On Mon, Mar 21, 2011 at 2:55 PM, Ian Lance Taylor <iant@google.com> wrote:
> On Sun, Mar 6, 2011 at 9:18 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
>
>> We shouldn't save call frame hard registers as "void *".  This patch
>> changes the unwind library to save call frame hard registers as
>> _Unwind_Word.  OK for 4.7?
>
>> +       PR other/48007
>> +       * unwind-dw2.c (_Unwind_Context): Save call frame hard registers
>> +       as _Unwind_Word.
>> +       (_Unwind_GetGR): Get GR value as _Unwind_Word.
>> +       (_Unwind_SetGR): Set GR value as _Unwind_Word.
>> +       (_Unwind_SetGRValue): Likewise.
>> +       (_Unwind_GetGRPtr): Cast return to "void *".
>> +       (_Unwind_SetGRPtr): Cast pointer to _Unwind_Word.
>> +       (uw_install_context_1): Cast pointer to "void *".
>
> The approach you are using here looks wrong to me.  When looking at
> the DWARF2 _Unwind_Context, you have to look at the by_value field for
> the register.  If by_value is true, then the reg field for that
> register holds an _Unwind_Word which is the value of the register.  If
> by_value is false, then the reg field holds a pointer to the place
> where the actual value is stored.  The size of the actual value is
> determined by dwarf_reg_size_table.  In other words, the reg field is
> a really a union of _Unwind_Word and void*.
>
> You have correctly observed that the current code fails for the case
> where sizeof(_Unwind_Word) > sizeof(void*).  However, the answer is
> not to change the type from void* to _Unwind_Word.  That will fail
> when sizeof(void*) > sizeof(_Unwind_Word).
>
> I think you have to make the reg field a union.
>
> By the way, don't use intptr_t in the unwind code.  Use
> _Unwind_Internal_Ptr.  But I think if you make the field a union, you
> won't need to use either type.
>
> Ian
>
Here is the updated patch. It has

@@ -243,7 +250,7 @@ _Unwind_SetGRPtr (struct _Unwind_Context *context, int index
, void *p)
   index = DWARF_REG_TO_UNWIND_COLUMN (index);
   if (_Unwind_IsExtendedContext (context))
     context->by_value[index] = 0;
-  context->reg[index] = p;
+  context->reg[index].ref = p;
 }

Is that OK to take the address of a union member?


-- 
H.J.
--
2011-03-22  H.J. Lu  <hongjiu.lu@intel.com>

	PR other/48007
	* unwind-dw2.c (_Unwind_Register): New.
	(_Unwind_Context): Save call frame hard registers as
	_Unwind_Register.
	(_Unwind_GetGR): Updated.
	(_Unwind_SetGR): Likewise.
	(_Unwind_SetGRValue): Likewise.
	(_Unwind_GetGRPtr): Likewise.
	(_Unwind_SetGRPtr): Likewise.
	(uw_install_context_1): Likewise.