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To: tromey@redhat.com
Cc: gdb-patches@sources.redhat.com
Subject: Re: Patch: Dwarf2 reader -vs- DW_OP_piece
References: <87664qej9l.fsf@creche.redhat.com>
	<npr8neqyft.fsf@zwingli.cygnus.com> <87zo22ctbq.fsf@creche.redhat.com>
From: Jim Blandy <jimb@redhat.com>
Date: Sat, 23 Feb 2002 22:15:00 -0000
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That makes sense.

Could you change your patch to detect that pattern, verify that the
register numbers are consecutive (according to DWARF2_REG_TO_REGNUM),
return the number of the first register if everything seems right, and
give a dwarf2_complex_location_expr complaint otherwise?

This is a bit more work, but it's more correct.


Tom Tromey <tromey@redhat.com> writes:

> >>>>> "Jim" == Jim Blandy <jimb@redhat.com> writes:
> 
> Jim> Can you explain what sorts of location expressions this is
> Jim> supposed to help GDB handle?
> 
> Yes, sorry.
> 
> Suppose a value spans multiple registers.  Currently gcc encodes this
> as DW_OP_reg for the first register.  However, I believe that is not
> fully correct according to the Dwarf-2 spec.
> 
> The gcc patch changes the output in this case to a series of
> DW_OP_reg/DW_OP_piece instructions.
> 
> So previously gcc could generate this for a `long long' value (on x86
> Linux):
> 
>     DW_OP_reg1
> 
> With the patch gcc will now generate:
> 
>     DW_OP_reg1
>     DW_OP_piece 4
>     DW_OP_reg2
>     DW_OP_piece 4
> 
> Tom