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