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 /*
  25
  26 @deftypefn Replacement void* alloca (size_t @var{size})
  27
  28 This function allocates memory which will be automatically reclaimed
  29 after the procedure exits.  The @libib{} implementation does not free
  30 the memory immediately but will do so eventually during subsequent
  31 calls to this function.  Memory is allocated using @code{xmalloc} under
  32 normal circumstances.
  33
  34 The header file @file{alloca-conf.h} can be used in conjunction with the
  35 GNU Autoconf test @code{AC_FUNC_ALLOCA} to test for and properly make
  36 available this function.  The @code{AC_FUNC_ALLOCA} test requires that
  37 client code use a block of preprocessor code to be safe (see the Autoconf
  38 manual for more); this header incorporates that logic and more, including
  39 the possibility of a GCC built-in function.
  40
  41 @end deftypefn
  42
  43 */
  44
  45 #ifdef HAVE_CONFIG_H
  46 #include <config.h>
  47 #endif
  48
  49 #include <libiberty.h>
  50
  51 #ifdef HAVE_STRING_H
  52 #include <string.h>
  53 #endif
  54 #ifdef HAVE_STDLIB_H
  55 #include <stdlib.h>
  56 #endif
  57
  58 /* These variables are used by the ASTRDUP implementation that relies
  59    on C_alloca.  */
  60 const char *libiberty_optr;
  61 char *libiberty_nptr;
  62 unsigned long libiberty_len;
  63
  64 /* If your stack is a linked list of frames, you have to
  65    provide an "address metric" ADDRESS_FUNCTION macro.  */
  66
  67 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
  68 static long i00afunc ();
  69 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
  70 #else
  71 #define ADDRESS_FUNCTION(arg) &(arg)
  72 #endif
  73
  74 #ifndef NULL
  75 #define NULL    0
  76 #endif
  77
  78 /* Define STACK_DIRECTION if you know the direction of stack
  79    growth for your system; otherwise it will be automatically
  80    deduced at run-time.
  81
  82    STACK_DIRECTION > 0 => grows toward higher addresses
  83    STACK_DIRECTION < 0 => grows toward lower addresses
  84    STACK_DIRECTION = 0 => direction of growth unknown  */
  85
  86 #ifndef STACK_DIRECTION
  87 #define STACK_DIRECTION 0       /* Direction unknown.  */
  88 #endif
  89
  90 #if STACK_DIRECTION != 0
  91
  92 #define STACK_DIR       STACK_DIRECTION /* Known at compile-time.  */
  93
  94 #else /* STACK_DIRECTION == 0; need run-time code.  */
  95
  96 static int stack_dir;           /* 1 or -1 once known.  */
  97 #define STACK_DIR       stack_dir
  98
  99 static void
 100 find_stack_direction ()
 101 {
 102   static char *addr = NULL;     /* Address of first `dummy', once known.  */
 103   auto char dummy;              /* To get stack address.  */
 104
 105   if (addr == NULL)
 106     {                           /* Initial entry.  */
 107       addr = ADDRESS_FUNCTION (dummy);
 108
 109       find_stack_direction ();  /* Recurse once.  */
 110     }
 111   else
 112     {
 113       /* Second entry.  */
 114       if (ADDRESS_FUNCTION (dummy) > addr)
 115         stack_dir = 1;          /* Stack grew upward.  */
 116       else
 117         stack_dir = -1;         /* Stack grew downward.  */
 118     }
 119 }
 120
 121 #endif /* STACK_DIRECTION == 0 */
 122
 123 /* An "alloca header" is used to:
 124    (a) chain together all alloca'ed blocks;
 125    (b) keep track of stack depth.
 126
 127    It is very important that sizeof(header) agree with malloc
 128    alignment chunk size.  The following default should work okay.  */
 129
 130 #ifndef ALIGN_SIZE
 131 #define ALIGN_SIZE      sizeof(double)
 132 #endif
 133
 134 typedef union hdr
 135 {
 136   char align[ALIGN_SIZE];       /* To force sizeof(header).  */
 137   struct
 138     {
 139       union hdr *next;          /* For chaining headers.  */
 140       char *deep;               /* For stack depth measure.  */
 141     } h;
 142 } header;
 143
 144 static header *last_alloca_header = NULL;       /* -> last alloca header.  */
 145
 146 /* Return a pointer to at least SIZE bytes of storage,
 147    which will be automatically reclaimed upon exit from
 148    the procedure that called alloca.  Originally, this space
 149    was supposed to be taken from the current stack frame of the
 150    caller, but that method cannot be made to work for some
 151    implementations of C, for example under Gould's UTX/32.  */
 152
 153 /* @undocumented C_alloca */
 154
 155 PTR
 156 C_alloca (size)
 157      size_t size;
 158 {
 159   auto char probe;              /* Probes stack depth: */
 160   register char *depth = ADDRESS_FUNCTION (probe);
 161
 162 #if STACK_DIRECTION == 0
 163   if (STACK_DIR == 0)           /* Unknown growth direction.  */
 164     find_stack_direction ();
 165 #endif
 166
 167   /* Reclaim garbage, defined as all alloca'd storage that
 168      was allocated from deeper in the stack than currently.  */
 169
 170   {
 171     register header *hp;        /* Traverses linked list.  */
 172
 173     for (hp = last_alloca_header; hp != NULL;)
 174       if ((STACK_DIR > 0 && hp->h.deep > depth)
 175           || (STACK_DIR < 0 && hp->h.deep < depth))
 176         {
 177           register header *np = hp->h.next;
 178
 179           free ((PTR) hp);      /* Collect garbage.  */
 180
 181           hp = np;              /* -> next header.  */
 182         }
 183       else
 184         break;                  /* Rest are not deeper.  */
 185
 186     last_alloca_header = hp;    /* -> last valid storage.  */
 187   }
 188
 189   if (size == 0)
 190     return NULL;                /* No allocation required.  */
 191
 192   /* Allocate combined header + user data storage.  */
 193
 194   {
 195     register PTR new = xmalloc (sizeof (header) + size);
 196     /* Address of header.  */
 197
 198     if (new == 0)
 199       abort();
 200
 201     ((header *) new)->h.next = last_alloca_header;
 202     ((header *) new)->h.deep = depth;
 203
 204     last_alloca_header = (header *) new;
 205
 206     /* User storage begins just after header.  */
 207
 208     return (PTR) ((char *) new + sizeof (header));
 209   }
 210 }
 211
 212 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
 213
 214 #ifdef DEBUG_I00AFUNC
 215 #include <stdio.h>
 216 #endif
 217
 218 #ifndef CRAY_STACK
 219 #define CRAY_STACK
 220 #ifndef CRAY2
 221 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
 222 struct stack_control_header
 223   {
 224     long shgrow:32;             /* Number of times stack has grown.  */
 225     long shaseg:32;             /* Size of increments to stack.  */
 226     long shhwm:32;              /* High water mark of stack.  */
 227     long shsize:32;             /* Current size of stack (all segments).  */
 228   };
 229
 230 /* The stack segment linkage control information occurs at
 231    the high-address end of a stack segment.  (The stack
 232    grows from low addresses to high addresses.)  The initial
 233    part of the stack segment linkage control information is
 234    0200 (octal) words.  This provides for register storage
 235    for the routine which overflows the stack.  */
 236
 237 struct stack_segment_linkage
 238   {
 239     long ss[0200];              /* 0200 overflow words.  */
 240     long sssize:32;             /* Number of words in this segment.  */
 241     long ssbase:32;             /* Offset to stack base.  */
 242     long:32;
 243     long sspseg:32;             /* Offset to linkage control of previous
 244                                    segment of stack.  */
 245     long:32;
 246     long sstcpt:32;             /* Pointer to task common address block.  */
 247     long sscsnm;                /* Private control structure number for
 248                                    microtasking.  */
 249     long ssusr1;                /* Reserved for user.  */
 250     long ssusr2;                /* Reserved for user.  */
 251     long sstpid;                /* Process ID for pid based multi-tasking.  */
 252     long ssgvup;                /* Pointer to multitasking thread giveup.  */
 253     long sscray[7];             /* Reserved for Cray Research.  */
 254     long ssa0;
 255     long ssa1;
 256     long ssa2;
 257     long ssa3;
 258     long ssa4;
 259     long ssa5;
 260     long ssa6;
 261     long ssa7;
 262     long sss0;
 263     long sss1;
 264     long sss2;
 265     long sss3;
 266     long sss4;
 267     long sss5;
 268     long sss6;
 269     long sss7;
 270   };
 271
 272 #else /* CRAY2 */
 273 /* The following structure defines the vector of words
 274    returned by the STKSTAT library routine.  */
 275 struct stk_stat
 276   {
 277     long now;                   /* Current total stack size.  */
 278     long maxc;                  /* Amount of contiguous space which would
 279                                    be required to satisfy the maximum
 280                                    stack demand to date.  */
 281     long high_water;            /* Stack high-water mark.  */
 282     long overflows;             /* Number of stack overflow ($STKOFEN) calls.  */
 283     long hits;                  /* Number of internal buffer hits.  */
 284     long extends;               /* Number of block extensions.  */
 285     long stko_mallocs;          /* Block allocations by $STKOFEN.  */
 286     long underflows;            /* Number of stack underflow calls ($STKRETN).  */
 287     long stko_free;             /* Number of deallocations by $STKRETN.  */
 288     long stkm_free;             /* Number of deallocations by $STKMRET.  */
 289     long segments;              /* Current number of stack segments.  */
 290     long maxs;                  /* Maximum number of stack segments so far.  */
 291     long pad_size;              /* Stack pad size.  */
 292     long current_address;       /* Current stack segment address.  */
 293     long current_size;          /* Current stack segment size.  This
 294                                    number is actually corrupted by STKSTAT to
 295                                    include the fifteen word trailer area.  */
 296     long initial_address;       /* Address of initial segment.  */
 297     long initial_size;          /* Size of initial segment.  */
 298   };
 299
 300 /* The following structure describes the data structure which trails
 301    any stack segment.  I think that the description in 'asdef' is
 302    out of date.  I only describe the parts that I am sure about.  */
 303
 304 struct stk_trailer
 305   {
 306     long this_address;          /* Address of this block.  */
 307     long this_size;             /* Size of this block (does not include
 308                                    this trailer).  */
 309     long unknown2;
 310     long unknown3;
 311     long link;                  /* Address of trailer block of previous
 312                                    segment.  */
 313     long unknown5;
 314     long unknown6;
 315     long unknown7;
 316     long unknown8;
 317     long unknown9;
 318     long unknown10;
 319     long unknown11;
 320     long unknown12;
 321     long unknown13;
 322     long unknown14;
 323   };
 324
 325 #endif /* CRAY2 */
 326 #endif /* not CRAY_STACK */
 327
 328 #ifdef CRAY2
 329 /* Determine a "stack measure" for an arbitrary ADDRESS.
 330    I doubt that "lint" will like this much.  */
 331
 332 static long
 333 i00afunc (long *address)
 334 {
 335   struct stk_stat status;
 336   struct stk_trailer *trailer;
 337   long *block, size;
 338   long result = 0;
 339
 340   /* We want to iterate through all of the segments.  The first
 341      step is to get the stack status structure.  We could do this
 342      more quickly and more directly, perhaps, by referencing the
 343      $LM00 common block, but I know that this works.  */
 344
 345   STKSTAT (&status);
 346
 347   /* Set up the iteration.  */
 348
 349   trailer = (struct stk_trailer *) (status.current_address
 350                                     + status.current_size
 351                                     - 15);
 352
 353   /* There must be at least one stack segment.  Therefore it is
 354      a fatal error if "trailer" is null.  */
 355
 356   if (trailer == 0)
 357     abort ();
 358
 359   /* Discard segments that do not contain our argument address.  */
 360
 361   while (trailer != 0)
 362     {
 363       block = (long *) trailer->this_address;
 364       size = trailer->this_size;
 365       if (block == 0 || size == 0)
 366         abort ();
 367       trailer = (struct stk_trailer *) trailer->link;
 368       if ((block <= address) && (address < (block + size)))
 369         break;
 370     }
 371
 372   /* Set the result to the offset in this segment and add the sizes
 373      of all predecessor segments.  */
 374
 375   result = address - block;
 376
 377   if (trailer == 0)
 378     {
 379       return result;
 380     }
 381
 382   do
 383     {
 384       if (trailer->this_size <= 0)
 385         abort ();
 386       result += trailer->this_size;
 387       trailer = (struct stk_trailer *) trailer->link;
 388     }
 389   while (trailer != 0);
 390
 391   /* We are done.  Note that if you present a bogus address (one
 392      not in any segment), you will get a different number back, formed
 393      from subtracting the address of the first block.  This is probably
 394      not what you want.  */
 395
 396   return (result);
 397 }
 398
 399 #else /* not CRAY2 */
 400 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
 401    Determine the number of the cell within the stack,
 402    given the address of the cell.  The purpose of this
 403    routine is to linearize, in some sense, stack addresses
 404    for alloca.  */
 405
 406 static long
 407 i00afunc (long address)
 408 {
 409   long stkl = 0;
 410
 411   long size, pseg, this_segment, stack;
 412   long result = 0;
 413
 414   struct stack_segment_linkage *ssptr;
 415
 416   /* Register B67 contains the address of the end of the
 417      current stack segment.  If you (as a subprogram) store
 418      your registers on the stack and find that you are past
 419      the contents of B67, you have overflowed the segment.
 420
 421      B67 also points to the stack segment linkage control
 422      area, which is what we are really interested in.  */
 423
 424   stkl = CRAY_STACKSEG_END ();
 425   ssptr = (struct stack_segment_linkage *) stkl;
 426
 427   /* If one subtracts 'size' from the end of the segment,
 428      one has the address of the first word of the segment.
 429
 430      If this is not the first segment, 'pseg' will be
 431      nonzero.  */
 432
 433   pseg = ssptr->sspseg;
 434   size = ssptr->sssize;
 435
 436   this_segment = stkl - size;
 437
 438   /* It is possible that calling this routine itself caused
 439      a stack overflow.  Discard stack segments which do not
 440      contain the target address.  */
 441
 442   while (!(this_segment <= address && address <= stkl))
 443     {
 444 #ifdef DEBUG_I00AFUNC
 445       fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
 446 #endif
 447       if (pseg == 0)
 448         break;
 449       stkl = stkl - pseg;
 450       ssptr = (struct stack_segment_linkage *) stkl;
 451       size = ssptr->sssize;
 452       pseg = ssptr->sspseg;
 453       this_segment = stkl - size;
 454     }
 455
 456   result = address - this_segment;
 457
 458   /* If you subtract pseg from the current end of the stack,
 459      you get the address of the previous stack segment's end.
 460      This seems a little convoluted to me, but I'll bet you save
 461      a cycle somewhere.  */
 462
 463   while (pseg != 0)
 464     {
 465 #ifdef DEBUG_I00AFUNC
 466       fprintf (stderr, "%011o %011o\n", pseg, size);
 467 #endif
 468       stkl = stkl - pseg;
 469       ssptr = (struct stack_segment_linkage *) stkl;
 470       size = ssptr->sssize;
 471       pseg = ssptr->sspseg;
 472       result += size;
 473     }
 474   return (result);
 475 }
 476
 477 #endif /* not CRAY2 */
 478 #endif /* CRAY */