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