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