Re: Dwarf expertise needed

[Sami Wagiaalla <swagiaal@redhat.com>]

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>> That will do, although I think there might be a bug there :(. Let me 
>> double check.
>>     
>
> There is certainly a bug hit by Stan's test case, since it gets an error.
>   
So yes there is a bug, I have not checked to see if it is Stan's bug, 
but here it goes:

This is the test case that I am using:

inline void second(){
  int* a = 0;
  a[0] = 0;          <-------- pc
}

void first(){
  second();
}

int main(){
  first();
  return 0;
}

So if I try to dwarf_getscopes at pc i get 0 scopes returned. The 
problem is in the pc_record function from dwarf_getscopes.c:

>  /* Now we are in a scope that contains the concrete inlined instance.
>     Search it for the inline function's abstract definition.
>     If we don't find it, return to search the containing scope.
>     If we do find it, the nonzero return value will bail us out
>     of the postorder traversal.  */
>  return __libdw_visit_scopes (depth, die, &origin_match, NULL, &a);
> }
The problem is that if the die passed to __libdw_visit_scopes has no 
children, __libdw_visit_scopes returns -1 which means that pc_record 
returns -1 and the search aborts, and no scopes are returned.

The particular childless die in this case happens to be the one 
corresponding to main. I can fudge it by adding some variables to main 
and get the following scopes:

scopes[0] DW_TAG_lexical_block name:
scopes[1] DW_TAG_inlined_subroutine name: second
scopes[2] DW_TAG_compile_unit name: 
/to/scratch/swagiaal/frysks/frysk/frysk-core/frysk/pkglibdir/funit-scopes.c

I have attached two of possible patches:

patch1 just check for children before the call, patch2 takes the 
responsibility away from pc_record and relies on the later call to 
pc_origin in dwarf_getscopes:

[...]
int result = __libdw_visit_scopes (0, &cu, &pc_match, &pc_record, &a);

if (result == 0 && a.scopes != NULL)
  result = __libdw_visit_scopes (0, &cu, &origin_match, NULL, &a);
[...]

I personally like patch2 better. This way you only do two searches.

Thoughts ?

Thanks,
  Sami Wagiaalla

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Index: libdw/dwarf_getscopes.c
===================================================================
RCS file: /cvs/frysk/frysk-imports/elfutils/libdw/dwarf_getscopes.c,v
retrieving revision 1.3
diff -u -r1.3 dwarf_getscopes.c
--- libdw/dwarf_getscopes.c	26 Apr 2007 15:18:42 -0000	1.3
+++ libdw/dwarf_getscopes.c	19 Jul 2007 15:22:53 -0000
@@ -170,6 +170,10 @@
     /* Not there yet.  */
     return 0;
 
+  struct Dwarf_Die_Chain child;
+  if (INTUSE(dwarf_child) (&die->die, &child.die) != 0)
+    return 0;
+
   /* Now we are in a scope that contains the concrete inlined instance.
      Search it for the inline function's abstract definition.
      If we don't find it, return to search the containing scope.

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Index: libdw/dwarf_getscopes.c
===================================================================
RCS file: /cvs/frysk/frysk-imports/elfutils/libdw/dwarf_getscopes.c,v
retrieving revision 1.3
diff -u -r1.3 dwarf_getscopes.c
--- libdw/dwarf_getscopes.c	26 Apr 2007 15:18:42 -0000	1.3
+++ libdw/dwarf_getscopes.c	19 Jul 2007 15:24:47 -0000
@@ -159,23 +159,8 @@
 	return -1;
       return 0;
     }
-
-
-  /* We've recorded the scopes back to one that is a concrete inlined
-     instance.  Now return out of the traversal back to the scope
-     containing that instance.  */
-
-  assert (a->inlined);
-  if (depth >= a->inlined)
-    /* Not there yet.  */
-    return 0;
-
-  /* Now we are in a scope that contains the concrete inlined instance.
-     Search it for the inline function's abstract definition.
-     If we don't find it, return to search the containing scope.
-     If we do find it, the nonzero return value will bail us out
-     of the postorder traversal.  */
-  return __libdw_visit_scopes (depth, die, &origin_match, NULL, &a);
+  
+  return 0;
 }