linux-kernel - Re: [PATCH -tip] x86: acpi/sleep.c saved

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Date:	Fri, 10 Apr 2009 21:29:39 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jaswinder Singh Rajput <jaswinder@...nel.org>
Cc:	Pavel Machek <pavel@....cz>, Ingo Molnar <mingo@...e.hu>,
	x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, josh@...edesktop.org
Subject: Re: [PATCH -tip] x86: acpi/sleep.c saved_magic fix overflow

On Sat, Apr 11, 2009 at 12:46:56AM +0530, Jaswinder Singh Rajput wrote:
> On Fri, 2009-04-10 at 21:13 +0200, Sam Ravnborg wrote:
> > On Fri, Apr 10, 2009 at 07:55:45PM +0200, Pavel Machek wrote:
> > > On Fri 2009-04-10 23:06:55, Jaswinder Singh Rajput wrote:
> > > > Impact: fix overflow
> > > 
> > > > Constant 0x123456789abcdef0 is so big for a long.
> > > > So using saved_magic 0x12345678 for both 32 and 64 bit.
> > > 
> > > Have you tested the patch? I have feeling that this is tested from
> > > assembly... Plus it is only set to long constant on 64-bit, so I don't
> > > think you are fixing anything. And if your code is correct the
> > > variable is write only...
> > 
> > $ git grep saved_magic
> > kernel/acpi/sleep.c:    saved_magic = 0x12345678;
> > kernel/acpi/sleep.c:    saved_magic = 0x123456789abcdef0;
> > kernel/acpi/sleep.h:extern long saved_magic;
> > kernel/acpi/wakeup_32.S:        movl    %cs:saved_magic, %eax
> > kernel/acpi/wakeup_32.S:ENTRY(saved_magic)      .long   0
> > kernel/acpi/wakeup_64.S:        movq    saved_magic, %rax
> > kernel/acpi/wakeup_64.S:ENTRY(saved_magic)      .quad   0
> > 
> > 
> > wakeup_32.S:
> >         movl    %cs:saved_magic, %eax
> >         cmpl    $0x12345678, %eax
> > 
> > wakeup_64.S:
> >         movq    saved_magic, %rax
> >         movq    $0x123456789abcdef0, %rdx
> > 
> > So patch is obviously bogus.
> > 
> 
> Sorry, I was confused by this sparse warning on 64 bit box:
> 
> CHECK   arch/x86/kernel/acpi/sleep.c
>  arch/x86/kernel/acpi/sleep.c:107:16: warning: constant 0x123456789abcdef0 is so big it is long
> 
> atleast I found problem in sparse ;-)

Sparse tells you that the constant is so big it is long - correct.
So rather than being implicit appending an L would make sparse happy.

So please use the constant 0x123456789abcdef0L and I think sparse is silenced.
And code/functionality is the same.

	Sam
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