linux-kernel - Re: [PATCH 1/4] Make vsyscall_gtod

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Date:	Thu, 30 Jan 2014 11:51:49 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	andriy.shevchenko@...ux.intel.com, Martin.Runge@...de-schwarz.com,
	Andreas.Brief@...de-schwarz.com
Subject: Re: [PATCH 1/4] Make vsyscall_gtod_data handling x86 generic

On Thu, Jan 30, 2014 at 11:27 AM, Stefani Seibold <stefani@...bold.net> wrote:
> Am Donnerstag, den 30.01.2014, 10:05 -0800 schrieb Andy Lutomirski:
>> On Thu, Jan 30, 2014 at 2:49 AM,  <stefani@...bold.net> wrote:
>> > diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
>> > index 59c6c40..45ba688 100644
>> > --- a/arch/x86/include/asm/compat.h
>> > +++ b/arch/x86/include/asm/compat.h
>> > @@ -295,6 +295,10 @@ static inline compat_uptr_t ptr_to_compat(void __user *uptr)
>> >
>> >  static inline void __user *arch_compat_alloc_user_space(long len)
>> >  {
>> > +#ifdef CONFIG_X86_32
>> > +       struct pt_regs *regs = task_pt_regs(current);
>> > +       return (void __user *)regs->sp - len;
>>
>> Is there some reason this doesn't need to be aligned?
>>
>
> The reason is that this function will not used for 32 bit kernels, but
> will the header will be included... This prevents an error!

Then why not just guard the whole function with an ifdef?  Having a
piece of actual code that's not intended to be used (and might not
work) seems like a bad idea.

--Andy
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