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