linux-kernel - Re: [PATCH] x86: Use v8086_mode helper, trivial unification

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Message-Id: <1200622862.5724.106.camel@brick>
Date:	Thu, 17 Jan 2008 18:21:02 -0800
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Roland McGrath <roland@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86: Use v8086_mode helper, trivial unification

On Thu, 2008-01-17 at 20:36 -0500, H. Peter Anvin wrote:
> Roland McGrath wrote:
> > It's indeed true that &pt_regs is truly the esp value for x86-32
> > kernel-mode trap frames.  Because this nonobvious calculation is 
> > only right for a kernel mode pt_regs and not for a user-mode one,
> > I think it would be better to use a name for the inline/macro that
> > makes this quite clear, rather than one so generic as "stack_addr".
> 
> Indeed.  This was certainly highly nonobvious in the current code.
> 

What do you think of:

/*
 * (unsigned long)regs looks strange, but it's correct for x86_32.  x86_32 CPUs
 * don't save the ss and esp registers if the CPU is already in kernel mode
 * when it traps.  So &regs happens to be esp.  Valid only for kernel-mode
 * pt_regs.
 */
static inline unsigned long stack_pointer(struct pt_regs *regs)
{
#ifdef CONFIG_X86_32
	return (unsigned long)regs;
#else
	return regs->sp;
#endif
}

Harvey

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