"Fossies" - the Fresh Open Source Software Archive

Member "xemacs-21.4.22/src/alloca.c" (31 Jan 2005, 14856 Bytes) of archive /linux/misc/xemacs-21.4.22.tar.gz:


As a special service "Fossies" has tried to format the requested source page into HTML format using (guessed) C and C++ source code syntax highlighting (style: standard) with prefixed line numbers and code folding option. Alternatively you can here view or download the uninterpreted source code file. For more information about "alloca.c" see the Fossies "Dox" file reference documentation and the last Fossies "Diffs" side-by-side code changes report: 21.4.22_vs_21.5.34.

    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 /* Synched up with: FSF 19.30. */
   25 
   26 /* Authorship:
   27 
   28    FSF: A long time ago.
   29    Very few changes for XEmacs.
   30  */
   31 
   32 #ifdef HAVE_CONFIG_H
   33 #include <config.h>
   34 #endif
   35 
   36 /* XEmacs: If compiling with GCC 2, this file is theoretically not needed.
   37    However, alloca() is broken under GCC 2 on many machines: you
   38    cannot put a call to alloca() as part of an argument to a function.
   39  */
   40 /* If someone has defined alloca as a macro,
   41    there must be some other way alloca is supposed to work.  */
   42 /* XEmacs sometimes uses the C alloca even when a builtin alloca is available,
   43    because it's safer. */
   44 #if defined (EMACS_WANTS_C_ALLOCA) || (!defined (alloca) && (!defined (__GNUC__) || __GNUC__ < 2))
   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 #ifdef __STDC__ /* XEmacs change */
   71 typedef void *pointer;
   72 #else
   73 typedef char *pointer;
   74 #endif
   75 
   76 /* XEmacs: With ERROR_CHECK_MALLOC defined, there is no xfree -- it's
   77    a macro that does some stuff to try and trap invalid frees,
   78    and then calls xfree_1 to actually do the work. */
   79 
   80 #ifdef emacs
   81 # ifdef ERROR_CHECK_MALLOC
   82 void xfree_1 (pointer);
   83 #  define xfree xfree_1
   84 # else
   85 void xfree (pointer);
   86 # endif
   87 #endif
   88 
   89 #ifndef NULL
   90 #define NULL    0
   91 #endif
   92 
   93 /* Different portions of Emacs need to call different versions of
   94    malloc.  The Emacs executable needs alloca to call xmalloc, because
   95    ordinary malloc isn't protected from input signals.  On the other
   96    hand, the utilities in lib-src need alloca to call malloc; some of
   97    them are very simple, and don't have an xmalloc routine.
   98 
   99    Non-Emacs programs expect this to call use xmalloc.
  100 
  101    Callers below should use malloc.  */
  102 
  103 #ifdef emacs
  104 #define malloc xmalloc
  105 #endif
  106 #ifndef WIN32_NATIVE
  107 extern pointer malloc ();
  108 #else
  109 extern void *malloc();
  110 #endif
  111 
  112 /* Define STACK_DIRECTION if you know the direction of stack
  113    growth for your system; otherwise it will be automatically
  114    deduced at run-time.
  115 
  116    STACK_DIRECTION > 0 => grows toward higher addresses
  117    STACK_DIRECTION < 0 => grows toward lower addresses
  118    STACK_DIRECTION = 0 => direction of growth unknown  */
  119 
  120 #ifndef STACK_DIRECTION
  121 #define STACK_DIRECTION 0   /* Direction unknown.  */
  122 #endif
  123 
  124 #if STACK_DIRECTION != 0
  125 
  126 #define STACK_DIR   STACK_DIRECTION /* Known at compile-time.  */
  127 
  128 #else /* STACK_DIRECTION == 0; need run-time code.  */
  129 
  130 static int stack_dir;       /* 1 or -1 once known.  */
  131 #define STACK_DIR   stack_dir
  132 
  133 static void
  134 find_stack_direction ()
  135 {
  136   static char *addr = NULL; /* Address of first `dummy', once known.  */
  137   auto char dummy;      /* To get stack address.  */
  138 
  139   if (addr == NULL)
  140     {               /* Initial entry.  */
  141       addr = ADDRESS_FUNCTION (dummy);
  142 
  143       find_stack_direction ();  /* Recurse once.  */
  144     }
  145   else
  146     {
  147       /* Second entry.  */
  148       if (ADDRESS_FUNCTION (dummy) > addr)
  149     stack_dir = 1;      /* Stack grew upward.  */
  150       else
  151     stack_dir = -1;     /* Stack grew downward.  */
  152     }
  153 }
  154 
  155 #endif /* STACK_DIRECTION == 0 */
  156 
  157 /* An "alloca header" is used to:
  158    (a) chain together all alloca'ed blocks;
  159    (b) keep track of stack depth.
  160 
  161    It is very important that sizeof(header) agree with malloc
  162    alignment chunk size.  The following default should work okay.  */
  163 
  164 #ifndef ALIGN_SIZE
  165 #define ALIGN_SIZE  sizeof(double)
  166 #endif
  167 
  168 typedef union hdr
  169 {
  170   char align[ALIGN_SIZE];   /* To force sizeof(header).  */
  171   struct
  172     {
  173       union hdr *next;      /* For chaining headers.  */
  174       char *deep;       /* For stack depth measure.  */
  175     } h;
  176 } header;
  177 
  178 static header *last_alloca_header = NULL;   /* -> last alloca header.  */
  179 
  180 /* Return a pointer to at least SIZE bytes of storage,
  181    which will be automatically reclaimed upon exit from
  182    the procedure that called alloca.  Originally, this space
  183    was supposed to be taken from the current stack frame of the
  184    caller, but that method cannot be made to work for some
  185    implementations of C, for example under Gould's UTX/32.  */
  186 
  187 pointer
  188 #ifdef EMACS_WANTS_C_ALLOCA
  189 c_alloca (size)
  190 #else
  191 alloca (size)
  192 #endif
  193      unsigned size;
  194 {
  195   auto char probe;      /* Probes stack depth: */
  196   register char *depth = ADDRESS_FUNCTION (probe);
  197 
  198 #if STACK_DIRECTION == 0
  199   if (STACK_DIR == 0)       /* Unknown growth direction.  */
  200     find_stack_direction ();
  201 #endif
  202 
  203   /* Reclaim garbage, defined as all alloca'd storage that
  204      was allocated from deeper in the stack than currently. */
  205 
  206   {
  207     register header *hp;    /* Traverses linked list.  */
  208 
  209     for (hp = last_alloca_header; hp != NULL;)
  210       if ((STACK_DIR > 0 && hp->h.deep > depth)
  211       || (STACK_DIR < 0 && hp->h.deep < depth))
  212     {
  213       register header *np = hp->h.next;
  214 
  215       free ((pointer) hp);  /* Collect garbage.  */
  216 
  217       hp = np;      /* -> next header.  */
  218     }
  219       else
  220     break;          /* Rest are not deeper.  */
  221 
  222     last_alloca_header = hp;    /* -> last valid storage.  */
  223   }
  224 
  225   if (size == 0)
  226     return NULL;        /* No allocation required.  */
  227 
  228   /* Allocate combined header + user data storage.  */
  229 
  230   {
  231     register pointer new = malloc (sizeof (header) + size);
  232     /* Address of header.  */
  233 
  234     ((header *) new)->h.next = last_alloca_header;
  235     ((header *) new)->h.deep = depth;
  236 
  237     last_alloca_header = (header *) new;
  238 
  239     /* User storage begins just after header.  */
  240 
  241     return (pointer) ((char *) new + sizeof (header));
  242   }
  243 }
  244 
  245 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
  246 
  247 #ifdef DEBUG_I00AFUNC
  248 #include <stdio.h>
  249 #endif
  250 
  251 #ifndef CRAY_STACK
  252 #define CRAY_STACK
  253 #ifndef CRAY2
  254 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
  255 struct stack_control_header
  256   {
  257     long shgrow:32;     /* Number of times stack has grown.  */
  258     long shaseg:32;     /* Size of increments to stack.  */
  259     long shhwm:32;      /* High water mark of stack.  */
  260     long shsize:32;     /* Current size of stack (all segments).  */
  261   };
  262 
  263 /* The stack segment linkage control information occurs at
  264    the high-address end of a stack segment.  (The stack
  265    grows from low addresses to high addresses.)  The initial
  266    part of the stack segment linkage control information is
  267    0200 (octal) words.  This provides for register storage
  268    for the routine which overflows the stack.  */
  269 
  270 struct stack_segment_linkage
  271   {
  272     long ss[0200];      /* 0200 overflow words.  */
  273     long sssize:32;     /* Number of words in this segment.  */
  274     long ssbase:32;     /* Offset to stack base.  */
  275     long:32;
  276     long sspseg:32;     /* Offset to linkage control of previous
  277                    segment of stack.  */
  278     long:32;
  279     long sstcpt:32;     /* Pointer to task common address block.  */
  280     long sscsnm;        /* Private control structure number for
  281                    microtasking.  */
  282     long ssusr1;        /* Reserved for user.  */
  283     long ssusr2;        /* Reserved for user.  */
  284     long sstpid;        /* Process ID for pid based multi-tasking.  */
  285     long ssgvup;        /* Pointer to multitasking thread giveup.  */
  286     long sscray[7];     /* Reserved for Cray Research.  */
  287     long ssa0;
  288     long ssa1;
  289     long ssa2;
  290     long ssa3;
  291     long ssa4;
  292     long ssa5;
  293     long ssa6;
  294     long ssa7;
  295     long sss0;
  296     long sss1;
  297     long sss2;
  298     long sss3;
  299     long sss4;
  300     long sss5;
  301     long sss6;
  302     long sss7;
  303   };
  304 
  305 #else /* CRAY2 */
  306 /* The following structure defines the vector of words
  307    returned by the STKSTAT library routine.  */
  308 struct stk_stat
  309   {
  310     long now;           /* Current total stack size.  */
  311     long maxc;          /* Amount of contiguous space which would
  312                    be required to satisfy the maximum
  313                    stack demand to date.  */
  314     long high_water;        /* Stack high-water mark.  */
  315     long overflows;     /* Number of stack overflow ($STKOFEN) calls.  */
  316     long hits;          /* Number of internal buffer hits.  */
  317     long extends;       /* Number of block extensions.  */
  318     long stko_mallocs;      /* Block allocations by $STKOFEN.  */
  319     long underflows;        /* Number of stack underflow calls ($STKRETN).  */
  320     long stko_free;     /* Number of deallocations by $STKRETN.  */
  321     long stkm_free;     /* Number of deallocations by $STKMRET.  */
  322     long segments;      /* Current number of stack segments.  */
  323     long maxs;          /* Maximum number of stack segments so far.  */
  324     long pad_size;      /* Stack pad size.  */
  325     long current_address;   /* Current stack segment address.  */
  326     long current_size;      /* Current stack segment size.  This
  327                    number is actually corrupted by STKSTAT to
  328                    include the fifteen word trailer area.  */
  329     long initial_address;   /* Address of initial segment.  */
  330     long initial_size;      /* Size of initial segment.  */
  331   };
  332 
  333 /* The following structure describes the data structure which trails
  334    any stack segment.  I think that the description in 'asdef' is
  335    out of date.  I only describe the parts that I am sure about.  */
  336 
  337 struct stk_trailer
  338   {
  339     long this_address;      /* Address of this block.  */
  340     long this_size;     /* Size of this block (does not include
  341                    this trailer).  */
  342     long unknown2;
  343     long unknown3;
  344     long link;          /* Address of trailer block of previous
  345                    segment.  */
  346     long unknown5;
  347     long unknown6;
  348     long unknown7;
  349     long unknown8;
  350     long unknown9;
  351     long unknown10;
  352     long unknown11;
  353     long unknown12;
  354     long unknown13;
  355     long unknown14;
  356   };
  357 
  358 #endif /* CRAY2 */
  359 #endif /* not CRAY_STACK */
  360 
  361 #ifdef CRAY2
  362 /* Determine a "stack measure" for an arbitrary ADDRESS.
  363    I doubt that "lint" will like this much. */
  364 
  365 static long
  366 i00afunc (long *address)
  367 {
  368   struct stk_stat status;
  369   struct stk_trailer *trailer;
  370   long *block, size;
  371   long result = 0;
  372 
  373   /* We want to iterate through all of the segments.  The first
  374      step is to get the stack status structure.  We could do this
  375      more quickly and more directly, perhaps, by referencing the
  376      $LM00 common block, but I know that this works.  */
  377 
  378   STKSTAT (&status);
  379 
  380   /* Set up the iteration.  */
  381 
  382   trailer = (struct stk_trailer *) (status.current_address
  383                     + status.current_size
  384                     - 15);
  385 
  386   /* There must be at least one stack segment.  Therefore it is
  387      a fatal error if "trailer" is null.  */
  388 
  389   if (trailer == 0)
  390     ABORT ();
  391 
  392   /* Discard segments that do not contain our argument address.  */
  393 
  394   while (trailer != 0)
  395     {
  396       block = (long *) trailer->this_address;
  397       size = trailer->this_size;
  398       if (block == 0 || size == 0)
  399     ABORT ();
  400       trailer = (struct stk_trailer *) trailer->link;
  401       if ((block <= address) && (address < (block + size)))
  402     break;
  403     }
  404 
  405   /* Set the result to the offset in this segment and add the sizes
  406      of all predecessor segments.  */
  407 
  408   result = address - block;
  409 
  410   if (trailer == 0)
  411     {
  412       return result;
  413     }
  414 
  415   do
  416     {
  417       if (trailer->this_size <= 0)
  418     ABORT ();
  419       result += trailer->this_size;
  420       trailer = (struct stk_trailer *) trailer->link;
  421     }
  422   while (trailer != 0);
  423 
  424   /* We are done.  Note that if you present a bogus address (one
  425      not in any segment), you will get a different number back, formed
  426      from subtracting the address of the first block.  This is probably
  427      not what you want.  */
  428 
  429   return (result);
  430 }
  431 
  432 #else /* not CRAY2 */
  433 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
  434    Determine the number of the cell within the stack,
  435    given the address of the cell.  The purpose of this
  436    routine is to linearize, in some sense, stack addresses
  437    for alloca.  */
  438 
  439 static long
  440 i00afunc (long address)
  441 {
  442   long stkl = 0;
  443 
  444   long size, pseg, this_segment, stack;
  445   long result = 0;
  446 
  447   struct stack_segment_linkage *ssptr;
  448 
  449   /* Register B67 contains the address of the end of the
  450      current stack segment.  If you (as a subprogram) store
  451      your registers on the stack and find that you are past
  452      the contents of B67, you have overflowed the segment.
  453 
  454      B67 also points to the stack segment linkage control
  455      area, which is what we are really interested in.  */
  456 
  457   stkl = CRAY_STACKSEG_END ();
  458   ssptr = (struct stack_segment_linkage *) stkl;
  459 
  460   /* If one subtracts 'size' from the end of the segment,
  461      one has the address of the first word of the segment.
  462 
  463      If this is not the first segment, 'pseg' will be
  464      nonzero.  */
  465 
  466   pseg = ssptr->sspseg;
  467   size = ssptr->sssize;
  468 
  469   this_segment = stkl - size;
  470 
  471   /* It is possible that calling this routine itself caused
  472      a stack overflow.  Discard stack segments which do not
  473      contain the target address.  */
  474 
  475   while (!(this_segment <= address && address <= stkl))
  476     {
  477 #ifdef DEBUG_I00AFUNC
  478       fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
  479 #endif
  480       if (pseg == 0)
  481     break;
  482       stkl = stkl - pseg;
  483       ssptr = (struct stack_segment_linkage *) stkl;
  484       size = ssptr->sssize;
  485       pseg = ssptr->sspseg;
  486       this_segment = stkl - size;
  487     }
  488 
  489   result = address - this_segment;
  490 
  491   /* If you subtract pseg from the current end of the stack,
  492      you get the address of the previous stack segment's end.
  493      This seems a little convoluted to me, but I'll bet you save
  494      a cycle somewhere.  */
  495 
  496   while (pseg != 0)
  497     {
  498 #ifdef DEBUG_I00AFUNC
  499       fprintf (stderr, "%011o %011o\n", pseg, size);
  500 #endif
  501       stkl = stkl - pseg;
  502       ssptr = (struct stack_segment_linkage *) stkl;
  503       size = ssptr->sssize;
  504       pseg = ssptr->sspseg;
  505       result += size;
  506     }
  507   return (result);
  508 }
  509 
  510 #endif /* not CRAY2 */
  511 #endif /* CRAY */
  512 
  513 #endif /* complicated expression at top of file */