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