Re: [FYI] Inlining support, rough patch

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> From: Tom Tromey <tromey@redhat.com>
> Date: Thu, 18 Jun 2009 11:55:42 -0600
> 
> Ping.
> 
> Mark> I firmly believe that if we want to add the capability to unwind
> Mark> through inlined functions, this fundamental principle should hold for
> Mark> inlined functions as well.  This means that if we can detect that the
> Mark> current register state describes a process executing an inlined
> Mark> function we should faithfully reconstruct the register state for the
> Mark> call site of that inlined function.  If I understand things correctly,
> Mark> the DW_TAG_inlined_subroutine tag provides information about the call
> Mark> site, which gives us the unwound program counter.  But in order to
> Mark> reconstruct the complete register state, we need more information.
> Mark> The only viable source of that information is something like DWARF
> Mark> CFI; you don't stand a chance of doing a proper job here by doing
> Mark> instruction analysis.
> 
> Daniel> DWARF CFI is not going to help with this; it only deals with 'real'
> Daniel> (i.e. not inlined) functions.  There's no saved register state
> Daniel> from the virtual entry point.  There isn't even an indicator
> Daniel> of where inlining occurs.  Are you suggesting enhancing
> Daniel> the CFI information?  I suspect the extra register state
> Daniel> would be generally unretrievable.
> 
> It has been two months since this response.  I think Daniel addressed
> your objections, at least to the extent they are addressable given the
> existing Dwarf specification.
> 
> I would like it if this patch did not stay in limbo any longer.  I
> think that goes for others, too: according to Joel's summit notes,
> this patch was explicitly asked about by attendees.
> 
> At a minimum, could you answer his question above?  Thanks.

Sorry, I have been travelling for the last month.  I still think the
inline unwinder should not bend the rules we established for
unwinders.  But since I'm obviously not capable of coming up with a
better way to do this, please use your own judgements about this diff.