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Re: [Libunwind-devel] libunwind x86-64 optimisations?

From: Daniel Jacobowitz
Subject: Re: [Libunwind-devel] libunwind x86-64 optimisations?
Date: Mon, 6 Jul 2009 12:39:34 -0400
User-agent: Mutt/1.5.20 (2009-06-14)

On Mon, Jul 06, 2009 at 06:20:55PM +0200, Lassi Tuura wrote:
> >This could also be a dynamic stack realignment (for support of
> >vectorization).  I didn't think x86-64 needed that, though.
> OK, in the libraries I looked there's basically only use of r{6,7}
> +/- offset as a CFA. There's tons of DW_CFA_def_cfa_offset{,_sf} use
> which I meant the CFA isn't just a simple register value but an
> expression. (There were exceptions for syscalls and longjmp, but I
> think I can live with those :-)

That's just register+offset.  You have to handle an offset; it's
pretty much never at offset 0.

You have to count on there being a few exceptions, but if they only
make you run the slower unwinder, it doesn't matter.  This will cover
the majority.

Daniel Jacobowitz

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