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