Initial revision

src/alloca.c

+/* 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 */