Re: Can't make a stack from a continuation

Marius Vollmer <marius.vollmer@xxxxxxxxxxxxxxx> writes:

> Neil Jerram <neil@xxxxxxxxxxxxxxxxx> writes:
>
>> And one more problem ... the same problem exists in CVS head, but a
>> similar patch doesn't fix it ... still investigating.
>
> I'm looking into this as well, now.  The fix you did for 1.6 looks
> good, although I don't understand it completely yet.  I will try to
> come up with my own patch to CVS head.

Here it is.  I have already applied it to CVS.  I think a similar
scheme can be used for 1.6, too: i.e., move the offset calculation
into scm_make_continuation.

Neil, do you want to fix 1.6 yourself?

Index: continuations.c
===================================================================
RCS file: /cvsroot/guile/guile/guile-core/libguile/continuations.c,v
retrieving revision 1.54
diff -u -r1.54 continuations.c
--- continuations.c     22 Oct 2004 15:13:12 -0000      1.54
+++ continuations.c     23 Dec 2004 15:26:20 -0000
@@ -134,6 +134,7 @@
 #if ! SCM_STACK_GROWS_UP
   src -= stack_size;
 #endif
+  continuation->offset = continuation->stack - src;
   memcpy (continuation->stack, src, sizeof (SCM_STACKITEM) * stack_size);
 
 #ifdef __ia64__
Index: continuations.h
===================================================================
RCS file: /cvsroot/guile/guile/guile-core/libguile/continuations.h,v
retrieving revision 1.31
diff -u -r1.31 continuations.h
--- continuations.h     25 Jun 2003 18:12:35 -0000      1.31
+++ continuations.h     23 Dec 2004 15:26:20 -0000
@@ -55,8 +55,19 @@
   size_t num_stack_items;   /* size of the saved stack.  */
   unsigned long seq;        /* dynamic root identifier.  */
 
-  /* the most recently created debug frame on the live stack, before
-     it was saved.  */
+  /* The offset from the live stack location and this copy.  This is
+     used to adjust pointers from within the copied stack to the stack
+     itself.
+
+     Thus, when you read a pointer from the copied stack that points
+     into the live stack, you need to add OFFSET so that it points
+     into the copy.
+  */
+  scm_t_ptrdiff offset;
+
+  /* The most recently created debug frame on the live stack, before
+     it was saved.  This need to be adjusted with OFFSET, above.
+  */
   struct scm_t_debug_frame *dframe;
 
   SCM_STACKITEM stack[1];    /* copied stack of size num_stack_items.  */ 
Index: stacks.c
===================================================================
RCS file: /cvsroot/guile/guile/guile-core/libguile/stacks.c,v
retrieving revision 1.80
diff -u -r1.80 stacks.c
--- stacks.c    22 Sep 2004 17:41:37 -0000      1.80
+++ stacks.c    23 Dec 2004 15:26:20 -0000
@@ -124,7 +124,8 @@
  * is read from a continuation.
  */
 static scm_t_bits
-stack_depth (scm_t_debug_frame *dframe, long offset, SCM *id, int *maxp)
+stack_depth (scm_t_debug_frame *dframe, scm_t_ptrdiff offset,
+            SCM *id, int *maxp)
 {
   long n;
   long max_depth = SCM_BACKTRACE_MAXDEPTH;
@@ -134,11 +135,12 @@
     {
       if (SCM_EVALFRAMEP (*dframe))
        {
-         scm_t_debug_info * info = RELOC_INFO (dframe->info, offset);
-         n += (info - dframe->vect) / 2 + 1;
+         scm_t_debug_info *info = RELOC_INFO (dframe->info, offset);
+         scm_t_debug_info *vect = RELOC_INFO (dframe->vect, offset);
+         n += (info - vect) / 2 + 1;
          /* Data in the apply part of an eval info frame comes from previous
             stack frame if the scm_t_debug_info vector is overflowed. */
-         if ((((info - dframe->vect) & 1) == 0)
+         if ((((info - vect) & 1) == 0)
              && SCM_OVERFLOWP (*dframe)
              && !SCM_UNBNDP (info[1].a.proc))
            ++n;
@@ -147,7 +149,7 @@
        ++n;
     }
   if (dframe && SCM_VOIDFRAMEP (*dframe))
-    *id = dframe->vect[0].id;
+    *id = RELOC_INFO(dframe->vect, offset)[0].id;
   else if (dframe)
     *maxp = 1;
   return n;
@@ -156,13 +158,15 @@
 /* Read debug info from DFRAME into IFRAME.
  */
 static void
-read_frame (scm_t_debug_frame *dframe, long offset, scm_t_info_frame *iframe)
+read_frame (scm_t_debug_frame *dframe, scm_t_ptrdiff offset,
+           scm_t_info_frame *iframe)
 {
   scm_t_bits flags = SCM_UNPACK (SCM_INUM0); /* UGh. */
   if (SCM_EVALFRAMEP (*dframe))
     {
-      scm_t_debug_info * info = RELOC_INFO (dframe->info, offset);
-      if ((info - dframe->vect) & 1)
+      scm_t_debug_info *info = RELOC_INFO (dframe->info, offset);
+      scm_t_debug_info *vect = RELOC_INFO (dframe->vect, offset);
+      if ((info - vect) & 1)
        {
          /* Debug.vect ends with apply info. */
          --info;
@@ -179,9 +183,10 @@
     }
   else
     {
+      scm_t_debug_info *vect = RELOC_INFO (dframe->vect, offset);
       flags |= SCM_FRAMEF_PROC;
-      iframe->proc = dframe->vect[0].a.proc;
-      iframe->args = dframe->vect[0].a.args;
+      iframe->proc = vect[0].a.proc;
+      iframe->args = vect[0].a.args;
     }
   iframe->flags = flags;
 }
@@ -223,10 +228,11 @@
  */
 
 static scm_t_bits
-read_frames (scm_t_debug_frame *dframe, long offset, long n, scm_t_info_frame 
*iframes)
+read_frames (scm_t_debug_frame *dframe, scm_t_ptrdiff offset,
+            long n, scm_t_info_frame *iframes)
 {
   scm_t_info_frame *iframe = iframes;
-  scm_t_debug_info *info;
+  scm_t_debug_info *info, *vect;
   static SCM applybody = SCM_UNDEFINED;
   
   /* The value of applybody has to be setup after r4rs.scm has executed. */
@@ -248,7 +254,8 @@
              --iframe;
            }
          info =  RELOC_INFO (dframe->info, offset);
-         if ((info - dframe->vect) & 1)
+         vect =  RELOC_INFO (dframe->vect, offset);
+         if ((info - vect) & 1)
            --info;
          /* Data in the apply part of an eval info frame comes from
             previous stack frame if the scm_t_debug_info vector is
@@ -265,7 +272,7 @@
            iframe->flags |= SCM_FRAMEF_OVERFLOW;
          info -= 2;
          NEXT_FRAME (iframe, n, quit);
-         while (info >= dframe->vect)
+         while (info >= vect)
            {
              if (!SCM_UNBNDP (info[1].a.proc))
                {
@@ -435,12 +442,9 @@
     }
   else if (SCM_CONTINUATIONP (obj))
     {
-      offset = ((SCM_STACKITEM *) ((char *) SCM_CONTREGS (obj) + sizeof 
(scm_t_contregs))
-               - SCM_BASE (obj));
-#if SCM_STACK_GROWS_UP
-      offset += SCM_CONTINUATION_LENGTH (obj);
-#endif
-      dframe = RELOC_FRAME (SCM_DFRAME (obj), offset);
+      scm_t_contregs *cont = SCM_CONTREGS (obj);
+      offset = cont->offset;
+      dframe = RELOC_FRAME (cont->dframe, offset);
     }
   else
     {
@@ -463,7 +467,7 @@
   SCM_STACK (stack) -> frames = iframe;
 
   /* Translate the current chain of stack frames into debugging information. */
-  n = read_frames (RELOC_FRAME (dframe, offset), offset, n, iframe);
+  n = read_frames (dframe, offset, n, iframe);
   SCM_STACK (stack) -> length = n;
 
   /* Narrow the stack according to the arguments given to scm_make_stack. */
@@ -519,12 +523,9 @@
     }
   else if (SCM_CONTINUATIONP (stack))
     {
-      offset = ((SCM_STACKITEM *) ((char *) SCM_CONTREGS (stack) + sizeof 
(scm_t_contregs))
-               - SCM_BASE (stack));
-#if SCM_STACK_GROWS_UP
-      offset += SCM_CONTINUATION_LENGTH (stack);
-#endif
-      dframe = RELOC_FRAME (SCM_DFRAME (stack), offset);
+      scm_t_contregs *cont = SCM_CONTREGS (stack);
+      offset = cont->offset;
+      dframe = RELOC_FRAME (cont->dframe, offset);
     }
   else if (SCM_STACKP (stack))
     {
@@ -538,7 +539,7 @@
   while (dframe && !SCM_VOIDFRAMEP (*dframe))
     dframe = RELOC_FRAME (dframe->prev, offset);
   if (dframe && SCM_VOIDFRAMEP (*dframe))
-    return dframe->vect[0].id;
+    return RELOC_INFO (dframe->vect, offset)[0].id;
   return SCM_BOOL_F;
 }
 #undef FUNC_NAME
@@ -595,12 +596,9 @@
     }
   else if (SCM_CONTINUATIONP (obj))
     {
-      offset = ((SCM_STACKITEM *) ((char *) SCM_CONTREGS (obj) + sizeof 
(scm_t_contregs))
-               - SCM_BASE (obj));
-#if SCM_STACK_GROWS_UP
-      offset += SCM_CONTINUATION_LENGTH (obj);
-#endif
-      dframe = RELOC_FRAME (SCM_DFRAME (obj), offset);
+      scm_t_contregs *cont = SCM_CONTREGS (obj);
+      offset = cont->offset;
+      dframe = RELOC_FRAME (cont->dframe, offset);
     }
   else
     {


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