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 (size)
 165      unsigned size;
 166 {
 167   auto char probe;              /* Probes stack depth: */
 168   register char *depth = ADDRESS_FUNCTION (probe);
 169
 170 #  if STACK_DIRECTION == 0
 171   if (STACK_DIR == 0)           /* Unknown growth direction.  */
 172     find_stack_direction ();
 173 #  endif
 174
 175   /* Reclaim garbage, defined as all alloca'd storage that
 176      was allocated from deeper in the stack than currently.  */
 177
 178   {
 179     register header *hp;        /* Traverses linked list.  */
 180
 181 #  ifdef emacs
 182     BLOCK_INPUT;
 183 #  endif
 184
 185     for (hp = last_alloca_header; hp != NULL;)
 186       if ((STACK_DIR > 0 && hp->h.deep > depth)
 187           || (STACK_DIR < 0 && hp->h.deep < depth))
 188         {
 189           register header *np = hp->h.next;
 190
 191           free ((pointer) hp);  /* Collect garbage.  */
 192
 193           hp = np;              /* -> next header.  */
 194         }
 195       else
 196         break;                  /* Rest are not deeper.  */
 197
 198     last_alloca_header = hp;    /* -> last valid storage.  */
 199
 200 #  ifdef emacs
 201     UNBLOCK_INPUT;
 202 #  endif
 203   }
 204
 205   if (size == 0)
 206     return NULL;                /* No allocation required.  */
 207
 208   /* Allocate combined header + user data storage.  */
 209
 210   {
 211     register pointer new = malloc (sizeof (header) + size);
 212     /* Address of header.  */
 213
 214     ((header *) new)->h.next = last_alloca_header;
 215     ((header *) new)->h.deep = depth;
 216
 217     last_alloca_header = (header *) new;
 218
 219     /* User storage begins just after header.  */
 220
 221     return (pointer) ((char *) new + sizeof (header));
 222   }
 223 }
 224
 225 #  if defined (CRAY) && defined (CRAY_STACKSEG_END)
 226
 227 #   ifdef DEBUG_I00AFUNC
 228 #    include <stdio.h>
 229 #   endif
 230
 231 #   ifndef CRAY_STACK
 232 #    define CRAY_STACK
 233 #    ifndef CRAY2
 234 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
 235 struct stack_control_header
 236   {
 237     long shgrow:32;             /* Number of times stack has grown.  */
 238     long shaseg:32;             /* Size of increments to stack.  */
 239     long shhwm:32;              /* High water mark of stack.  */
 240     long shsize:32;             /* Current size of stack (all segments).  */
 241   };
 242
 243 /* The stack segment linkage control information occurs at
 244    the high-address end of a stack segment.  (The stack
 245    grows from low addresses to high addresses.)  The initial
 246    part of the stack segment linkage control information is
 247    0200 (octal) words.  This provides for register storage
 248    for the routine which overflows the stack.  */
 249
 250 struct stack_segment_linkage
 251   {
 252     long ss[0200];              /* 0200 overflow words.  */
 253     long sssize:32;             /* Number of words in this segment.  */
 254     long ssbase:32;             /* Offset to stack base.  */
 255     long:32;
 256     long sspseg:32;             /* Offset to linkage control of previous
 257                                    segment of stack.  */
 258     long:32;
 259     long sstcpt:32;             /* Pointer to task common address block.  */
 260     long sscsnm;                /* Private control structure number for
 261                                    microtasking.  */
 262     long ssusr1;                /* Reserved for user.  */
 263     long ssusr2;                /* Reserved for user.  */
 264     long sstpid;                /* Process ID for pid based multi-tasking.  */
 265     long ssgvup;                /* Pointer to multitasking thread giveup.  */
 266     long sscray[7];             /* Reserved for Cray Research.  */
 267     long ssa0;
 268     long ssa1;
 269     long ssa2;
 270     long ssa3;
 271     long ssa4;
 272     long ssa5;
 273     long ssa6;
 274     long ssa7;
 275     long sss0;
 276     long sss1;
 277     long sss2;
 278     long sss3;
 279     long sss4;
 280     long sss5;
 281     long sss6;
 282     long sss7;
 283   };
 284
 285 #    else /* CRAY2 */
 286 /* The following structure defines the vector of words
 287    returned by the STKSTAT library routine.  */
 288 struct stk_stat
 289   {
 290     long now;                   /* Current total stack size.  */
 291     long maxc;                  /* Amount of contiguous space which would
 292                                    be required to satisfy the maximum
 293                                    stack demand to date.  */
 294     long high_water;            /* Stack high-water mark.  */
 295     long overflows;             /* Number of stack overflow ($STKOFEN) calls.  */
 296     long hits;                  /* Number of internal buffer hits.  */
 297     long extends;               /* Number of block extensions.  */
 298     long stko_mallocs;          /* Block allocations by $STKOFEN.  */
 299     long underflows;            /* Number of stack underflow calls ($STKRETN).  */
 300     long stko_free;             /* Number of deallocations by $STKRETN.  */
 301     long stkm_free;             /* Number of deallocations by $STKMRET.  */
 302     long segments;              /* Current number of stack segments.  */
 303     long maxs;                  /* Maximum number of stack segments so far.  */
 304     long pad_size;              /* Stack pad size.  */
 305     long current_address;       /* Current stack segment address.  */
 306     long current_size;          /* Current stack segment size.  This
 307                                    number is actually corrupted by STKSTAT to
 308                                    include the fifteen word trailer area.  */
 309     long initial_address;       /* Address of initial segment.  */
 310     long initial_size;          /* Size of initial segment.  */
 311   };
 312
 313 /* The following structure describes the data structure which trails
 314    any stack segment.  I think that the description in 'asdef' is
 315    out of date.  I only describe the parts that I am sure about.  */
 316
 317 struct stk_trailer
 318   {
 319     long this_address;          /* Address of this block.  */
 320     long this_size;             /* Size of this block (does not include
 321                                    this trailer).  */
 322     long unknown2;
 323     long unknown3;
 324     long link;                  /* Address of trailer block of previous
 325                                    segment.  */
 326     long unknown5;
 327     long unknown6;
 328     long unknown7;
 329     long unknown8;
 330     long unknown9;
 331     long unknown10;
 332     long unknown11;
 333     long unknown12;
 334     long unknown13;
 335     long unknown14;
 336   };
 337
 338 #    endif /* CRAY2 */
 339 #   endif /* not CRAY_STACK */
 340
 341 #   ifdef CRAY2
 342 /* Determine a "stack measure" for an arbitrary ADDRESS.
 343    I doubt that "lint" will like this much.  */
 344
 345 static long
 346 i00afunc (long *address)
 347 {
 348   struct stk_stat status;
 349   struct stk_trailer *trailer;
 350   long *block, size;
 351   long result = 0;
 352
 353   /* We want to iterate through all of the segments.  The first
 354      step is to get the stack status structure.  We could do this
 355      more quickly and more directly, perhaps, by referencing the
 356      $LM00 common block, but I know that this works.  */
 357
 358   STKSTAT (&status);
 359
 360   /* Set up the iteration.  */
 361
 362   trailer = (struct stk_trailer *) (status.current_address
 363                                     + status.current_size
 364                                     - 15);
 365
 366   /* There must be at least one stack segment.  Therefore it is
 367      a fatal error if "trailer" is null.  */
 368
 369   if (trailer == 0)
 370     abort ();
 371
 372   /* Discard segments that do not contain our argument address.  */
 373
 374   while (trailer != 0)
 375     {
 376       block = (long *) trailer->this_address;
 377       size = trailer->this_size;
 378       if (block == 0 || size == 0)
 379         abort ();
 380       trailer = (struct stk_trailer *) trailer->link;
 381       if ((block <= address) && (address < (block + size)))
 382         break;
 383     }
 384
 385   /* Set the result to the offset in this segment and add the sizes
 386      of all predecessor segments.  */
 387
 388   result = address - block;
 389
 390   if (trailer == 0)
 391     {
 392       return result;
 393     }
 394
 395   do
 396     {
 397       if (trailer->this_size <= 0)
 398         abort ();
 399       result += trailer->this_size;
 400       trailer = (struct stk_trailer *) trailer->link;
 401     }
 402   while (trailer != 0);
 403
 404   /* We are done.  Note that if you present a bogus address (one
 405      not in any segment), you will get a different number back, formed
 406      from subtracting the address of the first block.  This is probably
 407      not what you want.  */
 408
 409   return (result);
 410 }
 411
 412 #   else /* not CRAY2 */
 413 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
 414    Determine the number of the cell within the stack,
 415    given the address of the cell.  The purpose of this
 416    routine is to linearize, in some sense, stack addresses
 417    for alloca.  */
 418
 419 static long
 420 i00afunc (long address)
 421 {
 422   long stkl = 0;
 423
 424   long size, pseg, this_segment, stack;
 425   long result = 0;
 426
 427   struct stack_segment_linkage *ssptr;
 428
 429   /* Register B67 contains the address of the end of the
 430      current stack segment.  If you (as a subprogram) store
 431      your registers on the stack and find that you are past
 432      the contents of B67, you have overflowed the segment.
 433
 434      B67 also points to the stack segment linkage control
 435      area, which is what we are really interested in.  */
 436
 437   stkl = CRAY_STACKSEG_END ();
 438   ssptr = (struct stack_segment_linkage *) stkl;
 439
 440   /* If one subtracts 'size' from the end of the segment,
 441      one has the address of the first word of the segment.
 442
 443      If this is not the first segment, 'pseg' will be
 444      nonzero.  */
 445
 446   pseg = ssptr->sspseg;
 447   size = ssptr->sssize;
 448
 449   this_segment = stkl - size;
 450
 451   /* It is possible that calling this routine itself caused
 452      a stack overflow.  Discard stack segments which do not
 453      contain the target address.  */
 454
 455   while (!(this_segment <= address && address <= stkl))
 456     {
 457 #    ifdef DEBUG_I00AFUNC
 458       fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
 459 #    endif
 460       if (pseg == 0)
 461         break;
 462       stkl = stkl - pseg;
 463       ssptr = (struct stack_segment_linkage *) stkl;
 464       size = ssptr->sssize;
 465       pseg = ssptr->sspseg;
 466       this_segment = stkl - size;
 467     }
 468
 469   result = address - this_segment;
 470
 471   /* If you subtract pseg from the current end of the stack,
 472      you get the address of the previous stack segment's end.
 473      This seems a little convoluted to me, but I'll bet you save
 474      a cycle somewhere.  */
 475
 476   while (pseg != 0)
 477     {
 478 #    ifdef DEBUG_I00AFUNC
 479       fprintf (stderr, "%011o %011o\n", pseg, size);
 480 #    endif
 481       stkl = stkl - pseg;
 482       ssptr = (struct stack_segment_linkage *) stkl;
 483       size = ssptr->sssize;
 484       pseg = ssptr->sspseg;
 485       result += size;
 486     }
 487   return (result);
 488 }
 489
 490 #   endif /* not CRAY2 */
 491 #  endif /* CRAY */
 492
 493 # endif /* no alloca */
 494 #endif /* not GCC version 2 */