libs/alloca.c

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