking. */ 260 long ssgvup; /* Pointer to multitasking thread giveup. */ 261 long sscray[7]; /* Reserved for Cray Research. */ 262 long ssa0; 263 long ssa1; 264 long ssa2; 265 long ssa3; 266 long ssa4; 267 long ssa5; 268 long ssa6; 269 long ssa7; 270 long sss0; 271 long sss1; 272 long sss2; 273 long sss3; 274 long sss4; 275 long sss5; 276 long sss6; 277 long sss7; 278 }; 279 280# else /* CRAY2 */ 281/* The following structure defines the vector of words 282 returned by the STKSTAT library routine. */ 283struct stk_stat 284 { 285 long now; /* Current total stack size. */ 286 long maxc; /* Amount of contiguous space which would 287 be required to satisfy the maximum 288 stack demand to date. */ 289 long high_water; /* Stack high-water mark. */ 290 long overflows; /* Number of stack overflow ($STKOFEN) calls. */ 291 long hits; /* Number of internal buffer hits. */ 292 long extends; /* Number of block extensions. */ 293 long stko_mallocs; /* Block allocations by $STKOFEN. */ 294 long underflows; /* Number of stack underflow calls ($STKRETN). */ 295 long stko_free; /* Number of deallocations by $STKRETN. */ 296 long stkm_free; /* Number of deallocations by $STKMRET. */ 297 long segments; /* Current number of stack segments. */ 298 long maxs; /* Maximum number of stack segments so far. */ 299 long pad_size; /* Stack pad size. */ 300 long current_address; /* Current stack segment address. */ 301 long current_size; /* Current stack segment size. This 302 number is actually corrupted by STKSTAT to 303 include the fifteen word trailer area. */ 304 long initial_address; /* Address of initial segment. */ 305 long initial_size; /* Size of initial segment. */ 306 }; 307 308/* The following structure describes the data structure which trails 309 any stack segment. I think that the description in 'asdef' is 310 out of date. I only describe the parts that I am sure about. */ 311 312struct stk_trailer 313 { 314 long this_address; /* Address of this block. */ 315 long this_size; /* Size of this block (does not include 316 this trailer). */ 317 long unknown2; 318 long unknown3; 319 long link; /* Address of trailer block of previous 320 segment. */ 321 long unknown5; 322 long unknown6; 323 long unknown7; 324 long unknown8; 325 long unknown9; 326 long unknown10; 327 long unknown11; 328 long unknown12; 329 long unknown13; 330 long unknown14; 331 }; 332 333# endif /* CRAY2 */ 334# endif /* not CRAY_STACK */ 335 336# ifdef CRAY2 337/* Determine a "stack measure" for an arbitrary ADDRESS. 338 I doubt that "lint" will like this much. */ 339 340static long 341i00afunc (long *address) 342{ 343 struct stk_stat status; 344 struct stk_trailer *trailer; 345 long *block, size; 346 long result = 0; 347 348 /* We want to iterate through all of the segments. The first 349 step is to get the stack status structure. We could do this 350 more quickly and more directly, perhaps, by referencing the 351 $LM00 common block, but I know that this works. */ 352 353 STKSTAT (&status); 354 355 /* Set up the iteration. */ 356 357 trailer = (struct stk_trailer *) (status.current_address 358 + status.current_size 359 - 15); 360 361 /* There must be at least one stack segment. Therefore it is 362 a fatal error if "trailer" is null. */ 363 364 if (trailer == 0) 365 abort (); 366 367 /* Discard segments that do not contain our argument address. */ 368 369 while (trailer != 0) 370 { 371 block = (long *) trailer->this_address; 372 size = trailer->this_size; 373 if (block == 0 || size == 0) 374 abort (); 375 trailer = (struct stk_trailer *) trailer->link; 376 if ((block <= address) && (address < (block + size))) 377 break; 378 } 379 380 /* Set the result to the offset in this segment and add the sizes 381 of all predecessor segments. */ 382 383 result = address - block; 384 385 if (trailer == 0) 386 { 387 return result; 388 } 389 390 do 391 { 392 if (trailer->this_size <= 0) 393 abort (); 394 result += trailer->this_size; 395 trailer = (struct stk_trailer *) trailer->link; 396 } 397 while (trailer != 0); 398 399 /* We are done. Note that if you present a bogus address (one 400 not in any segment), you will get a different number back, formed 401 from subtracting the address of the first block. This is probably 402 not what you want. */ 403 404 return (result); 405} 406 407# else /* not CRAY2 */ 408/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. 409 Determine the number of the cell within the stack, 410 given the address of the cell. The purpose of this 411 routine is to linearize, in some sense, stack addresses 412 for alloca. */ 413 414static long 415i00afunc (long address) 416{ 417 long stkl = 0; 418 419 long size, pseg, this_segment, stack; 420 long result = 0; 421 422 struct stack_segment_linkage *ssptr; 423 424 /* Register B67 contains the address of the end of the 425 current stack segment. If you (as a subprogram) store 426 your registers on the stack and find that you are past 427 the contents of B67, you have overflowed the segment. 428 429 B67 also points to the stack segment linkage control 430 area, which is what we are really interested in. */ 431 432 stkl = CRAY_STACKSEG_END (); 433 ssptr = (struct stack_segment_linkage *) stkl; 434 435 /* If one subtracts 'size' from the end of the segment, 436 one has the address of the first word of the segment. 437 438 If this is not the first segment, 'pseg' will be 439 nonzero. */ 440 441 pseg = ssptr->sspseg; 442 size = ssptr->sssize; 443 444 this_segment = stkl - size; 445 446 /* It is possible that calling this routine itself caused 447 a stack overflow. Discard stack segments which do not 448 contain the target address. */ 449 450 while (!(this_segment <= address && address <= stkl)) 451 { 452# ifdef DEBUG_I00AFUNC 453 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); 454# endif 455 if (pseg == 0) 456 break; 457 stkl = stkl - pseg; 458 ssptr = (struct stack_segment_linkage *) stkl; 459 size = ssptr->sssize; 460 pseg = ssptr->sspseg; 461 this_segment = stkl - size; 462 } 463 464 result = address - this_segment; 465 466 /* If you subtract pseg from the current end of the stack, 467 you get the address of the previous stack segment's end. 468 This seems a little convoluted to me, but I'll bet you save 469 a cycle somewhere. */ 470 471 while (pseg != 0) 472 { 473# ifdef DEBUG_I00AFUNC 474 fprintf (stderr, "%011o %011o\n", pseg, size); 475# endif 476 stkl = stkl - pseg; 477 ssptr = (struct stack_segment_linkage *) stkl; 478 size = ssptr->sssize; 479 pseg = ssptr->sspseg; 480 result += size; 481 } 482 return (result); 483} 484 485# endif /* not CRAY2 */ 486# endif /* CRAY */ 487 488# endif /* no alloca */ 489#endif /* not GCC version 3 */ 490