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