+/* alloca.c -- allocate automatically reclaimed memory
+ (Mostly) portable public-domain implementation -- D A Gwyn
+
+ This implementation of the PWB library alloca function,
+ which is used to allocate space off the run-time stack so
+ that it is automatically reclaimed upon procedure exit,
+ was inspired by discussions with J. Q. Johnson of Cornell.
+ J.Otto Tennant <jot@cray.com> contributed the Cray support.
+
+ There are some preprocessor constants that can
+ be defined when compiling for your specific system, for
+ improved efficiency; however, the defaults should be okay.
+
+ The general concept of this implementation is to keep
+ track of all alloca-allocated blocks, and reclaim any
+ that are found to be deeper in the stack than the current
+ invocation. This heuristic does not reclaim storage as
+ soon as it becomes invalid, but it will do so eventually.
+
+ As a special case, alloca(0) reclaims storage without
+ allocating any. It is a good idea to use alloca(0) in
+ your main control loop, etc. to force garbage collection. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+/* If compiling with GCC, this file's not needed. */
+#ifndef alloca
+
+#ifdef emacs
+#ifdef static
+/* actually, only want this if static is defined as ""
+ -- this is for usg, in which emacs must undefine static
+ in order to make unexec workable
+ */
+#ifndef STACK_DIRECTION
+you
+lose
+-- must know STACK_DIRECTION at compile-time
+#endif /* STACK_DIRECTION undefined */
+#endif /* static */
+#endif /* emacs */
+
+#ifdef emacs
+#define free xfree
+#endif
+
+/* If your stack is a linked list of frames, you have to
+ provide an "address metric" ADDRESS_FUNCTION macro. */
+
+#ifdef CRAY
+long i00afunc ();
+#define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
+#else
+#define ADDRESS_FUNCTION(arg) &(arg)
+#endif
+
+#if __STDC__
+typedef void *pointer;
+#else
+typedef char *pointer;
+#endif
+
+#define NULL 0
+
+extern pointer xmalloc ();
+
+/* Define STACK_DIRECTION if you know the direction of stack
+ growth for your system; otherwise it will be automatically
+ deduced at run-time.
+
+ STACK_DIRECTION > 0 => grows toward higher addresses
+ STACK_DIRECTION < 0 => grows toward lower addresses
+ STACK_DIRECTION = 0 => direction of growth unknown */
+
+#ifndef STACK_DIRECTION
+#define STACK_DIRECTION 0 /* Direction unknown. */
+#endif
+
+#if STACK_DIRECTION != 0
+
+#define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
+
+#else /* STACK_DIRECTION == 0; need run-time code. */
+
+static int stack_dir; /* 1 or -1 once known. */
+#define STACK_DIR stack_dir
+
+static void
+find_stack_direction ()
+{
+ static char *addr = NULL; /* Address of first `dummy', once known. */
+ auto char dummy; /* To get stack address. */
+
+ if (addr == NULL)
+ { /* Initial entry. */
+ addr = ADDRESS_FUNCTION (dummy);
+
+ find_stack_direction (); /* Recurse once. */
+ }
+ else
+ {
+ /* Second entry. */
+ if (ADDRESS_FUNCTION (dummy) > addr)
+ stack_dir = 1; /* Stack grew upward. */
+ else
+ stack_dir = -1; /* Stack grew downward. */
+ }
+}
+
+#endif /* STACK_DIRECTION == 0 */
+
+/* An "alloca header" is used to:
+ (a) chain together all alloca'ed blocks;
+ (b) keep track of stack depth.
+
+ It is very important that sizeof(header) agree with malloc
+ alignment chunk size. The following default should work okay. */
+
+#ifndef ALIGN_SIZE
+#define ALIGN_SIZE sizeof(double)
+#endif
+
+typedef union hdr
+{
+ char align[ALIGN_SIZE]; /* To force sizeof(header). */
+ struct
+ {
+ union hdr *next; /* For chaining headers. */
+ char *deep; /* For stack depth measure. */
+ } h;
+} header;
+
+static header *last_alloca_header = NULL; /* -> last alloca header. */
+
+/* Return a pointer to at least SIZE bytes of storage,
+ which will be automatically reclaimed upon exit from
+ the procedure that called alloca. Originally, this space
+ was supposed to be taken from the current stack frame of the
+ caller, but that method cannot be made to work for some
+ implementations of C, for example under Gould's UTX/32. */
+
+pointer
+alloca (size)
+ unsigned size;
+{
+ auto char probe; /* Probes stack depth: */
+ register char *depth = ADDRESS_FUNCTION (probe);
+
+#if STACK_DIRECTION == 0
+ if (STACK_DIR == 0) /* Unknown growth direction. */
+ find_stack_direction ();
+#endif
+
+ /* Reclaim garbage, defined as all alloca'd storage that
+ was allocated from deeper in the stack than currently. */
+
+ {
+ register header *hp; /* Traverses linked list. */
+
+ for (hp = last_alloca_header; hp != NULL;)
+ if ((STACK_DIR > 0 && hp->h.deep > depth)
+ || (STACK_DIR < 0 && hp->h.deep < depth))
+ {
+ register header *np = hp->h.next;
+
+ free ((pointer) hp); /* Collect garbage. */
+
+ hp = np; /* -> next header. */
+ }
+ else
+ break; /* Rest are not deeper. */
+
+ last_alloca_header = hp; /* -> last valid storage. */
+ }
+
+ if (size == 0)
+ return NULL; /* No allocation required. */
+
+ /* Allocate combined header + user data storage. */
+
+ {
+ register pointer new = xmalloc (sizeof (header) + size);
+ /* Address of header. */
+
+ ((header *) new)->h.next = last_alloca_header;
+ ((header *) new)->h.deep = depth;
+
+ last_alloca_header = (header *) new;
+
+ /* User storage begins just after header. */
+
+ return (pointer) ((char *) new + sizeof (header));
+ }
+}
+
+#ifdef CRAY
+
+#ifdef DEBUG_I00AFUNC
+#include <stdio.h>
+#endif
+
+#ifndef CRAY_STACK
+#define CRAY_STACK
+#ifndef CRAY2
+/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
+struct stack_control_header
+ {
+ long shgrow:32; /* Number of times stack has grown. */
+ long shaseg:32; /* Size of increments to stack. */
+ long shhwm:32; /* High water mark of stack. */
+ long shsize:32; /* Current size of stack (all segments). */
+ };
+
+/* The stack segment linkage control information occurs at
+ the high-address end of a stack segment. (The stack
+ grows from low addresses to high addresses.) The initial
+ part of the stack segment linkage control information is
+ 0200 (octal) words. This provides for register storage
+ for the routine which overflows the stack. */
+
+struct stack_segment_linkage
+ {
+ long ss[0200]; /* 0200 overflow words. */
+ long sssize:32; /* Number of words in this segment. */
+ long ssbase:32; /* Offset to stack base. */
+ long:32;
+ long sspseg:32; /* Offset to linkage control of previous
+ segment of stack. */
+ long:32;
+ long sstcpt:32; /* Pointer to task common address block. */
+ long sscsnm; /* Private control structure number for
+ microtasking. */
+ long ssusr1; /* Reserved for user. */
+ long ssusr2; /* Reserved for user. */
+ long sstpid; /* Process ID for pid based multi-tasking. */
+ long ssgvup; /* Pointer to multitasking thread giveup. */
+ long sscray[7]; /* Reserved for Cray Research. */
+ long ssa0;
+ long ssa1;
+ long ssa2;
+ long ssa3;
+ long ssa4;
+ long ssa5;
+ long ssa6;
+ long ssa7;
+ long sss0;
+ long sss1;
+ long sss2;
+ long sss3;
+ long sss4;
+ long sss5;
+ long sss6;
+ long sss7;
+ };
+
+#else /* CRAY2 */
+/* The following structure defines the vector of words
+ returned by the STKSTAT library routine. */
+struct stk_stat
+ {
+ long now; /* Current total stack size. */
+ long maxc; /* Amount of contiguous space which would
+ be required to satisfy the maximum
+ stack demand to date. */
+ long high_water; /* Stack high-water mark. */
+ long overflows; /* Number of stack overflow ($STKOFEN) calls. */
+ long hits; /* Number of internal buffer hits. */
+ long extends; /* Number of block extensions. */
+ long stko_mallocs; /* Block allocations by $STKOFEN. */
+ long underflows; /* Number of stack underflow calls ($STKRETN). */
+ long stko_free; /* Number of deallocations by $STKRETN. */
+ long stkm_free; /* Number of deallocations by $STKMRET. */
+ long segments; /* Current number of stack segments. */
+ long maxs; /* Maximum number of stack segments so far. */
+ long pad_size; /* Stack pad size. */
+ long current_address; /* Current stack segment address. */
+ long current_size; /* Current stack segment size. This
+ number is actually corrupted by STKSTAT to
+ include the fifteen word trailer area. */
+ long initial_address; /* Address of initial segment. */
+ long initial_size; /* Size of initial segment. */
+ };
+
+/* The following structure describes the data structure which trails
+ any stack segment. I think that the description in 'asdef' is
+ out of date. I only describe the parts that I am sure about. */
+
+struct stk_trailer
+ {
+ long this_address; /* Address of this block. */
+ long this_size; /* Size of this block (does not include
+ this trailer). */
+ long unknown2;
+ long unknown3;
+ long link; /* Address of trailer block of previous
+ segment. */
+ long unknown5;
+ long unknown6;
+ long unknown7;
+ long unknown8;
+ long unknown9;
+ long unknown10;
+ long unknown11;
+ long unknown12;
+ long unknown13;
+ long unknown14;
+ };
+
+#endif /* CRAY2 */
+#endif /* not CRAY_STACK */
+
+#ifdef CRAY2
+/* Determine a "stack measure" for an arbitrary ADDRESS.
+ I doubt that "lint" will like this much. */
+
+static long
+i00afunc (long *address)
+{
+ struct stk_stat status;
+ struct stk_trailer *trailer;
+ long *block, size;
+ long result = 0;
+
+ /* We want to iterate through all of the segments. The first
+ step is to get the stack status structure. We could do this
+ more quickly and more directly, perhaps, by referencing the
+ $LM00 common block, but I know that this works. */
+
+ STKSTAT (&status);
+
+ /* Set up the iteration. */
+
+ trailer = (struct stk_trailer *) (status.current_address
+ + status.current_size
+ - 15);
+
+ /* There must be at least one stack segment. Therefore it is
+ a fatal error if "trailer" is null. */
+
+ if (trailer == 0)
+ abort ();
+
+ /* Discard segments that do not contain our argument address. */
+
+ while (trailer != 0)
+ {
+ block = (long *) trailer->this_address;
+ size = trailer->this_size;
+ if (block == 0 || size == 0)
+ abort ();
+ trailer = (struct stk_trailer *) trailer->link;
+ if ((block <= address) && (address < (block + size)))
+ break;
+ }
+
+ /* Set the result to the offset in this segment and add the sizes
+ of all predecessor segments. */
+
+ result = address - block;
+
+ if (trailer == 0)
+ {
+ return result;
+ }
+
+ do
+ {
+ if (trailer->this_size <= 0)
+ abort ();
+ result += trailer->this_size;
+ trailer = (struct stk_trailer *) trailer->link;
+ }
+ while (trailer != 0);
+
+ /* We are done. Note that if you present a bogus address (one
+ not in any segment), you will get a different number back, formed
+ from subtracting the address of the first block. This is probably
+ not what you want. */
+
+ return (result);
+}
+
+#else /* not CRAY2 */
+/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
+ Determine the number of the cell within the stack,
+ given the address of the cell. The purpose of this
+ routine is to linearize, in some sense, stack addresses
+ for alloca. */
+
+static long
+i00afunc (long address)
+{
+ long stkl = 0;
+
+ long size, pseg, this_segment, stack;
+ long result = 0;
+
+ struct stack_segment_linkage *ssptr;
+
+ /* Register B67 contains the address of the end of the
+ current stack segment. If you (as a subprogram) store
+ your registers on the stack and find that you are past
+ the contents of B67, you have overflowed the segment.
+
+ B67 also points to the stack segment linkage control
+ area, which is what we are really interested in. */
+
+ stkl = CRAY_STACKSEG_END ();
+ ssptr = (struct stack_segment_linkage *) stkl;
+
+ /* If one subtracts 'size' from the end of the segment,
+ one has the address of the first word of the segment.
+
+ If this is not the first segment, 'pseg' will be
+ nonzero. */
+
+ pseg = ssptr->sspseg;
+ size = ssptr->sssize;
+
+ this_segment = stkl - size;
+
+ /* It is possible that calling this routine itself caused
+ a stack overflow. Discard stack segments which do not
+ contain the target address. */
+
+ while (!(this_segment <= address && address <= stkl))
+ {
+#ifdef DEBUG_I00AFUNC
+ fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
+#endif
+ if (pseg == 0)
+ break;
+ stkl = stkl - pseg;
+ ssptr = (struct stack_segment_linkage *) stkl;
+ size = ssptr->sssize;
+ pseg = ssptr->sspseg;
+ this_segment = stkl - size;
+ }
+
+ result = address - this_segment;
+
+ /* If you subtract pseg from the current end of the stack,
+ you get the address of the previous stack segment's end.
+ This seems a little convoluted to me, but I'll bet you save
+ a cycle somewhere. */
+
+ while (pseg != 0)
+ {
+#ifdef DEBUG_I00AFUNC
+ fprintf (stderr, "%011o %011o\n", pseg, size);
+#endif
+ stkl = stkl - pseg;
+ ssptr = (struct stack_segment_linkage *) stkl;
+ size = ssptr->sssize;
+ pseg = ssptr->sspseg;
+ result += size;
+ }
+ return (result);
+}
+
+#endif /* not CRAY2 */
+#endif /* CRAY */
+
+#endif /* no alloca */
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