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

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Date:	Thu, 13 Dec 2012 10:57:07 -0800
From:	Joe Perches <joe@...ches.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	Jiri Kosina <trivial@...nel.org>,
	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" <x86@...nel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"user-mode-linux-devel@...ts.sourceforge.net" 
	<user-mode-linux-devel@...ts.sourceforge.net>,
	"user-mode-linux-user@...ts.sourceforge.net" 
	<user-mode-linux-user@...ts.sourceforge.net>
Subject: Re: [TRIVIAL PATCH 16/26] x86: Convert print_symbol to %pSR

On Thu, 2012-12-13 at 19:37 +0100, Borislav Petkov wrote:
> On Thu, Dec 13, 2012 at 10:23:10AM -0800, Joe Perches wrote:
> > m->ip is a u64 so, when compiling x86-32, there's a new warning
> > "cast to pointer from integer of different size".  This isn't new
> > different behavior, just a new warning.  The previous print_symbol
> > took a ulong and the u64 was silently truncated.
> > 
> >   CC      arch/x86/kernel/cpu/mcheck/mce.o
> > arch/x86/kernel/cpu/mcheck/mce.c: In function ‘print_mce’:
> > arch/x86/kernel/cpu/mcheck/mce.c:246:4: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> > 
> > If appropriate, the code could be changed to
> > 
> > 	(void *)(unsigned long)m->ip
> 
> Can we explicitly cast it to what it is so that we can be explicit as to
> what we're casting it? IOW:
> 
> 	(void *)(__u64)m->ip;
> 
> Does that even work on 32bit?

No, it already is __u64.  You need (unsigned long)
or something else the same size as (void *)

from: arch/x86/include/asm/mce.h

/* Fields are zero when not available */
struct mce {
...
	__u64 ip;

> Also, does the compiler bitch about this useless cast when building with
> W=123?

For x86-32:

With the cast the line is silent.
Without the cast, just the warning about cast.

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