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