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