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    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.  */
   40 #if !defined (__GNUC__) || __GNUC__ < 2
   41 
   42 /* If someone has defined alloca as a macro,
   43    there must be some other way alloca is supposed to work.  */
   44 #ifndef alloca
   45 
   46 #ifdef emacs
   47 #ifdef static
   48 /* actually, only want this if static is defined as ""
   49    -- this is for usg, in which emacs must undefine static
   50    in order to make unexec workable
   51    */
   52 #ifndef STACK_DIRECTION
   53 you
   54 lose
   55 -- must know STACK_DIRECTION at compile-time
   56 #endif /* STACK_DIRECTION undefined */
   57 #endif /* static */
   58 #endif /* emacs */
   59 
   60 /* If your stack is a linked list of frames, you have to
   61    provide an "address metric" ADDRESS_FUNCTION macro.  */
   62 
   63 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
   64 long i00afunc ();
   65 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
   66 #else
   67 #define ADDRESS_FUNCTION(arg) &(arg)
   68 #endif
   69 
   70 #if __STDC__
   71 typedef void *pointer;
   72 #else
   73 typedef char *pointer;
   74 #endif
   75 
   76 #ifndef NULL
   77 #define NULL    0
   78 #endif
   79 
   80 /* Different portions of Emacs need to call different versions of
   81    malloc.  The Emacs executable needs alloca to call xmalloc, because
   82    ordinary malloc isn't protected from input signals.  On the other
   83    hand, the utilities in lib-src need alloca to call malloc; some of
   84    them are very simple, and don't have an xmalloc routine.
   85 
   86    Non-Emacs programs expect this to call xmalloc.
   87 
   88    Callers below should use malloc.  */
   89 
   90 #ifndef emacs
   91 #define malloc xmalloc
   92 #endif
   93 extern pointer malloc ();
   94 
   95 /* Define STACK_DIRECTION if you know the direction of stack
   96    growth for your system; otherwise it will be automatically
   97    deduced at run-time.
   98 
   99    STACK_DIRECTION > 0 => grows toward higher addresses
  100    STACK_DIRECTION < 0 => grows toward lower addresses
  101    STACK_DIRECTION = 0 => direction of growth unknown  */
  102 
  103 #ifndef STACK_DIRECTION
  104 #define STACK_DIRECTION 0   /* Direction unknown.  */
  105 #endif
  106 
  107 #if STACK_DIRECTION != 0
  108 
  109 #define STACK_DIR   STACK_DIRECTION /* Known at compile-time.  */
  110 
  111 #else /* STACK_DIRECTION == 0; need run-time code.  */
  112 
  113 static int stack_dir;       /* 1 or -1 once known.  */
  114 #define STACK_DIR   stack_dir
  115 
  116 static void
  117 find_stack_direction ()
  118 {
  119   static char *addr = NULL; /* Address of first `dummy', once known.  */
  120   auto char dummy;      /* To get stack address.  */
  121 
  122   if (addr == NULL)
  123     {               /* Initial entry.  */
  124       addr = ADDRESS_FUNCTION (dummy);
  125 
  126       find_stack_direction ();  /* Recurse once.  */
  127     }
  128   else
  129     {
  130       /* Second entry.  */
  131       if (ADDRESS_FUNCTION (dummy) > addr)
  132     stack_dir = 1;      /* Stack grew upward.  */
  133       else
  134     stack_dir = -1;     /* Stack grew downward.  */
  135     }
  136 }
  137 
  138 #endif /* STACK_DIRECTION == 0 */
  139 
  140 /* An "alloca header" is used to:
  141    (a) chain together all alloca'ed blocks;
  142    (b) keep track of stack depth.
  143 
  144    It is very important that sizeof(header) agree with malloc
  145    alignment chunk size.  The following default should work okay.  */
  146 
  147 #ifndef ALIGN_SIZE
  148 #define ALIGN_SIZE  sizeof(double)
  149 #endif
  150 
  151 typedef union hdr
  152 {
  153   char align[ALIGN_SIZE];   /* To force sizeof(header).  */
  154   struct
  155     {
  156       union hdr *next;      /* For chaining headers.  */
  157       char *deep;       /* For stack depth measure.  */
  158     } h;
  159 } header;
  160 
  161 static header *last_alloca_header = NULL;   /* -> last alloca header.  */
  162 
  163 /* Return a pointer to at least SIZE bytes of storage,
  164    which will be automatically reclaimed upon exit from
  165    the procedure that called alloca.  Originally, this space
  166    was supposed to be taken from the current stack frame of the
  167    caller, but that method cannot be made to work for some
  168    implementations of C, for example under Gould's UTX/32.  */
  169 
  170 pointer
  171 alloca (size)
  172      unsigned size;
  173 {
  174   auto char probe;      /* Probes stack depth: */
  175   register char *depth = ADDRESS_FUNCTION (probe);
  176 
  177 #if STACK_DIRECTION == 0
  178   if (STACK_DIR == 0)       /* Unknown growth direction.  */
  179     find_stack_direction ();
  180 #endif
  181 
  182   /* Reclaim garbage, defined as all alloca'd storage that
  183      was allocated from deeper in the stack than currently.  */
  184 
  185   {
  186     register header *hp;    /* Traverses linked list.  */
  187 
  188 #ifdef emacs
  189     BLOCK_INPUT;
  190 #endif
  191 
  192     for (hp = last_alloca_header; hp != NULL;)
  193       if ((STACK_DIR > 0 && hp->h.deep > depth)
  194       || (STACK_DIR < 0 && hp->h.deep < depth))
  195     {
  196       register header *np = hp->h.next;
  197 
  198       free ((pointer) hp);  /* Collect garbage.  */
  199 
  200       hp = np;      /* -> next header.  */
  201     }
  202       else
  203     break;          /* Rest are not deeper.  */
  204 
  205     last_alloca_header = hp;    /* -> last valid storage.  */
  206 
  207 #ifdef emacs
  208     UNBLOCK_INPUT;
  209 #endif
  210   }
  211 
  212   if (size == 0)
  213     return NULL;        /* No allocation required.  */
  214 
  215   /* Allocate combined header + user data storage.  */
  216 
  217   {
  218     register pointer new = malloc (sizeof (header) + size);
  219     /* Address of header.  */
  220 
  221     if (new == 0)
  222       abort();
  223 
  224     ((header *) new)->h.next = last_alloca_header;
  225     ((header *) new)->h.deep = depth;
  226 
  227     last_alloca_header = (header *) new;
  228 
  229     /* User storage begins just after header.  */
  230 
  231     return (pointer) ((char *) new + sizeof (header));
  232   }
  233 }
  234 
  235 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
  236 
  237 #ifdef DEBUG_I00AFUNC
  238 #include <stdio.h>
  239 #endif
  240 
  241 #ifndef CRAY_STACK
  242 #define CRAY_STACK
  243 #ifndef CRAY2
  244 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
  245 struct stack_control_header
  246   {
  247     long shgrow:32;     /* Number of times stack has grown.  */
  248     long shaseg:32;     /* Size of increments to stack.  */
  249     long shhwm:32;      /* High water mark of stack.  */
  250     long shsize:32;     /* Current size of stack (all segments).  */
  251   };
  252 
  253 /* The stack segment linkage control information occurs at
  254    the high-address end of a stack segment.  (The stack
  255    grows from low addresses to high addresses.)  The initial
  256    part of the stack segment linkage control information is
  257    0200 (octal) words.  This provides for register storage
  258    for the routine which overflows the stack.  */
  259 
  260 struct stack_segment_linkage
  261   {
  262     long ss[0200];      /* 0200 overflow words.  */
  263     long sssize:32;     /* Number of words in this segment.  */
  264     long ssbase:32;     /* Offset to stack base.  */
  265     long:32;
  266     long sspseg:32;     /* Offset to linkage control of previous
  267                    segment of stack.  */
  268     long:32;
  269     long sstcpt:32;     /* Pointer to task common address block.  */
  270     long sscsnm;        /* Private control structure number for
  271                    microtasking.  */
  272     long ssusr1;        /* Reserved for user.  */
  273     long ssusr2;        /* Reserved for user.  */
  274     long sstpid;        /* Process ID for pid based multi-tasking.  */
  275     long ssgvup;        /* Pointer to multitasking thread giveup.  */
  276     long sscray[7];     /* Reserved for Cray Research.  */
  277     long ssa0;
  278     long ssa1;
  279     long ssa2;
  280     long ssa3;
  281     long ssa4;
  282     long ssa5;
  283     long ssa6;
  284     long ssa7;
  285     long sss0;
  286     long sss1;
  287     long sss2;
  288     long sss3;
  289     long sss4;
  290     long sss5;
  291     long sss6;
  292     long sss7;
  293   };
  294 
  295 #else /* CRAY2 */
  296 /* The following structure defines the vector of words
  297    returned by the STKSTAT library routine.  */
  298 struct stk_stat
  299   {
  300     long now;           /* Current total stack size.  */
  301     long maxc;          /* Amount of contiguous space which would
  302                    be required to satisfy the maximum
  303                    stack demand to date.  */
  304     long high_water;        /* Stack high-water mark.  */
  305     long overflows;     /* Number of stack overflow ($STKOFEN) calls.  */
  306     long hits;          /* Number of internal buffer hits.  */
  307     long extends;       /* Number of block extensions.  */
  308     long stko_mallocs;      /* Block allocations by $STKOFEN.  */
  309     long underflows;        /* Number of stack underflow calls ($STKRETN).  */
  310     long stko_free;     /* Number of deallocations by $STKRETN.  */
  311     long stkm_free;     /* Number of deallocations by $STKMRET.  */
  312     long segments;      /* Current number of stack segments.  */
  313     long maxs;          /* Maximum number of stack segments so far.  */
  314     long pad_size;      /* Stack pad size.  */
  315     long current_address;   /* Current stack segment address.  */
  316     long current_size;      /* Current stack segment size.  This
  317                    number is actually corrupted by STKSTAT to
  318                    include the fifteen word trailer area.  */
  319     long initial_address;   /* Address of initial segment.  */
  320     long initial_size;      /* Size of initial segment.  */
  321   };
  322 
  323 /* The following structure describes the data structure which trails
  324    any stack segment.  I think that the description in 'asdef' is
  325    out of date.  I only describe the parts that I am sure about.  */
  326 
  327 struct stk_trailer
  328   {
  329     long this_address;      /* Address of this block.  */
  330     long this_size;     /* Size of this block (does not include
  331                    this trailer).  */
  332     long unknown2;
  333     long unknown3;
  334     long link;          /* Address of trailer block of previous
  335                    segment.  */
  336     long unknown5;
  337     long unknown6;
  338     long unknown7;
  339     long unknown8;
  340     long unknown9;
  341     long unknown10;
  342     long unknown11;
  343     long unknown12;
  344     long unknown13;
  345     long unknown14;
  346   };
  347 
  348 #endif /* CRAY2 */
  349 #endif /* not CRAY_STACK */
  350 
  351 #ifdef CRAY2
  352 /* Determine a "stack measure" for an arbitrary ADDRESS.
  353    I doubt that "lint" will like this much.  */
  354 
  355 static long
  356 i00afunc (long *address)
  357 {
  358   struct stk_stat status;
  359   struct stk_trailer *trailer;
  360   long *block, size;
  361   long result = 0;
  362 
  363   /* We want to iterate through all of the segments.  The first
  364      step is to get the stack status structure.  We could do this
  365      more quickly and more directly, perhaps, by referencing the
  366      $LM00 common block, but I know that this works.  */
  367 
  368   STKSTAT (&status);
  369 
  370   /* Set up the iteration.  */
  371 
  372   trailer = (struct stk_trailer *) (status.current_address
  373                     + status.current_size
  374                     - 15);
  375 
  376   /* There must be at least one stack segment.  Therefore it is
  377      a fatal error if "trailer" is null.  */
  378 
  379   if (trailer == 0)
  380     #ifdef BAF_MODULE
  381 wget_abort(__FUNCTION__,__FILE__,__LINE__);
  382 #else
  383 abort();
  384 #endif
  385 
  386   /* Discard segments that do not contain our argument address.  */
  387 
  388   while (trailer != 0)
  389     {
  390       block = (long *) trailer->this_address;
  391       size = trailer->this_size;
  392       if (block == 0 || size == 0)
  393     #ifdef BAF_MODULE
  394 wget_abort(__FUNCTION__,__FILE__,__LINE__);
  395 #else
  396 abort();
  397 #endif
  398       trailer = (struct stk_trailer *) trailer->link;
  399       if ((block <= address) && (address < (block + size)))
  400     break;
  401     }
  402 
  403   /* Set the result to the offset in this segment and add the sizes
  404      of all predecessor segments.  */
  405 
  406   result = address - block;
  407 
  408   if (trailer == 0)
  409     {
  410       return result;
  411     }
  412 
  413   do
  414     {
  415       if (trailer->this_size <= 0)
  416     #ifdef BAF_MODULE
  417 wget_abort(__FUNCTION__,__FILE__,__LINE__);
  418 #else
  419 abort();
  420 #endif
  421       result += trailer->this_size;
  422       trailer = (struct stk_trailer *) trailer->link;
  423     }
  424   while (trailer != 0);
  425 
  426   /* We are done.  Note that if you present a bogus address (one
  427      not in any segment), you will get a different number back, formed
  428      from subtracting the address of the first block.  This is probably
  429      not what you want.  */
  430 
  431   return (result);
  432 }
  433 
  434 #else /* not CRAY2 */
  435 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
  436    Determine the number of the cell within the stack,
  437    given the address of the cell.  The purpose of this
  438    routine is to linearize, in some sense, stack addresses
  439    for alloca.  */
  440 
  441 static long
  442 i00afunc (long address)
  443 {
  444   long stkl = 0;
  445 
  446   long size, pseg, this_segment, stack;
  447   long result = 0;
  448 
  449   struct stack_segment_linkage *ssptr;
  450 
  451   /* Register B67 contains the address of the end of the
  452      current stack segment.  If you (as a subprogram) store
  453      your registers on the stack and find that you are past
  454      the contents of B67, you have overflowed the segment.
  455 
  456      B67 also points to the stack segment linkage control
  457      area, which is what we are really interested in.  */
  458 
  459   stkl = CRAY_STACKSEG_END ();
  460   ssptr = (struct stack_segment_linkage *) stkl;
  461 
  462   /* If one subtracts 'size' from the end of the segment,
  463      one has the address of the first word of the segment.
  464 
  465      If this is not the first segment, 'pseg' will be
  466      nonzero.  */
  467 
  468   pseg = ssptr->sspseg;
  469   size = ssptr->sssize;
  470 
  471   this_segment = stkl - size;
  472 
  473   /* It is possible that calling this routine itself caused
  474      a stack overflow.  Discard stack segments which do not
  475      contain the target address.  */
  476 
  477   while (!(this_segment <= address && address <= stkl))
  478     {
  479 #ifdef DEBUG_I00AFUNC
  480       fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
  481 #endif
  482       if (pseg == 0)
  483     break;
  484       stkl = stkl - pseg;
  485       ssptr = (struct stack_segment_linkage *) stkl;
  486       size = ssptr->sssize;
  487       pseg = ssptr->sspseg;
  488       this_segment = stkl - size;
  489     }
  490 
  491   result = address - this_segment;
  492 
  493   /* If you subtract pseg from the current end of the stack,
  494      you get the address of the previous stack segment's end.
  495      This seems a little convoluted to me, but I'll bet you save
  496      a cycle somewhere.  */
  497 
  498   while (pseg != 0)
  499     {
  500 #ifdef DEBUG_I00AFUNC
  501       fprintf (stderr, "%011o %011o\n", pseg, size);
  502 #endif
  503       stkl = stkl - pseg;
  504       ssptr = (struct stack_segment_linkage *) stkl;
  505       size = ssptr->sssize;
  506       pseg = ssptr->sspseg;
  507       result += size;
  508     }
  509   return (result);
  510 }
  511 
  512 #endif /* not CRAY2 */
  513 #endif /* CRAY */
  514 
  515 #endif /* no alloca */
  516 #endif /* not GCC version 2 */