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


On Mon, 18 Aug 2008, Scott Wood wrote:

> Mathieu Desnoyers wrote:
> > asm volatile (
> > "1: lwz %1, 0(%2)\n"
> > " cmpw %1, %5\n"
> > " bne 2f\n"
> > " stwu %3, 0(%2)\n"
> > "2:\n"
> > ".section .fixup, \"ax\"\n"
> > "3: li %0, 1\n"
> > " b 2b\n"
> > ".previous\n"
> > ".section __ex_table,\"a\"\n"
> > _ASM_ALIGN "\n"
> > _ASM_PTR "1b, 3b\n"
> > ".previous"
> > : "=r"(faulted), "=r"(replaced)
> > : "r"(ip), "r"(new),
> > "0"(faulted), "r"(old)
> > : "memory");
>
> Some (most likely unrelated) nits in the above inline asm:

Thanks,

>
> 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 ;-)

> Why stwu with an offset of zero,
> BTW?

Because it worked :-) Really, it has been a while since I did any PPC
assembly, and I didn't break out the old reference manuals to do this.
I simply looked at other asm code, and followed suit. I compiled and
tested it, and it worked. I did make a disclaimer about my rusty PPC
knowledge when I posted the code.

>
> %1 also needs to be an early clobber.

Not exactly sure what you mean by the above.

-- Steve


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