4.3BSD - /usr/src/new/icon/rt/sweep.c

   1: #include "../h/rt.h"
   2: #include "../h/gc.h"
   3: #ifdef VAX
   4: /*
   5:  * sweep - sweep the stack, marking all descriptors there.  Method
   6:  *  is to start at a known point, specifically, the frame that the
   7:  *  fp points to, and then trace back along the stack looking for
   8:  *  descriptors and local variables, marking them when they are found.
   9:  *  The sp starts at the first frame, and then is moved up through
  10:  *  the stack.  Procedure, generator, and expression frames are
  11:  *  recognized when the sp is a certain distance from the fp, gfp,
  12:  *  and efp respectively.
  13:  *
  14:  * Sweeping problems can be manifested in a variety of ways due to
  15:  *  the "if it can't be identified it's a descriptor" methodology.
  16:  */
  17: #undef gfp
  18: #undef efp
  19: #undef fp
  20: sweep(fp)
  21: int *fp;
  22:    {
  23:    register int *sp, *gfp, *efp, *ap;
  24:    int *getap();
  25:    int nargs;
  26: 
  27:    ap = getap(fp);          /* Get pointer to 0(ap) for frame
  28: 					    on top of stack. */
  29:    sp = fp - FRAMELIMIT;        /* Start sp at _file word of current
  30: 					    frame, the lowest word of it. */
  31:    nargs = 0;               /* Nargs counter is 0 initially. */
  32:    while ((fp != 0 || nargs)) {     /* Keep going until current fp is
  33: 					    0 and no arguments are left. */
  34:       if (sp == fp - FRAMELIMIT) {  /* The sp has reached the lower
  35: 					    boundary of a procedure frame,
  36: 					    process the frame. */
  37:          efp = (int *) ap[-1];      /* Get saved efp out of frame, it's
  38: 					    the first word below 0(ap). */
  39:          gfp = (int *) ap[-2];      /* Saved gfp is second word below
  40: 					    0(ap). */
  41:          sp = ap + 2;           /* First argument descriptor is
  42: 					    second word above 0(ap), point
  43: 					    sp at it. */
  44:          ap = (int *) fp[2];        /* Get saved ap */
  45:          fp = (int *) fp[3];        /*  and fp from frame. */
  46:          nargs = sp[-1];        /* Nargs is in word below first
  47: 					    argument descriptor. */
  48:          }
  49:       else if (sp == gfp - 3) {     /* The sp has reached the lower end
  50: 					    of a generator frame, process
  51: 					    the frame.*/
  52:          fp = (int *) gfp[0];       /* Get old fp, available as saved
  53: 					    boundary value in the frame. */
  54:          ap = getap(fp);        /* Find 0(ap) corresponding to just-
  55: 					    restored boundary value. */
  56:          sp = fp - FRAMELIMIT;      /* Set up to trigger recognition of
  57: 					    procedure frame next time around*/
  58:          }
  59:       else if (sp == efp - 2) {     /* The sp has reached the lower end
  60: 					    of a generator frame, process
  61: 					    the frame. */
  62:          gfp = (int *) efp[-1];     /* Restore gfp, */
  63:          efp = (int *) efp[0];      /*  and efp from frame. */
  64:          sp += 3;           /* Move up past expression frame
  65: 					    marker. */
  66:          }
  67:       else {                /* Assume the sp is pointing at a
  68: 					    descriptor. */
  69:          mark(sp);          /* Mark it. */
  70:          sp += 2;           /* Move past descriptor. */
  71:          if (nargs)         /* Decrement argument count if in an*/
  72:             nargs--;            /*  argument list. */
  73:          }
  74:       }
  75:    }
  76: /*
  77:  * getap - return ap of frame addressed by fp
  78:  */
  79: int *getap(fp)
  80: register int *fp;
  81:    {
  82:    register
  83:     int mask = fp[1]>>15 & 0x1ffe;  /* Get register mask out of saved
  84: 					    psw word. */
  85:    fp += 5;             /* Point fp at where first saved
  86: 					    register (if any) is. */
  87:    while (mask >>= 1)           /* Move fp up for each register  */
  88:       fp += mask & 1;           /*  saved.  When done, fp points */
  89:    return fp;               /*  at word where ap would point */
  90:    }
  91: #endif VAX
  92: 
  93: #ifdef PORT
  94: sweep()
  95:    {
  96:    syserr("Call to sweep() in garbage collector not implemented yet");
  97:    }
  98: #endif PORT
  99: 
 100: #ifdef PDP11
 101: /*
 102:  * sweep - sweep the stack, marking all descriptors there.
 103:  */
 104: 
 105: sweep(b)
 106: int *b;
 107:    {
 108:    register int *sp, *r5, *r4;
 109:    int *r3, nargs;
 110: 
 111:    r5 = b;          /* start at last Icon/C boundary */
 112:    sp = r5 - 5;
 113:    nargs = 0;
 114:    while ((r5 != 0 || nargs) && sp < (int *)0177776) {
 115:       if (sp == r5 - 5) {  /* at a procedure frame */
 116:          r3 = r5[-2];
 117:      r4 = r5[-1];
 118:      r5 = r5[0];
 119:      sp += 8;
 120:      nargs = sp[-1];
 121:      }
 122:       else if (sp == r3 - 3) {  /* at a generator frame */
 123:      r5 = r3[0];        /*   go to next boundary */
 124:      sp = r5 - 5;
 125:      }
 126:       else if (sp == r4 - 2) {  /* at an expression frame */
 127:      r3 = r4[-1];
 128:      r4 = r4[0];
 129:      sp += 3;
 130:      }
 131:       else {            /* must be a descriptor! */
 132:      mark(sp);
 133:      sp += 2;
 134:      if (nargs)
 135:         nargs--;
 136:      }
 137:       }
 138:    }
 139: #endif PDP11

Defined functions