1 /* $NetBSD: alloca.c,v 1.1.1.1 2016/01/10 21:36:18 christos Exp $ */ 2 3 /* alloca.c -- allocate automatically reclaimed memory 4 (Mostly) portable public-domain implementation -- D A Gwyn 5 6 This implementation of the PWB library alloca function, 7 which is used to allocate space off the run-time stack so 8 that it is automatically reclaimed upon procedure exit, 9 was inspired by discussions with J. Q. Johnson of Cornell. 10 J.Otto Tennant <jot@cray.com> contributed the Cray support. 11 12 There are some preprocessor constants that can 13 be defined when compiling for your specific system, for 14 improved efficiency; however, the defaults should be okay. 15 16 The general concept of this implementation is to keep 17 track of all alloca-allocated blocks, and reclaim any 18 that are found to be deeper in the stack than the current 19 invocation. This heuristic does not reclaim storage as 20 soon as it becomes invalid, but it will do so eventually. 21 22 As a special case, alloca(0) reclaims storage without 23 allocating any. It is a good idea to use alloca(0) in 24 your main control loop, etc. to force garbage collection. */ 25 26 #ifdef HAVE_CONFIG_H 27 # include <config.h> 28 #endif 29 30 #if HAVE_STRING_H 31 # include <string.h> 32 #endif 33 #if HAVE_STDLIB_H 34 # include <stdlib.h> 35 #endif 36 37 #ifdef emacs 38 # include "blockinput.h" 39 #endif 40 41 /* If compiling with GCC 2, this file's not needed. */ 42 #if !defined (__GNUC__) || __GNUC__ < 2 43 44 /* If someone has defined alloca as a macro, 45 there must be some other way alloca is supposed to work. */ 46 # ifndef alloca 47 48 # ifdef emacs 49 # ifdef static 50 /* actually, only want this if static is defined as "" 51 -- this is for usg, in which emacs must undefine static 52 in order to make unexec workable 53 */ 54 # ifndef STACK_DIRECTION 55 you 56 lose 57 -- must know STACK_DIRECTION at compile-time 58 # endif /* STACK_DIRECTION undefined */ 59 # endif /* static */ 60 # endif /* emacs */ 61 62 /* If your stack is a linked list of frames, you have to 63 provide an "address metric" ADDRESS_FUNCTION macro. */ 64 65 # if defined (CRAY) && defined (CRAY_STACKSEG_END) 66 long i00afunc (); 67 # define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) 68 # else 69 # define ADDRESS_FUNCTION(arg) &(arg) 70 # endif 71 72 # if __STDC__ 73 typedef void *pointer; 74 # else 75 typedef char *pointer; 76 # endif 77 78 # ifndef NULL 79 # define NULL 0 80 # endif 81 82 /* Different portions of Emacs need to call different versions of 83 malloc. The Emacs executable needs alloca to call xmalloc, because 84 ordinary malloc isn't protected from input signals. On the other 85 hand, the utilities in lib-src need alloca to call malloc; some of 86 them are very simple, and don't have an xmalloc routine. 87 88 Non-Emacs programs expect this to call xmalloc. 89 90 Callers below should use malloc. */ 91 92 # ifndef emacs 93 # define malloc xmalloc 94 # endif 95 extern pointer malloc (); 96 97 /* Define STACK_DIRECTION if you know the direction of stack 98 growth for your system; otherwise it will be automatically 99 deduced at run-time. 100 101 STACK_DIRECTION > 0 => grows toward higher addresses 102 STACK_DIRECTION < 0 => grows toward lower addresses 103 STACK_DIRECTION = 0 => direction of growth unknown */ 104 105 # ifndef STACK_DIRECTION 106 # define STACK_DIRECTION 0 /* Direction unknown. */ 107 # endif 108 109 # if STACK_DIRECTION != 0 110 111 # define STACK_DIR STACK_DIRECTION /* Known at compile-time. */ 112 113 # else /* STACK_DIRECTION == 0; need run-time code. */ 114 115 static int stack_dir; /* 1 or -1 once known. */ 116 # define STACK_DIR stack_dir 117 118 static void 119 find_stack_direction () 120 { 121 static char *addr = NULL; /* Address of first `dummy', once known. */ 122 auto char dummy; /* To get stack address. */ 123 124 if (addr == NULL) 125 { /* Initial entry. */ 126 addr = ADDRESS_FUNCTION (dummy); 127 128 find_stack_direction (); /* Recurse once. */ 129 } 130 else 131 { 132 /* Second entry. */ 133 if (ADDRESS_FUNCTION (dummy) > addr) 134 stack_dir = 1; /* Stack grew upward. */ 135 else 136 stack_dir = -1; /* Stack grew downward. */ 137 } 138 } 139 140 # endif /* STACK_DIRECTION == 0 */ 141 142 /* An "alloca header" is used to: 143 (a) chain together all alloca'ed blocks; 144 (b) keep track of stack depth. 145 146 It is very important that sizeof(header) agree with malloc 147 alignment chunk size. The following default should work okay. */ 148 149 # ifndef ALIGN_SIZE 150 # define ALIGN_SIZE sizeof(double) 151 # endif 152 153 typedef union hdr 154 { 155 char align[ALIGN_SIZE]; /* To force sizeof(header). */ 156 struct 157 { 158 union hdr *next; /* For chaining headers. */ 159 char *deep; /* For stack depth measure. */ 160 } h; 161 } header; 162 163 static header *last_alloca_header = NULL; /* -> last alloca header. */ 164 165 /* Return a pointer to at least SIZE bytes of storage, 166 which will be automatically reclaimed upon exit from 167 the procedure that called alloca. Originally, this space 168 was supposed to be taken from the current stack frame of the 169 caller, but that method cannot be made to work for some 170 implementations of C, for example under Gould's UTX/32. */ 171 172 pointer 173 alloca (unsigned size) 174 { 175 auto char probe; /* Probes stack depth: */ 176 register char *depth = ADDRESS_FUNCTION (probe); 177 178 # if STACK_DIRECTION == 0 179 if (STACK_DIR == 0) /* Unknown growth direction. */ 180 find_stack_direction (); 181 # endif 182 183 /* Reclaim garbage, defined as all alloca'd storage that 184 was allocated from deeper in the stack than currently. */ 185 186 { 187 register header *hp; /* Traverses linked list. */ 188 189 # ifdef emacs 190 BLOCK_INPUT; 191 # endif 192 193 for (hp = last_alloca_header; hp != NULL;) 194 if ((STACK_DIR > 0 && hp->h.deep > depth) 195 || (STACK_DIR < 0 && hp->h.deep < depth)) 196 { 197 register header *np = hp->h.next; 198 199 free ((pointer) hp); /* Collect garbage. */ 200 201 hp = np; /* -> next header. */ 202 } 203 else 204 break; /* Rest are not deeper. */ 205 206 last_alloca_header = hp; /* -> last valid storage. */ 207 208 # ifdef emacs 209 UNBLOCK_INPUT; 210 # endif 211 } 212 213 if (size == 0) 214 return NULL; /* No allocation required. */ 215 216 /* Allocate combined header + user data storage. */ 217 218 { 219 register pointer new = malloc (sizeof (header) + size); 220 /* Address of header. */ 221 222 if (new == 0) 223 abort(); 224 225 ((header *) new)->h.next = last_alloca_header; 226 ((header *) new)->h.deep = depth; 227 228 last_alloca_header = (header *) new; 229 230 /* User storage begins just after header. */ 231 232 return (pointer) ((char *) new + sizeof (header)); 233 } 234 } 235 236 # if defined (CRAY) && defined (CRAY_STACKSEG_END) 237 238 # ifdef DEBUG_I00AFUNC 239 # include <stdio.h> 240 # endif 241 242 # ifndef CRAY_STACK 243 # define CRAY_STACK 244 # ifndef CRAY2 245 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ 246 struct stack_control_header 247 { 248 long shgrow:32; /* Number of times stack has grown. */ 249 long shaseg:32; /* Size of increments to stack. */ 250 long shhwm:32; /* High water mark of stack. */ 251 long shsize:32; /* Current size of stack (all segments). */ 252 }; 253 254 /* The stack segment linkage control information occurs at 255 the high-address end of a stack segment. (The stack 256 grows from low addresses to high addresses.) The initial 257 part of the stack segment linkage control information is 258 0200 (octal) words. This provides for register storage 259 for the routine which overflows the stack. */ 260 261 struct stack_segment_linkage 262 { 263 long ss[0200]; /* 0200 overflow words. */ 264 long sssize:32; /* Number of words in this segment. */ 265 long ssbase:32; /* Offset to stack base. */ 266 long:32; 267 long sspseg:32; /* Offset to linkage control of previous 268 segment of stack. */ 269 long:32; 270 long sstcpt:32; /* Pointer to task common address block. */ 271 long sscsnm; /* Private control structure number for 272 microtasking. */ 273 long ssusr1; /* Reserved for user. */ 274 long ssusr2; /* Reserved for user. */ 275 long sstpid; /* Process ID for pid based multi-tasking. */ 276 long ssgvup; /* Pointer to multitasking thread giveup. */ 277 long sscray[7]; /* Reserved for Cray Research. */ 278 long ssa0; 279 long ssa1; 280 long ssa2; 281 long ssa3; 282 long ssa4; 283 long ssa5; 284 long ssa6; 285 long ssa7; 286 long sss0; 287 long sss1; 288 long sss2; 289 long sss3; 290 long sss4; 291 long sss5; 292 long sss6; 293 long sss7; 294 }; 295 296 # else /* CRAY2 */ 297 /* The following structure defines the vector of words 298 returned by the STKSTAT library routine. */ 299 struct stk_stat 300 { 301 long now; /* Current total stack size. */ 302 long maxc; /* Amount of contiguous space which would 303 be required to satisfy the maximum 304 stack demand to date. */ 305 long high_water; /* Stack high-water mark. */ 306 long overflows; /* Number of stack overflow ($STKOFEN) calls. */ 307 long hits; /* Number of internal buffer hits. */ 308 long extends; /* Number of block extensions. */ 309 long stko_mallocs; /* Block allocations by $STKOFEN. */ 310 long underflows; /* Number of stack underflow calls ($STKRETN). */ 311 long stko_free; /* Number of deallocations by $STKRETN. */ 312 long stkm_free; /* Number of deallocations by $STKMRET. */ 313 long segments; /* Current number of stack segments. */ 314 long maxs; /* Maximum number of stack segments so far. */ 315 long pad_size; /* Stack pad size. */ 316 long current_address; /* Current stack segment address. */ 317 long current_size; /* Current stack segment size. This 318 number is actually corrupted by STKSTAT to 319 include the fifteen word trailer area. */ 320 long initial_address; /* Address of initial segment. */ 321 long initial_size; /* Size of initial segment. */ 322 }; 323 324 /* The following structure describes the data structure which trails 325 any stack segment. I think that the description in 'asdef' is 326 out of date. I only describe the parts that I am sure about. */ 327 328 struct stk_trailer 329 { 330 long this_address; /* Address of this block. */ 331 long this_size; /* Size of this block (does not include 332 this trailer). */ 333 long unknown2; 334 long unknown3; 335 long link; /* Address of trailer block of previous 336 segment. */ 337 long unknown5; 338 long unknown6; 339 long unknown7; 340 long unknown8; 341 long unknown9; 342 long unknown10; 343 long unknown11; 344 long unknown12; 345 long unknown13; 346 long unknown14; 347 }; 348 349 # endif /* CRAY2 */ 350 # endif /* not CRAY_STACK */ 351 352 # ifdef CRAY2 353 /* Determine a "stack measure" for an arbitrary ADDRESS. 354 I doubt that "lint" will like this much. */ 355 356 static long 357 i00afunc (long *address) 358 { 359 struct stk_stat status; 360 struct stk_trailer *trailer; 361 long *block, size; 362 long result = 0; 363 364 /* We want to iterate through all of the segments. The first 365 step is to get the stack status structure. We could do this 366 more quickly and more directly, perhaps, by referencing the 367 $LM00 common block, but I know that this works. */ 368 369 STKSTAT (&status); 370 371 /* Set up the iteration. */ 372 373 trailer = (struct stk_trailer *) (status.current_address 374 + status.current_size 375 - 15); 376 377 /* There must be at least one stack segment. Therefore it is 378 a fatal error if "trailer" is null. */ 379 380 if (trailer == 0) 381 abort (); 382 383 /* Discard segments that do not contain our argument address. */ 384 385 while (trailer != 0) 386 { 387 block = (long *) trailer->this_address; 388 size = trailer->this_size; 389 if (block == 0 || size == 0) 390 abort (); 391 trailer = (struct stk_trailer *) trailer->link; 392 if ((block <= address) && (address < (block + size))) 393 break; 394 } 395 396 /* Set the result to the offset in this segment and add the sizes 397 of all predecessor segments. */ 398 399 result = address - block; 400 401 if (trailer == 0) 402 { 403 return result; 404 } 405 406 do 407 { 408 if (trailer->this_size <= 0) 409 abort (); 410 result += trailer->this_size; 411 trailer = (struct stk_trailer *) trailer->link; 412 } 413 while (trailer != 0); 414 415 /* We are done. Note that if you present a bogus address (one 416 not in any segment), you will get a different number back, formed 417 from subtracting the address of the first block. This is probably 418 not what you want. */ 419 420 return (result); 421 } 422 423 # else /* not CRAY2 */ 424 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. 425 Determine the number of the cell within the stack, 426 given the address of the cell. The purpose of this 427 routine is to linearize, in some sense, stack addresses 428 for alloca. */ 429 430 static long 431 i00afunc (long address) 432 { 433 long stkl = 0; 434 435 long size, pseg, this_segment, stack; 436 long result = 0; 437 438 struct stack_segment_linkage *ssptr; 439 440 /* Register B67 contains the address of the end of the 441 current stack segment. If you (as a subprogram) store 442 your registers on the stack and find that you are past 443 the contents of B67, you have overflowed the segment. 444 445 B67 also points to the stack segment linkage control 446 area, which is what we are really interested in. */ 447 448 stkl = CRAY_STACKSEG_END (); 449 ssptr = (struct stack_segment_linkage *) stkl; 450 451 /* If one subtracts 'size' from the end of the segment, 452 one has the address of the first word of the segment. 453 454 If this is not the first segment, 'pseg' will be 455 nonzero. */ 456 457 pseg = ssptr->sspseg; 458 size = ssptr->sssize; 459 460 this_segment = stkl - size; 461 462 /* It is possible that calling this routine itself caused 463 a stack overflow. Discard stack segments which do not 464 contain the target address. */ 465 466 while (!(this_segment <= address && address <= stkl)) 467 { 468 # ifdef DEBUG_I00AFUNC 469 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); 470 # endif 471 if (pseg == 0) 472 break; 473 stkl = stkl - pseg; 474 ssptr = (struct stack_segment_linkage *) stkl; 475 size = ssptr->sssize; 476 pseg = ssptr->sspseg; 477 this_segment = stkl - size; 478 } 479 480 result = address - this_segment; 481 482 /* If you subtract pseg from the current end of the stack, 483 you get the address of the previous stack segment's end. 484 This seems a little convoluted to me, but I'll bet you save 485 a cycle somewhere. */ 486 487 while (pseg != 0) 488 { 489 # ifdef DEBUG_I00AFUNC 490 fprintf (stderr, "%011o %011o\n", pseg, size); 491 # endif 492 stkl = stkl - pseg; 493 ssptr = (struct stack_segment_linkage *) stkl; 494 size = ssptr->sssize; 495 pseg = ssptr->sspseg; 496 result += size; 497 } 498 return (result); 499 } 500 501 # endif /* not CRAY2 */ 502 # endif /* CRAY */ 503 504 # endif /* no alloca */ 505 #endif /* not GCC version 2 */ 506