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