linux-kernel - Re: [PATCH] um: Adjust current_thread

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Message-ID: <20110422001050.GA468@shutemov.name>
Date:	Fri, 22 Apr 2011 03:10:50 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Richard Weinberger <richard@....at>
Cc:	linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [PATCH] um: Adjust current_thread_info() for gcc-4.6

On Sat, Apr 16, 2011 at 01:03:13AM +0200, Richard Weinberger wrote:
> In some cases gcc-4.6 will optimize away current_thread_info().
> To prevent gcc from doing so the stack address has to be obtained
> via inline asm.
> 
> LKML-Reference: http://marc.info/?i=201104132150.05623.richard@nod.at
> 
> Signed-off-by: Richard Weinberger <richard@....at>

Acked-by: Kirill A. Shutemov <kirill@...temov.name>

Also reproducible with gcc version 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4).

> ---
>  arch/um/include/asm/thread_info.h |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/um/include/asm/thread_info.h b/arch/um/include/asm/thread_info.h
> index e2cf786..5bd1bad 100644
> --- a/arch/um/include/asm/thread_info.h
> +++ b/arch/um/include/asm/thread_info.h
> @@ -49,7 +49,10 @@ static inline struct thread_info *current_thread_info(void)
>  {
>  	struct thread_info *ti;
>  	unsigned long mask = THREAD_SIZE - 1;
> -	ti = (struct thread_info *) (((unsigned long) &ti) & ~mask);
> +	void *p;
> +
> +	asm volatile ("" : "=r" (p) : "0" (&ti));
> +	ti = (struct thread_info *) (((unsigned long)p) & ~mask);
>  	return ti;
>  }
>  
> -- 
> 1.6.6.1
> 
> --
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-- 
 Kirill A. Shutemov
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