linux-kernel - Re: [PATCH] kexec jump: fix code size checking

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Message-ID: <20080813034857.GA14269@verge.net.au>
Date:	Wed, 13 Aug 2008 13:48:59 +1000
From:	Simon Horman <horms@...ge.net.au>
To:	Huang Ying <ying.huang@...el.com>
Cc:	nigel@...el.suspend2.net,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>, mingo@...e.hu,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH] kexec jump: fix code size checking

On Wed, Aug 13, 2008 at 11:05:15AM +0800, Huang Ying wrote:
> On Wed, 2008-08-13 at 12:47 +1000, Simon Horman wrote:
> > On Wed, Aug 13, 2008 at 09:04:35AM +0800, Huang Ying wrote:
> > > Fix building issue when CONFIG_KEXEC=n. Thanks to Vivek Goyal for his
> > > reminding.
> > > 
> > > Signed-off-by: Huang Ying <ying.huang@...el.com>
> > > 
> > > ---
> > >  include/asm-x86/kexec.h |    3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > --- a/include/asm-x86/kexec.h
> > > +++ b/include/asm-x86/kexec.h
> > > @@ -43,6 +43,9 @@
> > >  
> > >  #ifdef CONFIG_X86_32
> > >  # define KEXEC_CONTROL_CODE_MAX_SIZE	2048
> > > +# ifndef CONFIG_KEXEC
> > > +#  define kexec_control_code_size	0
> > > +# endif
> > >  #endif
> > >  
> > >  #ifndef __ASSEMBLY__
> > 
> > Is it impossible to skip the linker check in the !CONFIG_KEXEC case?
> 
> It is possible. I think there are several ways to do that.
> 
> 1) use #ifdef in vmlinux_32.lds.S, such as:
> 
> #ifdef CONFIG_KEXEC
> ASSERT(kexec_control_code_size <= KEXEC_CONTROL_CODE_MAX_SIZE,
>        "kexec control code size is too big")
> #endif
> 
> 2) #define a macro for kexec check ld script in asm/kexec.h, such as:
> 
> #define LD_CHECK_KEXEC()	ASSERT(kexec_control_code_size <= KEXEC_CONTROL_CODE_MAX_SIZE, \
> 				       "kexec control code size is too big")
> 
> and use that in vmlinux_32.lds.S.
> 
> 3) #define kexec_control_code_size 0. So that the check can be passed
> always. And, code size = 0 is reasonable for no code (CONFIG_KEXEC=n).
> 
> 
> I think 3) is better. What do you think about?

Hi Huang,

I think that 1) with possibly the slight variation of moving
#include <asm/kexec.h> inside #ifdef CONFIG_KEXEC is better
because it avoids introducing kexec_control_code_size,
which is currently only used in arch/x86/kernel/relocate_kernel_32.S
and arch/x86/kernel/vmlinux_32.lds.S, into kexec.h.

/* Link time checks */

#ifdef CONFIG_KEXEC
#include <asm/kexec.h>

ASSERT(kexec_control_code_size <= KEXEC_CONTROL_CODE_MAX_SIZE,
       "kexec control code size is too big")
#endif


My second preference would be 3) as it seems simpler than 2).

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