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

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Date:	Mon, 18 Aug 2008 12:21:43 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Steven Rostedt <srostedt@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Eran Liberty <liberty@...ricom.com>,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	linuxppc-dev@...abs.org
Subject: Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)

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:

Should use a "b" constraint for %2, or you could get r0.  Or, use an "m" 
constraint with %U2%X2 after the lwz/stw.  Why stwu with an offset of 
zero, BTW?

%1 also needs to be an early clobber.

-Scott
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