linux-kernel - Re: [PATCH 3/5] jump label: x86 support

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Message-ID: <20100322204048.GD2278@redhat.com>
Date:	Mon, 22 Mar 2010 16:40:48 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	mathieu.desnoyers@...ymtl.ca, hpa@...or.com, tglx@...utronix.de,
	andi@...stfloor.org, roland@...hat.com, rth@...hat.com,
	mhiramat@...hat.com, fweisbec@...il.com
Subject: Re: [PATCH 3/5] jump label: x86 support

On Mon, Mar 22, 2010 at 12:40:25PM -0400, Steven Rostedt wrote:
> > add x86 support for jump label. I'm keeping this patch separate so its clear to
> > arch maintainers what was required for x86 support this new feature. hopefully,
> > it wouldn't be too painful for other arches.
> > 
> > Signed-off-by: Jason Baron <jbaron@...hat.com>
> 
> 
> > +#ifdef __HAVE_ARCH_JUMP_LABEL
> > +
> > +# ifdef CONFIG_X86_64
> > +#  define JUMP_LABEL_NOP P6_NOP5
> > +# else
> > +#  define JUMP_LABEL_NOP ".byte 0xe9 \n\t .long 0\n\t"
> > +# endif
> 
> Are you sure P6_NOP5 can't happen on non 64bit? Just because it is not
> configured does not mean that the CPU can not handle it. Look at the
> code I did in arch/x86/kernel/ftrace.c to determine what nop to use.
> Maybe we can make that generic and have at boot up, the kernel determine
> a proper 5byte nop.
> 

indeed, i've looked at the ftrace nop code...I think was concerned that
I would need a baseline nop that would work for all boxes. But I guess a
jmp + 5 would be it?

-Jason
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