wrlib/alloca.c

   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 #ifdef HAVE_CONFIG_H
  25 #include <config.h>
  26 #endif
  27
  28 #ifdef HAVE_STRING_H
  29 #include <string.h>
  30 #endif
  31 #ifdef HAVE_STDLIB_H
  32 #include <stdlib.h>
  33 #endif
  34
  35 #ifdef emacs
  36 #include "blockinput.h"
  37 #endif
  38
  39 /* If compiling with GCC 2, this file's not needed.  */
  40 #if !defined (__GNUC__) || __GNUC__ < 2
  41
  42 /* If someone has defined alloca as a macro,
  43  there must be some other way alloca is supposed to work.  */
  44 #ifndef alloca
  45
  46 #ifdef emacs
  47 #ifdef static
  48 /* actually, only want this if static is defined as ""
  49  -- this is for usg, in which emacs must undefine static
  50  in order to make unexec workable
  51  */
  52 #ifndef STACK_DIRECTION
  53 you lose-- must know STACK_DIRECTION at compile - time
  54 #endif                          /* STACK_DIRECTION undefined */
  55 #endif                          /* static */
  56 #endif                          /* emacs */
  57 /* If your stack is a linked list of frames, you have to
  58    provide an "address metric" ADDRESS_FUNCTION macro.  */
  59 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
  60 long i00afunc();
  61 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
  62 #else
  63 #define ADDRESS_FUNCTION(arg) &(arg)
  64 #endif
  65 #if __STDC__
  66 typedef void *pointer;
  67 #else
  68 typedef char *pointer;
  69 #endif
  70
  71 #ifndef NULL
  72 #define NULL    0
  73 #endif
  74
  75 /* Different portions of Emacs need to call different versions of
  76  malloc.  The Emacs executable needs alloca to call xmalloc, because
  77  ordinary malloc isn't protected from input signals.  On the other
  78  hand, the utilities in lib-src need alloca to call malloc; some of
  79  them are very simple, and don't have an xmalloc routine.
  80
  81  Non-Emacs programs expect this to call use xmalloc.
  82
  83  Callers below should use malloc.  */
  84
  85 #ifndef emacs
  86 #define malloc xmalloc
  87 #endif
  88 extern pointer malloc();
  89
  90 /* Define STACK_DIRECTION if you know the direction of stack
  91  growth for your system; otherwise it will be automatically
  92  deduced at run-time.
  93
  94  STACK_DIRECTION > 0 => grows toward higher addresses
  95  STACK_DIRECTION < 0 => grows toward lower addresses
  96  STACK_DIRECTION = 0 => direction of growth unknown  */
  97
  98 #ifndef STACK_DIRECTION
  99 #define STACK_DIRECTION 0       /* Direction unknown.  */
 100 #endif
 101
 102 #if STACK_DIRECTION != 0
 103
 104 #define STACK_DIR       STACK_DIRECTION /* Known at compile-time.  */
 105
 106 #else                           /* STACK_DIRECTION == 0; need run-time code.  */
 107
 108 static int stack_dir;           /* 1 or -1 once known.  */
 109 #define STACK_DIR       stack_dir
 110
 111 static void find_stack_direction()
 112 {
 113         static char *addr = NULL;       /* Address of first `dummy', once known.  */
 114         auto char dummy;        /* To get stack address.  */
 115
 116         if (addr == NULL) {     /* Initial entry.  */
 117                 addr = ADDRESS_FUNCTION(dummy);
 118
 119                 find_stack_direction(); /* Recurse once.  */
 120         } else {
 121                 /* Second entry.  */
 122                 if (ADDRESS_FUNCTION(dummy) > addr)
 123                         stack_dir = 1;  /* Stack grew upward.  */
 124                 else
 125                         stack_dir = -1; /* Stack grew downward.  */
 126         }
 127 }
 128
 129 #endif                          /* STACK_DIRECTION == 0 */
 130
 131 /* An "alloca header" is used to:
 132  (a) chain together all alloca'ed blocks;
 133  (b) keep track of stack depth.
 134
 135  It is very important that sizeof(header) agree with malloc
 136  alignment chunk size.  The following default should work okay.  */
 137
 138 #ifndef ALIGN_SIZE
 139 #define ALIGN_SIZE      sizeof(double)
 140 #endif
 141
 142 typedef union hdr {
 143         char align[ALIGN_SIZE]; /* To force sizeof(header).  */
 144         struct {
 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 pointer alloca(size)
 160 unsigned size;
 161 {
 162         auto char probe;        /* Probes stack depth: */
 163         register char *depth = ADDRESS_FUNCTION(probe);
 164
 165 #if STACK_DIRECTION == 0
 166         if (STACK_DIR == 0)     /* Unknown growth direction.  */
 167                 find_stack_direction();
 168 #endif
 169
 170         /* Reclaim garbage, defined as all alloca'd storage that
 171            was allocated from deeper in the stack than currently. */
 172
 173         {
 174                 register header *hp;    /* Traverses linked list.  */
 175
 176 #ifdef emacs
 177                 BLOCK_INPUT;
 178 #endif
 179
 180                 for (hp = last_alloca_header; hp != NULL;)
 181                         if ((STACK_DIR > 0 && hp->h.deep > depth)
 182                             || (STACK_DIR < 0 && hp->h.deep < depth)) {
 183                                 register header *np = hp->h.next;
 184
 185                                 free((pointer) hp);     /* Collect garbage.  */
 186
 187                                 hp = np;        /* -> next header.  */
 188                         } else
 189                                 break;  /* Rest are not deeper.  */
 190
 191                 last_alloca_header = hp;        /* -> last valid storage.  */
 192
 193 #ifdef emacs
 194                 UNBLOCK_INPUT;
 195 #endif
 196         }
 197
 198         if (size == 0)
 199                 return NULL;    /* No allocation required.  */
 200
 201         /* Allocate combined header + user data storage.  */
 202
 203         {
 204                 register pointer new = malloc(sizeof(header) + size);
 205                 /* Address of header.  */
 206
 207                 if (new == 0)
 208                         abort();
 209
 210                 ((header *) new)->h.next = last_alloca_header;
 211                 ((header *) new)->h.deep = depth;
 212
 213                 last_alloca_header = (header *) new;
 214
 215                 /* User storage begins just after header.  */
 216
 217                 return (pointer) ((char *)new + sizeof(header));
 218         }
 219 }
 220
 221 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
 222
 223 #ifdef DEBUG_I00AFUNC
 224 #include <stdio.h>
 225 #endif
 226
 227 #ifndef CRAY_STACK
 228 #define CRAY_STACK
 229 #ifndef CRAY2
 230 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
 231 struct stack_control_header {
 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
 245 struct stack_segment_linkage {
 246         long ss[0200];          /* 0200 overflow words.  */
 247         long sssize:32;         /* Number of words in this segment.  */
 248         long ssbase:32;         /* Offset to stack base.  */
 249         long:32;
 250         long sspseg:32;         /* Offset to linkage control of previous
 251                                    segment of stack.  */
 252         long:32;
 253         long sstcpt:32;         /* Pointer to task common address block.  */
 254         long sscsnm;            /* Private control structure number for
 255                                    microtasking.  */
 256         long ssusr1;            /* Reserved for user.  */
 257         long ssusr2;            /* Reserved for user.  */
 258         long sstpid;            /* Process ID for pid based multi-tasking.  */
 259         long ssgvup;            /* Pointer to multitasking thread giveup.  */
 260         long sscray[7];         /* Reserved for Cray Research.  */
 261         long ssa0;
 262         long ssa1;
 263         long ssa2;
 264         long ssa3;
 265         long ssa4;
 266         long ssa5;
 267         long ssa6;
 268         long ssa7;
 269         long sss0;
 270         long sss1;
 271         long sss2;
 272         long sss3;
 273         long sss4;
 274         long sss5;
 275         long sss6;
 276         long sss7;
 277 };
 278
 279 #else                           /* CRAY2 */
 280 /* The following structure defines the vector of words
 281  returned by the STKSTAT library routine.  */
 282 struct stk_stat {
 283         long now;               /* Current total stack size.  */
 284         long maxc;              /* Amount of contiguous space which would
 285                                    be required to satisfy the maximum
 286                                    stack demand to date.  */
 287         long high_water;        /* Stack high-water mark.  */
 288         long overflows;         /* Number of stack overflow ($STKOFEN) calls.  */
 289         long hits;              /* Number of internal buffer hits.  */
 290         long extends;           /* Number of block extensions.  */
 291         long stko_mallocs;      /* Block allocations by $STKOFEN.  */
 292         long underflows;        /* Number of stack underflow calls ($STKRETN).  */
 293         long stko_free;         /* Number of deallocations by $STKRETN.  */
 294         long stkm_free;         /* Number of deallocations by $STKMRET.  */
 295         long segments;          /* Current number of stack segments.  */
 296         long maxs;              /* Maximum number of stack segments so far.  */
 297         long pad_size;          /* Stack pad size.  */
 298         long current_address;   /* Current stack segment address.  */
 299         long current_size;      /* Current stack segment size.  This
 300                                    number is actually corrupted by STKSTAT to
 301                                    include the fifteen word trailer area.  */
 302         long initial_address;   /* Address of initial segment.  */
 303         long initial_size;      /* Size of initial segment.  */
 304 };
 305
 306 /* The following structure describes the data structure which trails
 307  any stack segment.  I think that the description in 'asdef' is
 308  out of date.  I only describe the parts that I am sure about.  */
 309
 310 struct stk_trailer {
 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 i00afunc(long *address)
 338 {
 339         struct stk_stat status;
 340         struct stk_trailer *trailer;
 341         long *block, size;
 342         long result = 0;
 343
 344         /* We want to iterate through all of the segments.  The first
 345            step is to get the stack status structure.  We could do this
 346            more quickly and more directly, perhaps, by referencing the
 347            $LM00 common block, but I know that this works.  */
 348
 349         STKSTAT(&status);
 350
 351         /* Set up the iteration.  */
 352
 353         trailer = (struct stk_trailer *)(status.current_address + status.current_size - 15);
 354
 355         /* There must be at least one stack segment.  Therefore it is
 356            a fatal error if "trailer" is null.  */
 357
 358         if (trailer == 0)
 359                 abort();
 360
 361         /* Discard segments that do not contain our argument address.  */
 362
 363         while (trailer != 0) {
 364                 block = (long *)trailer->this_address;
 365                 size = trailer->this_size;
 366                 if (block == 0 || size == 0)
 367                         abort();
 368                 trailer = (struct stk_trailer *)trailer->link;
 369                 if ((block <= address) && (address < (block + size)))
 370                         break;
 371         }
 372
 373         /* Set the result to the offset in this segment and add the sizes
 374            of all predecessor segments.  */
 375
 376         result = address - block;
 377
 378         if (trailer == 0) {
 379                 return result;
 380         }
 381
 382         do {
 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 i00afunc(long address)
 406 {
 407         long stkl = 0;
 408
 409         long size, pseg, this_segment, stack;
 410         long result = 0;
 411
 412         struct stack_segment_linkage *ssptr;
 413
 414         /* Register B67 contains the address of the end of the
 415            current stack segment.  If you (as a subprogram) store
 416            your registers on the stack and find that you are past
 417            the contents of B67, you have overflowed the segment.
 418
 419            B67 also points to the stack segment linkage control
 420            area, which is what we are really interested in.  */
 421
 422         stkl = CRAY_STACKSEG_END();
 423         ssptr = (struct stack_segment_linkage *)stkl;
 424
 425         /* If one subtracts 'size' from the end of the segment,
 426            one has the address of the first word of the segment.
 427
 428            If this is not the first segment, 'pseg' will be
 429            nonzero.  */
 430
 431         pseg = ssptr->sspseg;
 432         size = ssptr->sssize;
 433
 434         this_segment = stkl - size;
 435
 436         /* It is possible that calling this routine itself caused
 437            a stack overflow.  Discard stack segments which do not
 438            contain the target address.  */
 439
 440         while (!(this_segment <= address && address <= stkl)) {
 441 #ifdef DEBUG_I00AFUNC
 442                 fprintf(stderr, "%011o %011o %011o\n", this_segment, address, stkl);
 443 #endif
 444                 if (pseg == 0)
 445                         break;
 446                 stkl = stkl - pseg;
 447                 ssptr = (struct stack_segment_linkage *)stkl;
 448                 size = ssptr->sssize;
 449                 pseg = ssptr->sspseg;
 450                 this_segment = stkl - size;
 451         }
 452
 453         result = address - this_segment;
 454
 455         /* If you subtract pseg from the current end of the stack,
 456            you get the address of the previous stack segment's end.
 457            This seems a little convoluted to me, but I'll bet you save
 458            a cycle somewhere.  */
 459
 460         while (pseg != 0) {
 461 #ifdef DEBUG_I00AFUNC
 462                 fprintf(stderr, "%011o %011o\n", pseg, size);
 463 #endif
 464                 stkl = stkl - pseg;
 465                 ssptr = (struct stack_segment_linkage *)stkl;
 466                 size = ssptr->sssize;
 467                 pseg = ssptr->sspseg;
 468                 result += size;
 469         }
 470         return (result);
 471 }
 472
 473 #endif                          /* not CRAY2 */
 474 #endif                          /* CRAY */
 475
 476 #endif                          /* no alloca */
 477 #endif                          /* not GCC version 2 */