libs/alloca.c

   1 /* This program is free software; you can redistribute it and/or modify
   2  * it under the terms of the GNU General Public License as published by
   3  * the Free Software Foundation; either version 2 of the License, or
   4  * (at your option) any later version.
   5  *
   6  * This program is distributed in the hope that it will be useful,
   7  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   8  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   9  * GNU General Public License for more details.
  10  *
  11  * You should have received a copy of the GNU General Public License
  12  * along with this program; if not, write to the Free Software
  13  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  14  */
  15
  16 /* alloca.c -- allocate automatically reclaimed memory
  17    (Mostly) portable public-domain implementation -- D A Gwyn
  18
  19    This implementation of the PWB library alloca function,
  20    which is used to allocate space off the run-time stack so
  21    that it is automatically reclaimed upon procedure exit,
  22    was inspired by discussions with J. Q. Johnson of Cornell.
  23    J.Otto Tennant <jot@cray.com> contributed the Cray support.
  24
  25    There are some preprocessor constants that can
  26    be defined when compiling for your specific system, for
  27    improved efficiency; however, the defaults should be okay.
  28
  29    The general concept of this implementation is to keep
  30    track of all alloca-allocated blocks, and reclaim any
  31    that are found to be deeper in the stack than the current
  32    invocation.  This heuristic does not reclaim storage as
  33    soon as it becomes invalid, but it will do so eventually.
  34
  35    As a special case, alloca(0) reclaims storage without
  36    allocating any.  It is a good idea to use alloca(0) in
  37    your main control loop, etc. to force garbage collection.  */
  38
  39 #ifdef HAVE_CONFIG_H
  40 #include <config.h>
  41 #endif
  42
  43 #ifdef HAVE_STRING_H
  44 #include <string.h>
  45 #endif
  46 #ifdef HAVE_STDLIB_H
  47 #include <stdlib.h>
  48 #endif
  49
  50 #ifdef emacs
  51 #include "blockinput.h"
  52 #endif
  53
  54 /* If compiling with GCC 2, this file's not needed.  */
  55 #if !defined (__GNUC__) || __GNUC__ < 2
  56
  57 /* If someone has defined alloca as a macro,
  58    there must be some other way alloca is supposed to work.  */
  59 #ifndef alloca
  60
  61 #ifdef emacs
  62 #ifdef static
  63 /* actually, only want this if static is defined as ""
  64    -- this is for usg, in which emacs must undefine static
  65    in order to make unexec workable
  66    */
  67 #ifndef STACK_DIRECTION
  68 you
  69 lose
  70 -- must know STACK_DIRECTION at compile-time
  71 #endif /* STACK_DIRECTION undefined */
  72 #endif /* static */
  73 #endif /* emacs */
  74
  75 /* If your stack is a linked list of frames, you have to
  76    provide an "address metric" ADDRESS_FUNCTION macro.  */
  77
  78 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
  79 long i00afunc ();
  80 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
  81 #else
  82 #define ADDRESS_FUNCTION(arg) &(arg)
  83 #endif
  84
  85 #if __STDC__
  86 typedef void *pointer;
  87 #else
  88 typedef char *pointer;
  89 #endif
  90
  91 #ifndef NULL
  92 #define NULL    0
  93 #endif
  94
  95 /* Different portions of Emacs need to call different versions of
  96    malloc.  The Emacs executable needs alloca to call xmalloc, because
  97    ordinary malloc isn't protected from input signals.  On the other
  98    hand, the utilities in lib-src need alloca to call malloc; some of
  99    them are very simple, and don't have an xmalloc routine.
 100
 101    Non-Emacs programs expect this to call use xmalloc.
 102
 103    Callers below should use malloc.  */
 104
 105 #ifndef emacs
 106 #define malloc xmalloc
 107 #endif
 108 extern pointer malloc ();
 109
 110 /* Define STACK_DIRECTION if you know the direction of stack
 111    growth for your system; otherwise it will be automatically
 112    deduced at run-time.
 113
 114    STACK_DIRECTION > 0 => grows toward higher addresses
 115    STACK_DIRECTION < 0 => grows toward lower addresses
 116    STACK_DIRECTION = 0 => direction of growth unknown  */
 117
 118 #ifndef STACK_DIRECTION
 119 #define STACK_DIRECTION 0       /* Direction unknown.  */
 120 #endif
 121
 122 #if STACK_DIRECTION != 0
 123
 124 #define STACK_DIR       STACK_DIRECTION /* Known at compile-time.  */
 125
 126 #else /* STACK_DIRECTION == 0; need run-time code.  */
 127
 128 static int stack_dir;           /* 1 or -1 once known.  */
 129 #define STACK_DIR       stack_dir
 130
 131 static void
 132 find_stack_direction ()
 133 {
 134   static char *addr = NULL;     /* Address of first `dummy', once known.  */
 135   auto char dummy;              /* To get stack address.  */
 136
 137   if (addr == NULL)
 138     {                           /* Initial entry.  */
 139       addr = ADDRESS_FUNCTION (dummy);
 140
 141       find_stack_direction ();  /* Recurse once.  */
 142     }
 143   else
 144     {
 145       /* Second entry.  */
 146       if (ADDRESS_FUNCTION (dummy) > addr)
 147         stack_dir = 1;          /* Stack grew upward.  */
 148       else
 149         stack_dir = -1;         /* Stack grew downward.  */
 150     }
 151 }
 152
 153 #endif /* STACK_DIRECTION == 0 */
 154
 155 /* An "alloca header" is used to:
 156    (a) chain together all alloca'ed blocks;
 157    (b) keep track of stack depth.
 158
 159    It is very important that sizeof(header) agree with malloc
 160    alignment chunk size.  The following default should work okay.  */
 161
 162 #ifndef ALIGN_SIZE
 163 #define ALIGN_SIZE      sizeof(double)
 164 #endif
 165
 166 typedef union hdr
 167 {
 168   char align[ALIGN_SIZE];       /* To force sizeof(header).  */
 169   struct
 170     {
 171       union hdr *next;          /* For chaining headers.  */
 172       char *deep;               /* For stack depth measure.  */
 173     } h;
 174 } header;
 175
 176 static header *last_alloca_header = NULL;       /* -> last alloca header.  */
 177
 178 /* Return a pointer to at least SIZE bytes of storage,
 179    which will be automatically reclaimed upon exit from
 180    the procedure that called alloca.  Originally, this space
 181    was supposed to be taken from the current stack frame of the
 182    caller, but that method cannot be made to work for some
 183    implementations of C, for example under Gould's UTX/32.  */
 184
 185 pointer
 186 alloca (size)
 187      unsigned size;
 188 {
 189   auto char probe;              /* Probes stack depth: */
 190   register char *depth = ADDRESS_FUNCTION (probe);
 191
 192 #if STACK_DIRECTION == 0
 193   if (STACK_DIR == 0)           /* Unknown growth direction.  */
 194     find_stack_direction ();
 195 #endif
 196
 197   /* Reclaim garbage, defined as all alloca'd storage that
 198      was allocated from deeper in the stack than currently.  */
 199
 200   {
 201     register header *hp;        /* Traverses linked list.  */
 202
 203 #ifdef emacs
 204     BLOCK_INPUT;
 205 #endif
 206
 207     for (hp = last_alloca_header; hp != NULL;)
 208       if ((STACK_DIR > 0 && hp->h.deep > depth)
 209           || (STACK_DIR < 0 && hp->h.deep < depth))
 210         {
 211           register header *np = hp->h.next;
 212
 213           free ((pointer) hp);  /* Collect garbage.  */
 214
 215           hp = np;              /* -> next header.  */
 216         }
 217       else
 218         break;                  /* Rest are not deeper.  */
 219
 220     last_alloca_header = hp;    /* -> last valid storage.  */
 221
 222 #ifdef emacs
 223     UNBLOCK_INPUT;
 224 #endif
 225   }
 226
 227   if (size == 0)
 228     return NULL;                /* No allocation required.  */
 229
 230   /* Allocate combined header + user data storage.  */
 231
 232   {
 233     register pointer new = malloc (sizeof (header) + size);
 234     /* Address of header.  */
 235
 236     if (new == 0)
 237       abort();
 238
 239     ((header *) new)->h.next = last_alloca_header;
 240     ((header *) new)->h.deep = depth;
 241
 242     last_alloca_header = (header *) new;
 243
 244     /* User storage begins just after header.  */
 245
 246     return (pointer) ((char *) new + sizeof (header));
 247   }
 248 }
 249
 250 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
 251
 252 #ifdef DEBUG_I00AFUNC
 253 #include <stdio.h>
 254 #endif
 255
 256 #ifndef CRAY_STACK
 257 #define CRAY_STACK
 258 #ifndef CRAY2
 259 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
 260 struct stack_control_header
 261   {
 262     long shgrow:32;             /* Number of times stack has grown.  */
 263     long shaseg:32;             /* Size of increments to stack.  */
 264     long shhwm:32;              /* High water mark of stack.  */
 265     long shsize:32;             /* Current size of stack (all segments).  */
 266   };
 267
 268 /* The stack segment linkage control information occurs at
 269    the high-address end of a stack segment.  (The stack
 270    grows from low addresses to high addresses.)  The initial
 271    part of the stack segment linkage control information is
 272    0200 (octal) words.  This provides for register storage
 273    for the routine which overflows the stack.  */
 274
 275 struct stack_segment_linkage
 276   {
 277     long ss[0200];              /* 0200 overflow words.  */
 278     long sssize:32;             /* Number of words in this segment.  */
 279     long ssbase:32;             /* Offset to stack base.  */
 280     long:32;
 281     long sspseg:32;             /* Offset to linkage control of previous
 282                                    segment of stack.  */
 283     long:32;
 284     long sstcpt:32;             /* Pointer to task common address block.  */
 285     long sscsnm;                /* Private control structure number for
 286                                    microtasking.  */
 287     long ssusr1;                /* Reserved for user.  */
 288     long ssusr2;                /* Reserved for user.  */
 289     long sstpid;                /* Process ID for pid based multi-tasking.  */
 290     long ssgvup;                /* Pointer to multitasking thread giveup.  */
 291     long sscray[7];             /* Reserved for Cray Research.  */
 292     long ssa0;
 293     long ssa1;
 294     long ssa2;
 295     long ssa3;
 296     long ssa4;
 297     long ssa5;
 298     long ssa6;
 299     long ssa7;
 300     long sss0;
 301     long sss1;
 302     long sss2;
 303     long sss3;
 304     long sss4;
 305     long sss5;
 306     long sss6;
 307     long sss7;
 308   };
 309
 310 #else /* CRAY2 */
 311 /* The following structure defines the vector of words
 312    returned by the STKSTAT library routine.  */
 313 struct stk_stat
 314   {
 315     long now;                   /* Current total stack size.  */
 316     long maxc;                  /* Amount of contiguous space which would
 317                                    be required to satisfy the maximum
 318                                    stack demand to date.  */
 319     long high_water;            /* Stack high-water mark.  */
 320     long overflows;             /* Number of stack overflow ($STKOFEN) calls.  */
 321     long hits;                  /* Number of internal buffer hits.  */
 322     long extends;               /* Number of block extensions.  */
 323     long stko_mallocs;          /* Block allocations by $STKOFEN.  */
 324     long underflows;            /* Number of stack underflow calls ($STKRETN).  */
 325     long stko_free;             /* Number of deallocations by $STKRETN.  */
 326     long stkm_free;             /* Number of deallocations by $STKMRET.  */
 327     long segments;              /* Current number of stack segments.  */
 328     long maxs;                  /* Maximum number of stack segments so far.  */
 329     long pad_size;              /* Stack pad size.  */
 330     long current_address;       /* Current stack segment address.  */
 331     long current_size;          /* Current stack segment size.  This
 332                                    number is actually corrupted by STKSTAT to
 333                                    include the fifteen word trailer area.  */
 334     long initial_address;       /* Address of initial segment.  */
 335     long initial_size;          /* Size of initial segment.  */
 336   };
 337
 338 /* The following structure describes the data structure which trails
 339    any stack segment.  I think that the description in 'asdef' is
 340    out of date.  I only describe the parts that I am sure about.  */
 341
 342 struct stk_trailer
 343   {
 344     long this_address;          /* Address of this block.  */
 345     long this_size;             /* Size of this block (does not include
 346                                    this trailer).  */
 347     long unknown2;
 348     long unknown3;
 349     long link;                  /* Address of trailer block of previous
 350                                    segment.  */
 351     long unknown5;
 352     long unknown6;
 353     long unknown7;
 354     long unknown8;
 355     long unknown9;
 356     long unknown10;
 357     long unknown11;
 358     long unknown12;
 359     long unknown13;
 360     long unknown14;
 361   };
 362
 363 #endif /* CRAY2 */
 364 #endif /* not CRAY_STACK */
 365
 366 #ifdef CRAY2
 367 /* Determine a "stack measure" for an arbitrary ADDRESS.
 368    I doubt that "lint" will like this much.  */
 369
 370 static long
 371 i00afunc (long *address)
 372 {
 373   struct stk_stat status;
 374   struct stk_trailer *trailer;
 375   long *block, size;
 376   long result = 0;
 377
 378   /* We want to iterate through all of the segments.  The first
 379      step is to get the stack status structure.  We could do this
 380      more quickly and more directly, perhaps, by referencing the
 381      $LM00 common block, but I know that this works.  */
 382
 383   STKSTAT (&status);
 384
 385   /* Set up the iteration.  */
 386
 387   trailer = (struct stk_trailer *) (status.current_address
 388                                     + status.current_size
 389                                     - 15);
 390
 391   /* There must be at least one stack segment.  Therefore it is
 392      a fatal error if "trailer" is null.  */
 393
 394   if (trailer == 0)
 395     abort ();
 396
 397   /* Discard segments that do not contain our argument address.  */
 398
 399   while (trailer != 0)
 400     {
 401       block = (long *) trailer->this_address;
 402       size = trailer->this_size;
 403       if (block == 0 || size == 0)
 404         abort ();
 405       trailer = (struct stk_trailer *) trailer->link;
 406       if ((block <= address) && (address < (block + size)))
 407         break;
 408     }
 409
 410   /* Set the result to the offset in this segment and add the sizes
 411      of all predecessor segments.  */
 412
 413   result = address - block;
 414
 415   if (trailer == 0)
 416     {
 417       return result;
 418     }
 419
 420   do
 421     {
 422       if (trailer->this_size <= 0)
 423         abort ();
 424       result += trailer->this_size;
 425       trailer = (struct stk_trailer *) trailer->link;
 426     }
 427   while (trailer != 0);
 428
 429   /* We are done.  Note that if you present a bogus address (one
 430      not in any segment), you will get a different number back, formed
 431      from subtracting the address of the first block.  This is probably
 432      not what you want.  */
 433
 434   return (result);
 435 }
 436
 437 #else /* not CRAY2 */
 438 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
 439    Determine the number of the cell within the stack,
 440    given the address of the cell.  The purpose of this
 441    routine is to linearize, in some sense, stack addresses
 442    for alloca.  */
 443
 444 static long
 445 i00afunc (long address)
 446 {
 447   long stkl = 0;
 448
 449   long size, pseg, this_segment, stack;
 450   long result = 0;
 451
 452   struct stack_segment_linkage *ssptr;
 453
 454   /* Register B67 contains the address of the end of the
 455      current stack segment.  If you (as a subprogram) store
 456      your registers on the stack and find that you are past
 457      the contents of B67, you have overflowed the segment.
 458
 459      B67 also points to the stack segment linkage control
 460      area, which is what we are really interested in.  */
 461
 462   stkl = CRAY_STACKSEG_END ();
 463   ssptr = (struct stack_segment_linkage *) stkl;
 464
 465   /* If one subtracts 'size' from the end of the segment,
 466      one has the address of the first word of the segment.
 467
 468      If this is not the first segment, 'pseg' will be
 469      nonzero.  */
 470
 471   pseg = ssptr->sspseg;
 472   size = ssptr->sssize;
 473
 474   this_segment = stkl - size;
 475
 476   /* It is possible that calling this routine itself caused
 477      a stack overflow.  Discard stack segments which do not
 478      contain the target address.  */
 479
 480   while (!(this_segment <= address && address <= stkl))
 481     {
 482 #ifdef DEBUG_I00AFUNC
 483       fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
 484 #endif
 485       if (pseg == 0)
 486         break;
 487       stkl = stkl - pseg;
 488       ssptr = (struct stack_segment_linkage *) stkl;
 489       size = ssptr->sssize;
 490       pseg = ssptr->sspseg;
 491       this_segment = stkl - size;
 492     }
 493
 494   result = address - this_segment;
 495
 496   /* If you subtract pseg from the current end of the stack,
 497      you get the address of the previous stack segment's end.
 498      This seems a little convoluted to me, but I'll bet you save
 499      a cycle somewhere.  */
 500
 501   while (pseg != 0)
 502     {
 503 #ifdef DEBUG_I00AFUNC
 504       fprintf (stderr, "%011o %011o\n", pseg, size);
 505 #endif
 506       stkl = stkl - pseg;
 507       ssptr = (struct stack_segment_linkage *) stkl;
 508       size = ssptr->sssize;
 509       pseg = ssptr->sspseg;
 510       result += size;
 511     }
 512   return (result);
 513 }
 514
 515 #endif /* not CRAY2 */
 516 #endif /* CRAY */
 517
 518 #endif /* no alloca */
 519 #endif /* not GCC version 2 */