src/alloca.c

   1 /* alloca.c -- allocate automatically reclaimed memory
   2    (Mostly) portable public-domain implementation -- D A Gwyn
   3
   4    NOTE: The canonical source of this file is maintained with gnulib.
   5    Bugs can be reported to bug-gnulib@gnu.org.
   6
   7    This implementation of the PWB library alloca function,
   8    which is used to allocate space off the run-time stack so
   9    that it is automatically reclaimed upon procedure exit,
  10    was inspired by discussions with J. Q. Johnson of Cornell.
  11    J.Otto Tennant <jot@cray.com> contributed the Cray support.
  12
  13    There are some preprocessor constants that can
  14    be defined when compiling for your specific system, for
  15    improved efficiency; however, the defaults should be okay.
  16
  17    The general concept of this implementation is to keep
  18    track of all alloca-allocated blocks, and reclaim any
  19    that are found to be deeper in the stack than the current
  20    invocation.  This heuristic does not reclaim storage as
  21    soon as it becomes invalid, but it will do so eventually.
  22
  23    As a special case, alloca(0) reclaims storage without
  24    allocating any.  It is a good idea to use alloca(0) in
  25    your main control loop, etc. to force garbage collection.  */
  26
  27 #ifdef HAVE_CONFIG_H
  28 # include <config.h>
  29 #endif
  30
  31 #ifdef HAVE_STRING_H
  32 # include <string.h>
  33 #endif
  34 #ifdef HAVE_STDLIB_H
  35 # include <stdlib.h>
  36 #endif
  37
  38 #ifdef DO_BLOCK_INPUT
  39 # include "blockinput.h"
  40 #endif
  41
  42 /* If compiling with GCC 2, this file's not needed.  */
  43 #if !defined (__GNUC__) || __GNUC__ < 2
  44
  45 /* If someone has defined alloca as a macro,
  46    there must be some other way alloca is supposed to work.  */
  47 # ifndef alloca
  48
  49 #  ifdef emacs
  50 #   ifdef static
  51 /* actually, only want this if static is defined as ""
  52    -- this is for usg, in which emacs must undefine static
  53    in order to make unexec workable
  54    */
  55 #    ifndef STACK_DIRECTION
  56 you
  57 lose
  58 -- must know STACK_DIRECTION at compile-time
  59 /* Using #error here is not wise since this file should work for
  60    old and obscure compilers.
  61
  62    As far as I know, using it is OK if it's indented -- at least for
  63    pcc-based processors.  -- fx */
  64 #    endif /* STACK_DIRECTION undefined */
  65 #   endif /* static */
  66 #  endif /* emacs */
  67
  68 /* If your stack is a linked list of frames, you have to
  69    provide an "address metric" ADDRESS_FUNCTION macro.  */
  70
  71 #  if defined (CRAY) && defined (CRAY_STACKSEG_END)
  72 long i00afunc ();
  73 #   define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
  74 #  else
  75 #   define ADDRESS_FUNCTION(arg) &(arg)
  76 #  endif
  77
  78 #  ifndef POINTER_TYPE
  79 #   ifdef __STDC__
  80 #    define POINTER_TYPE void
  81 #   else
  82 #    define POINTER_TYPE char
  83 #   endif
  84 #  endif
  85 typedef POINTER_TYPE *pointer;
  86
  87 #  ifndef NULL
  88 #   define NULL 0
  89 #  endif
  90
  91 /* The Emacs executable needs alloca to call xmalloc, because ordinary
  92    malloc isn't protected from input signals.  xmalloc also checks for
  93    out-of-memory errors, so we should use it generally.
  94
  95    Callers below should use malloc.  */
  96
  97 #  undef malloc
  98 #  define malloc xmalloc
  99 #  undef free
 100 #  define free xfree
 101
 102 void *xmalloc _P ((size_t));
 103 void xfree _P ((void *))
 104
 105 /* Define STACK_DIRECTION if you know the direction of stack
 106    growth for your system; otherwise it will be automatically
 107    deduced at run-time.
 108
 109    STACK_DIRECTION > 0 => grows toward higher addresses
 110    STACK_DIRECTION < 0 => grows toward lower addresses
 111    STACK_DIRECTION = 0 => direction of growth unknown  */
 112
 113 #  ifndef STACK_DIRECTION
 114 #   define STACK_DIRECTION      0       /* Direction unknown.  */
 115 #  endif
 116
 117 #  if STACK_DIRECTION != 0
 118
 119 #   define STACK_DIR    STACK_DIRECTION /* Known at compile-time.  */
 120
 121 #  else /* STACK_DIRECTION == 0; need run-time code.  */
 122
 123 static int stack_dir;           /* 1 or -1 once known.  */
 124 #   define STACK_DIR    stack_dir
 125
 126 static void
 127 find_stack_direction ()
 128 {
 129   static char *addr = NULL;     /* Address of first `dummy', once known.  */
 130   auto char dummy;              /* To get stack address.  */
 131
 132   if (addr == NULL)
 133     {                           /* Initial entry.  */
 134       addr = ADDRESS_FUNCTION (dummy);
 135
 136       find_stack_direction ();  /* Recurse once.  */
 137     }
 138   else
 139     {
 140       /* Second entry.  */
 141       if (ADDRESS_FUNCTION (dummy) > addr)
 142         stack_dir = 1;          /* Stack grew upward.  */
 143       else
 144         stack_dir = -1;         /* Stack grew downward.  */
 145     }
 146 }
 147
 148 #  endif /* STACK_DIRECTION == 0 */
 149
 150 /* An "alloca header" is used to:
 151    (a) chain together all alloca'ed blocks;
 152    (b) keep track of stack depth.
 153
 154    It is very important that sizeof(header) agree with malloc
 155    alignment chunk size.  The following default should work okay.  */
 156
 157 #  ifndef       ALIGN_SIZE
 158 #   define ALIGN_SIZE   sizeof(double)
 159 #  endif
 160
 161 typedef union hdr
 162 {
 163   char align[ALIGN_SIZE];       /* To force sizeof(header).  */
 164   struct
 165     {
 166       union hdr *next;          /* For chaining headers.  */
 167       char *deep;               /* For stack depth measure.  */
 168     } h;
 169 } header;
 170
 171 static header *last_alloca_header = NULL;       /* -> last alloca header.  */
 172
 173 /* Return a pointer to at least SIZE bytes of storage,
 174    which will be automatically reclaimed upon exit from
 175    the procedure that called alloca.  Originally, this space
 176    was supposed to be taken from the current stack frame of the
 177    caller, but that method cannot be made to work for some
 178    implementations of C, for example under Gould's UTX/32.  */
 179
 180 pointer
 181 alloca (size)
 182      size_t size;
 183 {
 184   auto char probe;              /* Probes stack depth: */
 185   register char *depth = ADDRESS_FUNCTION (probe);
 186
 187 #  if STACK_DIRECTION == 0
 188   if (STACK_DIR == 0)           /* Unknown growth direction.  */
 189     find_stack_direction ();
 190 #  endif
 191
 192   /* Reclaim garbage, defined as all alloca'd storage that
 193      was allocated from deeper in the stack than currently.  */
 194
 195   {
 196     register header *hp;        /* Traverses linked list.  */
 197
 198 #  ifdef DO_BLOCK_INPUT
 199     BLOCK_INPUT;
 200 #  endif
 201
 202     for (hp = last_alloca_header; hp != NULL;)
 203       if ((STACK_DIR > 0 && hp->h.deep > depth)
 204           || (STACK_DIR < 0 && hp->h.deep < depth))
 205         {
 206           register header *np = hp->h.next;
 207
 208           free ((pointer) hp);  /* Collect garbage.  */
 209
 210           hp = np;              /* -> next header.  */
 211         }
 212       else
 213         break;                  /* Rest are not deeper.  */
 214
 215     last_alloca_header = hp;    /* -> last valid storage.  */
 216
 217 #  ifdef DO_BLOCK_INPUT
 218     UNBLOCK_INPUT;
 219 #  endif
 220   }
 221
 222   if (size == 0)
 223     return NULL;                /* No allocation required.  */
 224
 225   /* Allocate combined header + user data storage.  */
 226
 227   {
 228     /* Address of header.  */
 229     register pointer new = malloc (sizeof (header) + size);
 230
 231     if (new == 0)
 232       abort();
 233
 234     ((header *) new)->h.next = last_alloca_header;
 235     ((header *) new)->h.deep = depth;
 236
 237     last_alloca_header = (header *) new;
 238
 239     /* User storage begins just after header.  */
 240
 241     return (pointer) ((char *) new + sizeof (header));
 242   }
 243 }
 244
 245 #  if defined (CRAY) && defined (CRAY_STACKSEG_END)
 246
 247 #   ifdef DEBUG_I00AFUNC
 248 #    include <stdio.h>
 249 #   endif
 250
 251 #   ifndef CRAY_STACK
 252 #    define CRAY_STACK
 253 #    ifndef CRAY2
 254 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
 255 struct stack_control_header
 256   {
 257     long shgrow:32;             /* Number of times stack has grown.  */
 258     long shaseg:32;             /* Size of increments to stack.  */
 259     long shhwm:32;              /* High water mark of stack.  */
 260     long shsize:32;             /* Current size of stack (all segments).  */
 261   };
 262
 263 /* The stack segment linkage control information occurs at
 264    the high-address end of a stack segment.  (The stack
 265    grows from low addresses to high addresses.)  The initial
 266    part of the stack segment linkage control information is
 267    0200 (octal) words.  This provides for register storage
 268    for the routine which overflows the stack.  */
 269
 270 struct stack_segment_linkage
 271   {
 272     long ss[0200];              /* 0200 overflow words.  */
 273     long sssize:32;             /* Number of words in this segment.  */
 274     long ssbase:32;             /* Offset to stack base.  */
 275     long:32;
 276     long sspseg:32;             /* Offset to linkage control of previous
 277                                    segment of stack.  */
 278     long:32;
 279     long sstcpt:32;             /* Pointer to task common address block.  */
 280     long sscsnm;                /* Private control structure number for
 281                                    microtasking.  */
 282     long ssusr1;                /* Reserved for user.  */
 283     long ssusr2;                /* Reserved for user.  */
 284     long sstpid;                /* Process ID for pid based multi-tasking.  */
 285     long ssgvup;                /* Pointer to multitasking thread giveup.  */
 286     long sscray[7];             /* Reserved for Cray Research.  */
 287     long ssa0;
 288     long ssa1;
 289     long ssa2;
 290     long ssa3;
 291     long ssa4;
 292     long ssa5;
 293     long ssa6;
 294     long ssa7;
 295     long sss0;
 296     long sss1;
 297     long sss2;
 298     long sss3;
 299     long sss4;
 300     long sss5;
 301     long sss6;
 302     long sss7;
 303   };
 304
 305 #    else /* CRAY2 */
 306 /* The following structure defines the vector of words
 307    returned by the STKSTAT library routine.  */
 308 struct stk_stat
 309   {
 310     long now;                   /* Current total stack size.  */
 311     long maxc;                  /* Amount of contiguous space which would
 312                                    be required to satisfy the maximum
 313                                    stack demand to date.  */
 314     long high_water;            /* Stack high-water mark.  */
 315     long overflows;             /* Number of stack overflow ($STKOFEN) calls.  */
 316     long hits;                  /* Number of internal buffer hits.  */
 317     long extends;               /* Number of block extensions.  */
 318     long stko_mallocs;          /* Block allocations by $STKOFEN.  */
 319     long underflows;            /* Number of stack underflow calls ($STKRETN).  */
 320     long stko_free;             /* Number of deallocations by $STKRETN.  */
 321     long stkm_free;             /* Number of deallocations by $STKMRET.  */
 322     long segments;              /* Current number of stack segments.  */
 323     long maxs;                  /* Maximum number of stack segments so far.  */
 324     long pad_size;              /* Stack pad size.  */
 325     long current_address;       /* Current stack segment address.  */
 326     long current_size;          /* Current stack segment size.  This
 327                                    number is actually corrupted by STKSTAT to
 328                                    include the fifteen word trailer area.  */
 329     long initial_address;       /* Address of initial segment.  */
 330     long initial_size;          /* Size of initial segment.  */
 331   };
 332
 333 /* The following structure describes the data structure which trails
 334    any stack segment.  I think that the description in 'asdef' is
 335    out of date.  I only describe the parts that I am sure about.  */
 336
 337 struct stk_trailer
 338   {
 339     long this_address;          /* Address of this block.  */
 340     long this_size;             /* Size of this block (does not include
 341                                    this trailer).  */
 342     long unknown2;
 343     long unknown3;
 344     long link;                  /* Address of trailer block of previous
 345                                    segment.  */
 346     long unknown5;
 347     long unknown6;
 348     long unknown7;
 349     long unknown8;
 350     long unknown9;
 351     long unknown10;
 352     long unknown11;
 353     long unknown12;
 354     long unknown13;
 355     long unknown14;
 356   };
 357
 358 #    endif /* CRAY2 */
 359 #   endif /* not CRAY_STACK */
 360
 361 #   ifdef CRAY2
 362 /* Determine a "stack measure" for an arbitrary ADDRESS.
 363    I doubt that "lint" will like this much.  */
 364
 365 static long
 366 i00afunc (long *address)
 367 {
 368   struct stk_stat status;
 369   struct stk_trailer *trailer;
 370   long *block, size;
 371   long result = 0;
 372
 373   /* We want to iterate through all of the segments.  The first
 374      step is to get the stack status structure.  We could do this
 375      more quickly and more directly, perhaps, by referencing the
 376      $LM00 common block, but I know that this works.  */
 377
 378   STKSTAT (&status);
 379
 380   /* Set up the iteration.  */
 381
 382   trailer = (struct stk_trailer *) (status.current_address
 383                                     + status.current_size
 384                                     - 15);
 385
 386   /* There must be at least one stack segment.  Therefore it is
 387      a fatal error if "trailer" is null.  */
 388
 389   if (trailer == 0)
 390     abort ();
 391
 392   /* Discard segments that do not contain our argument address.  */
 393
 394   while (trailer != 0)
 395     {
 396       block = (long *) trailer->this_address;
 397       size = trailer->this_size;
 398       if (block == 0 || size == 0)
 399         abort ();
 400       trailer = (struct stk_trailer *) trailer->link;
 401       if ((block <= address) && (address < (block + size)))
 402         break;
 403     }
 404
 405   /* Set the result to the offset in this segment and add the sizes
 406      of all predecessor segments.  */
 407
 408   result = address - block;
 409
 410   if (trailer == 0)
 411     {
 412       return result;
 413     }
 414
 415   do
 416     {
 417       if (trailer->this_size <= 0)
 418         abort ();
 419       result += trailer->this_size;
 420       trailer = (struct stk_trailer *) trailer->link;
 421     }
 422   while (trailer != 0);
 423
 424   /* We are done.  Note that if you present a bogus address (one
 425      not in any segment), you will get a different number back, formed
 426      from subtracting the address of the first block.  This is probably
 427      not what you want.  */
 428
 429   return (result);
 430 }
 431
 432 #   else /* not CRAY2 */
 433 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
 434    Determine the number of the cell within the stack,
 435    given the address of the cell.  The purpose of this
 436    routine is to linearize, in some sense, stack addresses
 437    for alloca.  */
 438
 439 static long
 440 i00afunc (long address)
 441 {
 442   long stkl = 0;
 443
 444   long size, pseg, this_segment, stack;
 445   long result = 0;
 446
 447   struct stack_segment_linkage *ssptr;
 448
 449   /* Register B67 contains the address of the end of the
 450      current stack segment.  If you (as a subprogram) store
 451      your registers on the stack and find that you are past
 452      the contents of B67, you have overflowed the segment.
 453
 454      B67 also points to the stack segment linkage control
 455      area, which is what we are really interested in.  */
 456
 457   stkl = CRAY_STACKSEG_END ();
 458   ssptr = (struct stack_segment_linkage *) stkl;
 459
 460   /* If one subtracts 'size' from the end of the segment,
 461      one has the address of the first word of the segment.
 462
 463      If this is not the first segment, 'pseg' will be
 464      nonzero.  */
 465
 466   pseg = ssptr->sspseg;
 467   size = ssptr->sssize;
 468
 469   this_segment = stkl - size;
 470
 471   /* It is possible that calling this routine itself caused
 472      a stack overflow.  Discard stack segments which do not
 473      contain the target address.  */
 474
 475   while (!(this_segment <= address && address <= stkl))
 476     {
 477 #    ifdef DEBUG_I00AFUNC
 478       fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
 479 #    endif
 480       if (pseg == 0)
 481         break;
 482       stkl = stkl - pseg;
 483       ssptr = (struct stack_segment_linkage *) stkl;
 484       size = ssptr->sssize;
 485       pseg = ssptr->sspseg;
 486       this_segment = stkl - size;
 487     }
 488
 489   result = address - this_segment;
 490
 491   /* If you subtract pseg from the current end of the stack,
 492      you get the address of the previous stack segment's end.
 493      This seems a little convoluted to me, but I'll bet you save
 494      a cycle somewhere.  */
 495
 496   while (pseg != 0)
 497     {
 498 #    ifdef DEBUG_I00AFUNC
 499       fprintf (stderr, "%011o %011o\n", pseg, size);
 500 #    endif
 501       stkl = stkl - pseg;
 502       ssptr = (struct stack_segment_linkage *) stkl;
 503       size = ssptr->sssize;
 504       pseg = ssptr->sspseg;
 505       result += size;
 506     }
 507   return (result);
 508 }
 509
 510 #   endif /* not CRAY2 */
 511 #  endif /* CRAY */
 512
 513 # endif /* no alloca */
 514 #endif /* not GCC version 2 */
 515
 516 /* arch-tag: 5c9901c8-3cd4-453e-bd66-d9035a175ee3
 517    (do not change this comment) */