linux-kernel - Re: [TRIVIAL PATCH 16/26] x86: Convert print

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Date:	Wed, 12 Dec 2012 13:30:03 -0800
From:	Joe Perches <joe@...ches.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Jiri Kosina <trivial@...nel.org>, Tony Luck <tony.luck@...el.com>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net,
	user-mode-linux-user@...ts.sourceforge.net
Subject: Re: [TRIVIAL PATCH 16/26] x86: Convert print_symbol to %pSR

On Wed, 2012-12-12 at 22:09 +0100, Borislav Petkov wrote:
> On Wed, Dec 12, 2012 at 10:19:05AM -0800, Joe Perches wrote:
> > Use the new vsprintf extension to avoid any possible
> > message interleaving.
[]
> > diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
[]
> > @@ -242,13 +242,14 @@ static void print_mce(struct mce *m)
> >  	       m->extcpu, m->mcgstatus, m->bank, m->status);
> >  
> >  	if (m->ip) {
> > -		pr_emerg(HW_ERR "RIP%s %02x:<%016Lx> ",
> > -			!(m->mcgstatus & MCG_STATUS_EIPV) ? " !INEXACT!" : "",
> > -				m->cs, m->ip);
> > -
> >  		if (m->cs == __KERNEL_CS)
> > -			print_symbol("{%s}", m->ip);
> > -		pr_cont("\n");
> > +			pr_emerg(HW_ERR "RIP%s %02x:<%016Lx> {%pSR}\n",
> > +				 !(m->mcgstatus & MCG_STATUS_EIPV) ? " !INEXACT!" : "",
> > +				 m->cs, m->ip, (void *)m->ip);
> > +		else
> > +			pr_emerg(HW_ERR "RIP%s %02x:<%016Lx>\n",
> > +				 !(m->mcgstatus & MCG_STATUS_EIPV) ? " !INEXACT!" : "",
> > +				 m->cs, m->ip);
> >  	}
> 
> I think I'd go ahead and ACK this unless Tony has some comments. I'm not
> happy about the two pr_emerg calls based on the conditional.

It was done to avoid interleaving.

> Or, Tony, what do you think, could we get away if we printed empty
> string for when m->cs != __KERNEL_CS? I'm thinking of not breaking any
> userspace which is parsing that output and seeing "... {}" in that case.
> 
> This assumes that vsprintf can print (void *)0 when passed as an
> argument through %pSR. Joe?

Definitely yes when not #defined CONFIG_KALLSYMS

I believe no object exists at address 0 for all
arches so I believe yes for CONFIG_KALLSYMS too,

My preference is to eventually do away with all the
	"[%0(size)lx] %pSR", addr, (void *)addr
uses and create another %pSx that emits the pointer
address and the function/offset in one go in a
standardized style without caring about the pointer
size.

Something like:

	"%pSp", (void *)addr

would emit

	[<7def0123>] function_name+offset/size


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