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 #include <sys/cdefs.h> 24 __RCSID("$NetBSD: alloca.c,v 1.2 2016/05/17 14:00:09 christos Exp $"); 25 26 #ifdef HAVE_CONFIG_H 27 # include <config.h> 28 #endif 29 30 #include <alloca.h> 31 32 #include <string.h> 33 #include <stdlib.h> 34 35 #ifdef emacs 36 # include "lisp.h" 37 # include "blockinput.h" 38 # ifdef EMACS_FREE 39 # undef free 40 # define free EMACS_FREE 41 # endif 42 #else 43 # define memory_full() abort () 44 #endif 45 46 /* If compiling with GCC 2, this file's not needed. */ 47 #if !defined (__GNUC__) || __GNUC__ < 2 48 49 /* If someone has defined alloca as a macro, 50 there must be some other way alloca is supposed to work. */ 51 # ifndef alloca 52 53 # ifdef emacs 54 # ifdef static 55 /* actually, only want this if static is defined as "" 56 -- this is for usg, in which emacs must undefine static 57 in order to make unexec workable 58 */ 59 # ifndef STACK_DIRECTION 60 you 61 lose 62 -- must know STACK_DIRECTION at compile-time 63 /* Using #error here is not wise since this file should work for 64 old and obscure compilers. */ 65 # endif /* STACK_DIRECTION undefined */ 66 # endif /* static */ 67 # endif /* emacs */ 68 69 /* If your stack is a linked list of frames, you have to 70 provide an "address metric" ADDRESS_FUNCTION macro. */ 71 72 # if defined (CRAY) && defined (CRAY_STACKSEG_END) 73 long i00afunc (); 74 # define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) 75 # else 76 # define ADDRESS_FUNCTION(arg) &(arg) 77 # endif 78 79 /* Define STACK_DIRECTION if you know the direction of stack 80 growth for your system; otherwise it will be automatically 81 deduced at run-time. 82 83 STACK_DIRECTION > 0 => grows toward higher addresses 84 STACK_DIRECTION < 0 => grows toward lower addresses 85 STACK_DIRECTION = 0 => direction of growth unknown */ 86 87 # ifndef STACK_DIRECTION 88 # define STACK_DIRECTION 0 /* Direction unknown. */ 89 # endif 90 91 # if STACK_DIRECTION != 0 92 93 # define STACK_DIR STACK_DIRECTION /* Known at compile-time. */ 94 95 # else /* STACK_DIRECTION == 0; need run-time code. */ 96 97 static int stack_dir; /* 1 or -1 once known. */ 98 # define STACK_DIR stack_dir 99 100 static void 101 find_stack_direction (void) 102 { 103 static char *addr = NULL; /* Address of first `dummy', once known. */ 104 auto char dummy; /* To get stack address. */ 105 106 if (addr == NULL) 107 { /* Initial entry. */ 108 addr = ADDRESS_FUNCTION (dummy); 109 110 find_stack_direction (); /* Recurse once. */ 111 } 112 else 113 { 114 /* Second entry. */ 115 if (ADDRESS_FUNCTION (dummy) > addr) 116 stack_dir = 1; /* Stack grew upward. */ 117 else 118 stack_dir = -1; /* Stack grew downward. */ 119 } 120 } 121 122 # endif /* STACK_DIRECTION == 0 */ 123 124 /* An "alloca header" is used to: 125 (a) chain together all alloca'ed blocks; 126 (b) keep track of stack depth. 127 128 It is very important that sizeof(header) agree with malloc 129 alignment chunk size. The following default should work okay. */ 130 131 # ifndef ALIGN_SIZE 132 # define ALIGN_SIZE sizeof(double) 133 # endif 134 135 typedef union hdr 136 { 137 char align[ALIGN_SIZE]; /* To force sizeof(header). */ 138 struct 139 { 140 union hdr *next; /* For chaining headers. */ 141 char *deep; /* For stack depth measure. */ 142 } h; 143 } header; 144 145 static header *last_alloca_header = NULL; /* -> last alloca header. */ 146 147 /* Return a pointer to at least SIZE bytes of storage, 148 which will be automatically reclaimed upon exit from 149 the procedure that called alloca. Originally, this space 150 was supposed to be taken from the current stack frame of the 151 caller, but that method cannot be made to work for some 152 implementations of C, for example under Gould's UTX/32. */ 153 154 void * 155 alloca (size_t size) 156 { 157 auto char probe; /* Probes stack depth: */ 158 register char *depth = ADDRESS_FUNCTION (probe); 159 160 # if STACK_DIRECTION == 0 161 if (STACK_DIR == 0) /* Unknown growth direction. */ 162 find_stack_direction (); 163 # endif 164 165 /* Reclaim garbage, defined as all alloca'd storage that 166 was allocated from deeper in the stack than currently. */ 167 168 { 169 register header *hp; /* Traverses linked list. */ 170 171 # ifdef emacs 172 BLOCK_INPUT; 173 # endif 174 175 for (hp = last_alloca_header; hp != NULL;) 176 if ((STACK_DIR > 0 && hp->h.deep > depth) 177 || (STACK_DIR < 0 && hp->h.deep < depth)) 178 { 179 register header *np = hp->h.next; 180 181 free (hp); /* Collect garbage. */ 182 183 hp = np; /* -> next header. */ 184 } 185 else 186 break; /* Rest are not deeper. */ 187 188 last_alloca_header = hp; /* -> last valid storage. */ 189 190 # ifdef emacs 191 UNBLOCK_INPUT; 192 # endif 193 } 194 195 if (size == 0) 196 return NULL; /* No allocation required. */ 197 198 /* Allocate combined header + user data storage. */ 199 200 { 201 /* Address of header. */ 202 register header *new; 203 204 size_t combined_size = sizeof (header) + size; 205 if (combined_size < sizeof (header)) 206 memory_full (); 207 208 new = malloc (combined_size); 209 210 if (! new) 211 memory_full (); 212 213 new->h.next = last_alloca_header; 214 new->h.deep = depth; 215 216 last_alloca_header = new; 217 218 /* User storage begins just after header. */ 219 220 return (void *) (new + 1); 221 } 222 } 223 224 # if defined (CRAY) && defined (CRAY_STACKSEG_END) 225 226 # ifdef DEBUG_I00AFUNC 227 # include <stdio.h> 228 # endif 229 230 # ifndef CRAY_STACK 231 # define CRAY_STACK 232 # ifndef CRAY2 233 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ 234 struct stack_control_header 235 { 236 long shgrow:32; /* Number of times stack has grown. */ 237 long shaseg:32; /* Size of increments to stack. */ 238 long shhwm:32; /* High water mark of stack. */ 239 long shsize:32; /* Current size of stack (all segments). */ 240 }; 241 242 /* The stack segment linkage control information occurs at 243 the high-address end of a stack segment. (The stack 244 grows from low addresses to high addresses.) The initial 245 part of the stack segment linkage control information is 246 0200 (octal) words. This provides for register storage 247 for the routine which overflows the stack. */ 248 249 struct stack_segment_linkage 250 { 251 long ss[0200]; /* 0200 overflow words. */ 252 long sssize:32; /* Number of words in this segment. */ 253 long ssbase:32; /* Offset to stack base. */ 254 long:32; 255 long sspseg:32; /* Offset to linkage control of previous 256 segment of stack. */ 257 long:32; 258 long sstcpt:32; /* Pointer to task common address block. */ 259 long sscsnm; /* Private control structure number for 260 microtasking. */ 261 long ssusr1; /* Reserved for user. */ 262 long ssusr2; /* Reserved for user. */ 263 long sstpid; /* Process ID for pid based multi-tasking. */ 264 long ssgvup; /* Pointer to multitasking thread giveup. */ 265 long sscray[7]; /* Reserved for Cray Research. */ 266 long ssa0; 267 long ssa1; 268 long ssa2; 269 long ssa3; 270 long ssa4; 271 long ssa5; 272 long ssa6; 273 long ssa7; 274 long sss0; 275 long sss1; 276 long sss2; 277 long sss3; 278 long sss4; 279 long sss5; 280 long sss6; 281 long sss7; 282 }; 283 284 # else /* CRAY2 */ 285 /* The following structure defines the vector of words 286 returned by the STKSTAT library routine. */ 287 struct stk_stat 288 { 289 long now; /* Current total stack size. */ 290 long maxc; /* Amount of contiguous space which would 291 be required to satisfy the maximum 292 stack demand to date. */ 293 long high_water; /* Stack high-water mark. */ 294 long overflows; /* Number of stack overflow ($STKOFEN) calls. */ 295 long hits; /* Number of internal buffer hits. */ 296 long extends; /* Number of block extensions. */ 297 long stko_mallocs; /* Block allocations by $STKOFEN. */ 298 long underflows; /* Number of stack underflow calls ($STKRETN). */ 299 long stko_free; /* Number of deallocations by $STKRETN. */ 300 long stkm_free; /* Number of deallocations by $STKMRET. */ 301 long segments; /* Current number of stack segments. */ 302 long maxs; /* Maximum number of stack segments so far. */ 303 long pad_size; /* Stack pad size. */ 304 long current_address; /* Current stack segment address. */ 305 long current_size; /* Current stack segment size. This 306 number is actually corrupted by STKSTAT to 307 include the fifteen word trailer area. */ 308 long initial_address; /* Address of initial segment. */ 309 long initial_size; /* Size of initial segment. */ 310 }; 311 312 /* The following structure describes the data structure which trails 313 any stack segment. I think that the description in 'asdef' is 314 out of date. I only describe the parts that I am sure about. */ 315 316 struct stk_trailer 317 { 318 long this_address; /* Address of this block. */ 319 long this_size; /* Size of this block (does not include 320 this trailer). */ 321 long unknown2; 322 long unknown3; 323 long link; /* Address of trailer block of previous 324 segment. */ 325 long unknown5; 326 long unknown6; 327 long unknown7; 328 long unknown8; 329 long unknown9; 330 long unknown10; 331 long unknown11; 332 long unknown12; 333 long unknown13; 334 long unknown14; 335 }; 336 337 # endif /* CRAY2 */ 338 # endif /* not CRAY_STACK */ 339 340 # ifdef CRAY2 341 /* Determine a "stack measure" for an arbitrary ADDRESS. 342 I doubt that "lint" will like this much. */ 343 344 static long 345 i00afunc (long *address) 346 { 347 struct stk_stat status; 348 struct stk_trailer *trailer; 349 long *block, size; 350 long result = 0; 351 352 /* We want to iterate through all of the segments. The first 353 step is to get the stack status structure. We could do this 354 more quickly and more directly, perhaps, by referencing the 355 $LM00 common block, but I know that this works. */ 356 357 STKSTAT (&status); 358 359 /* Set up the iteration. */ 360 361 trailer = (struct stk_trailer *) (status.current_address 362 + status.current_size 363 - 15); 364 365 /* There must be at least one stack segment. Therefore it is 366 a fatal error if "trailer" is null. */ 367 368 if (trailer == 0) 369 abort (); 370 371 /* Discard segments that do not contain our argument address. */ 372 373 while (trailer != 0) 374 { 375 block = (long *) trailer->this_address; 376 size = trailer->this_size; 377 if (block == 0 || size == 0) 378 abort (); 379 trailer = (struct stk_trailer *) trailer->link; 380 if ((block <= address) && (address < (block + size))) 381 break; 382 } 383 384 /* Set the result to the offset in this segment and add the sizes 385 of all predecessor segments. */ 386 387 result = address - block; 388 389 if (trailer == 0) 390 { 391 return result; 392 } 393 394 do 395 { 396 if (trailer->this_size <= 0) 397 abort (); 398 result += trailer->this_size; 399 trailer = (struct stk_trailer *) trailer->link; 400 } 401 while (trailer != 0); 402 403 /* We are done. Note that if you present a bogus address (one 404 not in any segment), you will get a different number back, formed 405 from subtracting the address of the first block. This is probably 406 not what you want. */ 407 408 return (result); 409 } 410 411 # else /* not CRAY2 */ 412 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. 413 Determine the number of the cell within the stack, 414 given the address of the cell. The purpose of this 415 routine is to linearize, in some sense, stack addresses 416 for alloca. */ 417 418 static long 419 i00afunc (long address) 420 { 421 long stkl = 0; 422 423 long size, pseg, this_segment, stack; 424 long result = 0; 425 426 struct stack_segment_linkage *ssptr; 427 428 /* Register B67 contains the address of the end of the 429 current stack segment. If you (as a subprogram) store 430 your registers on the stack and find that you are past 431 the contents of B67, you have overflowed the segment. 432 433 B67 also points to the stack segment linkage control 434 area, which is what we are really interested in. */ 435 436 stkl = CRAY_STACKSEG_END (); 437 ssptr = (struct stack_segment_linkage *) stkl; 438 439 /* If one subtracts 'size' from the end of the segment, 440 one has the address of the first word of the segment. 441 442 If this is not the first segment, 'pseg' will be 443 nonzero. */ 444 445 pseg = ssptr->sspseg; 446 size = ssptr->sssize; 447 448 this_segment = stkl - size; 449 450 /* It is possible that calling this routine itself caused 451 a stack overflow. Discard stack segments which do not 452 contain the target address. */ 453 454 while (!(this_segment <= address && address <= stkl)) 455 { 456 # ifdef DEBUG_I00AFUNC 457 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); 458 # endif 459 if (pseg == 0) 460 break; 461 stkl = stkl - pseg; 462 ssptr = (struct stack_segment_linkage *) stkl; 463 size = ssptr->sssize; 464 pseg = ssptr->sspseg; 465 this_segment = stkl - size; 466 } 467 468 result = address - this_segment; 469 470 /* If you subtract pseg from the current end of the stack, 471 you get the address of the previous stack segment's end. 472 This seems a little convoluted to me, but I'll bet you save 473 a cycle somewhere. */ 474 475 while (pseg != 0) 476 { 477 # ifdef DEBUG_I00AFUNC 478 fprintf (stderr, "%011o %011o\n", pseg, size); 479 # endif 480 stkl = stkl - pseg; 481 ssptr = (struct stack_segment_linkage *) stkl; 482 size = ssptr->sssize; 483 pseg = ssptr->sspseg; 484 result += size; 485 } 486 return (result); 487 } 488 489 # endif /* not CRAY2 */ 490 # endif /* CRAY */ 491 492 # endif /* no alloca */ 493 #endif /* not GCC version 2 */ 494