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