On Mon, Jun 27, 2011 at 7:58 AM, Jason Merrill <jason@redhat.com> wrote:
> On 06/26/2011 05:58 PM, H.J. Lu wrote:
>>
>> The current unwind library scheme provides only one unwind
>> context and is backward compatible with multiple different unwind
>> contexts from multiple unwind libraries:
>>
>> http://gcc.gnu.org/ml/gcc-patches/2006-12/msg01769.html
>>
>> My patch fixes UNITS_PER_WORD > sizeof (void *) and
>> enforces single unwind context when backward compatibility
>> isn't needed.
>
> OK, there seem to be two things going on in this patch:
>
> 1) Handle registers larger than pointers.
> 2) Require that all code share a single copy of the unwinder.
>
> For #2, how are you avoiding the issues Jakub describes in that message?
>  Isn't his scenario 2 still possible?  Are you deciding that it's better to
> abort at run-time in that case?
>
> It seems to me that for targets newer than Jakub's patch we can hard-wire
> _Unwind_IsExtendedContext to true, but making further assumptions would be a
> mistake.
>
> Then, if we're still trying to handle versioning, I think your earlier patch
> for #1 (r170716) that just changes the type of the reg array is a better way
> to go.  But that change should be dependent on a target macro to avoid ABI
> changes for existing targets.
>

This updated patch.  It allows multiple unwind contexts.  It replaces

char by_value[DWARF_FRAME_REGISTERS+1];

with

_Unwind_Word value[DWARF_FRAME_REGISTERS+1];

The code is cleaner than conditionally replacing

void *reg[DWARF_FRAME_REGISTERS+1];

with

_Unwind_Word reg[DWARF_FRAME_REGISTERS+1];

with a bigger unwind context.  But it is more flexible if we
want to extend unwind context later, like saving/restoring
128bit or vector registers which may be bigger than the current
_Unwind_Word.

Thanks.

-- 
H.J.
----
gcc/

2011-06-28  H.J. Lu  <hongjiu.lu@intel.com>

	* config.gcc (libgcc_tm_file): Add i386/value-unwind.h for
	Linux/x86.

	* system.h (REG_VALUE_IN_UNWIND_CONTEXT): Poisoned.

	* unwind-dw2.c (_Unwind_Context): If REG_VALUE_IN_UNWIND_CONTEXT
	is defined, add value and remove by_value.
	(SIGNAL_FRAME_BIT): Define if REG_VALUE_IN_UNWIND_CONTEXT is
	defined.
	(EXTENDED_CONTEXT_BIT): Don't define if REG_VALUE_IN_UNWIND_CONTEXT
	is defined.
	(_Unwind_IsExtendedContext): Likewise.
	(_Unwind_GetGR): Support REG_VALUE_IN_UNWIND_CONTEXT.
	(_Unwind_SetGR): Likewise.
	(_Unwind_GetGRPtr): Likewise.
	(_Unwind_SetGRPtr): Likewise.
	(_Unwind_SetGRValue): Likewise.
	(_Unwind_GRByValue): Likewise.
	(__frame_state_for): Likewise.
	(uw_install_context_1): Likewise.

	* doc/tm.texi.in: Document REG_VALUE_IN_UNWIND_CONTEXT.
	* doc/tm.texi: Regenerated.

libgcc/

2011-06-28  H.J. Lu  <hongjiu.lu@intel.com>

	* config/i386/value-unwind.h: New.