linux-kernel - Re: [PATCH] x86: Use wrmsrl in kprobes.c, step.c

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Date:	Thu, 10 Jan 2008 11:49:02 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Harvey Harrison <harvey.harrison@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Use wrmsrl in kprobes.c, step.c

Harvey Harrison wrote:
> Where x86_32 passed zero in the high 32 bits, use wrmsrl which
> will zero extend for us.  This allows ifdefs for 32/64 bit to
> be eliminated.
> 
> Eliminate ifdef in step.c.  Similar cleanup was done when unifying
> kprobes_32|64.c and wrmsr() was chosen there over wrmsrl().  This
> patch changes these to wrmsrl.
> 
> Signed-off-by: Harvey Harrison <harvey.harrison@...il.com>
> ---
>  arch/x86/kernel/kprobes.c |    4 ++--
>  arch/x86/kernel/step.c    |    4 ----
>  2 files changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
> index 53ba6a5..34becd1 100644
> --- a/arch/x86/kernel/kprobes.c
> +++ b/arch/x86/kernel/kprobes.c
> @@ -410,13 +410,13 @@ static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
>  static void __kprobes clear_btf(void)
>  {
>  	if (test_thread_flag(TIF_DEBUGCTLMSR))
> -		wrmsr(MSR_IA32_DEBUGCTLMSR, 0, 0);
> +		wrmsrl(MSR_IA32_DEBUGCTLMSR, 0L);
>  }

Drop the L.  It doesn't buy you anything, and gcc will sign-extend for 
you anyway.  It's just visual clutter.

	-hpa
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