Subject: Re: PowerPC ftrace function trace optimisation

From: Alan Modra <[email-masked]>
Date: Thu, 29 Apr 2010 10:52:52 +0930

On Thu, Apr 29, 2010 at 11:02:47AM +1000, Benjamin Herrenschmidt wrote:
> From a quick test it appears that this only works with -m64, not -m32.
> Alan is that correct ?

Yes.

> Any chance you can fix that in future gcc versions ?

No need really.  32-bit _mcount calls happen before the prologue
anyway.

> > In fact if we are careful when switching to the new mcount ABI and don't
> > rely on the store of r0, we could probably optimise this even further in a
> > future gcc and remove the store completely. mcount would be 2 instructions:
> > 
> >    mflr    r0              
> >    bl      8 <.foo+0x8>

Yeah.  Also, I should have used a different name for this mcount from
the standard 64-bit mcount.

-- 
Alan Modra
Australia Development Lab, IBM