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