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