Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)

[Scott Wood]

Steven Rostedt wrote:
> > Should use a "b" constraint for %2, or you could get r0. 
>
> I will make an updated patch.
>
> > Or, use an "m"
> > constraint with %U2%X2 after the lwz/stw. 
>
> The 'b' seems easier ;-)

The advantage of the latter is that it allows GCC to choose indexed or 
update instructions -- but that's merely an optimization.  Switching to 
"b" is enough to avoid the potential bug.

> > %1 also needs to be an early clobber.
>
> Not exactly sure what you mean by the above.

%1 is written to before some inputs are consumed, so you need to use 
"=&r" rather than "=r" so that GCC won't use the same register for both.

-Scott
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