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 HAVE_STRING_H
  29 #include <string.h>
  30 #endif
  31 #ifdef HAVE_STDLIB_H
  32 #include <stdlib.h>
  33 #endif
  34
  35 #ifdef emacs
  36 #include "lisp.h"
  37 #include "blockinput.h"
  38 #endif
  39
  40 /* If compiling with GCC 2, this file's not needed.  */
  41 #if !defined (__GNUC__) || __GNUC__ < 2
  42
  43 /* If someone has defined alloca as a macro,
  44    there must be some other way alloca is supposed to work.  */
  45 #ifndef alloca
  46
  47 #ifdef emacs
  48 #ifdef static
  49 /* actually, only want this if static is defined as ""
  50    -- this is for usg, in which emacs must undefine static
  51    in order to make unexec workable
  52    */
  53 #ifndef STACK_DIRECTION
  54   #error "Must know STACK_DIRECTION at compile-time"
  55 #endif /* STACK_DIRECTION undefined */
  56 #endif /* static */
  57 #endif /* emacs */
  58
  59 /* If your stack is a linked list of frames, you have to
  60    provide an "address metric" ADDRESS_FUNCTION macro.  */
  61
  62 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
  63 long i00afunc ();
  64 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
  65 #else
  66 #define ADDRESS_FUNCTION(arg) &(arg)
  67 #endif
  68
  69 #ifdef POINTER_TYPE
  70 typedef POINTER_TYPE *pointer;
  71 #else
  72 #if __STDC__
  73 typedef void *pointer;
  74 #else
  75 typedef char *pointer;
  76 #endif /*__STDC__*/
  77 #endif /*POINTER_TYPE*/
  78
  79
  80 #ifndef NULL
  81 #define NULL    0
  82 #endif
  83
  84 /* Different portions of Emacs need to call different versions of
  85    malloc.  The Emacs executable needs alloca to call xmalloc, because
  86    ordinary malloc isn't protected from input signals.  On the other
  87    hand, the utilities in lib-src need alloca to call malloc; some of
  88    them are very simple, and don't have an xmalloc routine.
  89
  90    Non-Emacs programs expect this to call use xmalloc.
  91
  92    Callers below should use malloc.  */
  93
  94 #ifdef emacs
  95 #define malloc xmalloc
  96 #ifdef EMACS_FREE
  97 #define free EMACS_FREE
  98 #endif
  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 #ifdef DEBUG_I00AFUNC
 245 #include <stdio.h>
 246 #endif
 247
 248 #ifndef CRAY_STACK
 249 #define CRAY_STACK
 250 #ifndef CRAY2
 251 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
 252 struct stack_control_header
 253   {
 254     long shgrow:32;             /* Number of times stack has grown.  */
 255     long shaseg:32;             /* Size of increments to stack.  */
 256     long shhwm:32;              /* High water mark of stack.  */
 257     long shsize:32;             /* Current size of stack (all segments).  */
 258   };
 259
 260 /* The stack segment linkage control information occurs at
 261    the high-address end of a stack segment.  (The stack
 262    grows from low addresses to high addresses.)  The initial
 263    part of the stack segment linkage control information is
 264    0200 (octal) words.  This provides for register storage
 265    for the routine which overflows the stack.  */
 266
 267 struct stack_segment_linkage
 268   {
 269     long ss[0200];              /* 0200 overflow words.  */
 270     long sssize:32;             /* Number of words in this segment.  */
 271     long ssbase:32;             /* Offset to stack base.  */
 272     long:32;
 273     long sspseg:32;             /* Offset to linkage control of previous
 274                                    segment of stack.  */
 275     long:32;
 276     long sstcpt:32;             /* Pointer to task common address block.  */
 277     long sscsnm;                /* Private control structure number for
 278                                    microtasking.  */
 279     long ssusr1;                /* Reserved for user.  */
 280     long ssusr2;                /* Reserved for user.  */
 281     long sstpid;                /* Process ID for pid based multi-tasking.  */
 282     long ssgvup;                /* Pointer to multitasking thread giveup.  */
 283     long sscray[7];             /* Reserved for Cray Research.  */
 284     long ssa0;
 285     long ssa1;
 286     long ssa2;
 287     long ssa3;
 288     long ssa4;
 289     long ssa5;
 290     long ssa6;
 291     long ssa7;
 292     long sss0;
 293     long sss1;
 294     long sss2;
 295     long sss3;
 296     long sss4;
 297     long sss5;
 298     long sss6;
 299     long sss7;
 300   };
 301
 302 #else /* CRAY2 */
 303 /* The following structure defines the vector of words
 304    returned by the STKSTAT library routine.  */
 305 struct stk_stat
 306   {
 307     long now;                   /* Current total stack size.  */
 308     long maxc;                  /* Amount of contiguous space which would
 309                                    be required to satisfy the maximum
 310                                    stack demand to date.  */
 311     long high_water;            /* Stack high-water mark.  */
 312     long overflows;             /* Number of stack overflow ($STKOFEN) calls.  */
 313     long hits;                  /* Number of internal buffer hits.  */
 314     long extends;               /* Number of block extensions.  */
 315     long stko_mallocs;          /* Block allocations by $STKOFEN.  */
 316     long underflows;            /* Number of stack underflow calls ($STKRETN).  */
 317     long stko_free;             /* Number of deallocations by $STKRETN.  */
 318     long stkm_free;             /* Number of deallocations by $STKMRET.  */
 319     long segments;              /* Current number of stack segments.  */
 320     long maxs;                  /* Maximum number of stack segments so far.  */
 321     long pad_size;              /* Stack pad size.  */
 322     long current_address;       /* Current stack segment address.  */
 323     long current_size;          /* Current stack segment size.  This
 324                                    number is actually corrupted by STKSTAT to
 325                                    include the fifteen word trailer area.  */
 326     long initial_address;       /* Address of initial segment.  */
 327     long initial_size;          /* Size of initial segment.  */
 328   };
 329
 330 /* The following structure describes the data structure which trails
 331    any stack segment.  I think that the description in 'asdef' is
 332    out of date.  I only describe the parts that I am sure about.  */
 333
 334 struct stk_trailer
 335   {
 336     long this_address;          /* Address of this block.  */
 337     long this_size;             /* Size of this block (does not include
 338                                    this trailer).  */
 339     long unknown2;
 340     long unknown3;
 341     long link;                  /* Address of trailer block of previous
 342                                    segment.  */
 343     long unknown5;
 344     long unknown6;
 345     long unknown7;
 346     long unknown8;
 347     long unknown9;
 348     long unknown10;
 349     long unknown11;
 350     long unknown12;
 351     long unknown13;
 352     long unknown14;
 353   };
 354
 355 #endif /* CRAY2 */
 356 #endif /* not CRAY_STACK */
 357
 358 #ifdef CRAY2
 359 /* Determine a "stack measure" for an arbitrary ADDRESS.
 360    I doubt that "lint" will like this much.  */
 361
 362 static long
 363 i00afunc (long *address)
 364 {
 365   struct stk_stat status;
 366   struct stk_trailer *trailer;
 367   long *block, size;
 368   long result = 0;
 369
 370   /* We want to iterate through all of the segments.  The first
 371      step is to get the stack status structure.  We could do this
 372      more quickly and more directly, perhaps, by referencing the
 373      $LM00 common block, but I know that this works.  */
 374
 375   STKSTAT (&status);
 376
 377   /* Set up the iteration.  */
 378
 379   trailer = (struct stk_trailer *) (status.current_address
 380                                     + status.current_size
 381                                     - 15);
 382
 383   /* There must be at least one stack segment.  Therefore it is
 384      a fatal error if "trailer" is null.  */
 385
 386   if (trailer == 0)
 387     abort ();
 388
 389   /* Discard segments that do not contain our argument address.  */
 390
 391   while (trailer != 0)
 392     {
 393       block = (long *) trailer->this_address;
 394       size = trailer->this_size;
 395       if (block == 0 || size == 0)
 396         abort ();
 397       trailer = (struct stk_trailer *) trailer->link;
 398       if ((block <= address) && (address < (block + size)))
 399         break;
 400     }
 401
 402   /* Set the result to the offset in this segment and add the sizes
 403      of all predecessor segments.  */
 404
 405   result = address - block;
 406
 407   if (trailer == 0)
 408     {
 409       return result;
 410     }
 411
 412   do
 413     {
 414       if (trailer->this_size <= 0)
 415         abort ();
 416       result += trailer->this_size;
 417       trailer = (struct stk_trailer *) trailer->link;
 418     }
 419   while (trailer != 0);
 420
 421   /* We are done.  Note that if you present a bogus address (one
 422      not in any segment), you will get a different number back, formed
 423      from subtracting the address of the first block.  This is probably
 424      not what you want.  */
 425
 426   return (result);
 427 }
 428
 429 #else /* not CRAY2 */
 430 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
 431    Determine the number of the cell within the stack,
 432    given the address of the cell.  The purpose of this
 433    routine is to linearize, in some sense, stack addresses
 434    for alloca.  */
 435
 436 static long
 437 i00afunc (long address)
 438 {
 439   long stkl = 0;
 440
 441   long size, pseg, this_segment, stack;
 442   long result = 0;
 443
 444   struct stack_segment_linkage *ssptr;
 445
 446   /* Register B67 contains the address of the end of the
 447      current stack segment.  If you (as a subprogram) store
 448      your registers on the stack and find that you are past
 449      the contents of B67, you have overflowed the segment.
 450
 451      B67 also points to the stack segment linkage control
 452      area, which is what we are really interested in.  */
 453
 454   stkl = CRAY_STACKSEG_END ();
 455   ssptr = (struct stack_segment_linkage *) stkl;
 456
 457   /* If one subtracts 'size' from the end of the segment,
 458      one has the address of the first word of the segment.
 459
 460      If this is not the first segment, 'pseg' will be
 461      nonzero.  */
 462
 463   pseg = ssptr->sspseg;
 464   size = ssptr->sssize;
 465
 466   this_segment = stkl - size;
 467
 468   /* It is possible that calling this routine itself caused
 469      a stack overflow.  Discard stack segments which do not
 470      contain the target address.  */
 471
 472   while (!(this_segment <= address && address <= stkl))
 473     {
 474 #ifdef DEBUG_I00AFUNC
 475       fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
 476 #endif
 477       if (pseg == 0)
 478         break;
 479       stkl = stkl - pseg;
 480       ssptr = (struct stack_segment_linkage *) stkl;
 481       size = ssptr->sssize;
 482       pseg = ssptr->sspseg;
 483       this_segment = stkl - size;
 484     }
 485
 486   result = address - this_segment;
 487
 488   /* If you subtract pseg from the current end of the stack,
 489      you get the address of the previous stack segment's end.
 490      This seems a little convoluted to me, but I'll bet you save
 491      a cycle somewhere.  */
 492
 493   while (pseg != 0)
 494     {
 495 #ifdef DEBUG_I00AFUNC
 496       fprintf (stderr, "%011o %011o\n", pseg, size);
 497 #endif
 498       stkl = stkl - pseg;
 499       ssptr = (struct stack_segment_linkage *) stkl;
 500       size = ssptr->sssize;
 501       pseg = ssptr->sspseg;
 502       result += size;
 503     }
 504   return (result);
 505 }
 506
 507 #endif /* not CRAY2 */
 508 #endif /* CRAY */
 509
 510 #endif /* no alloca */
 511 #endif /* not GCC version 2 */