linux-kernel - Re: [PATCH] thinkpad_acpi: Remove side effects from vdbg_printk -> no

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Date:	Thu, 27 Aug 2015 14:32:15 -0300
From:	Henrique de Moraes Holschuh <hmh@....eng.br>
To:	Joe Perches <joe@...ches.com>
Cc:	Darren Hart <dvhart@...radead.org>,
	ibm-acpi-devel@...ts.sourceforge.net,
	platform-driver-x86@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thinkpad_acpi: Remove side effects from vdbg_printk ->
 no_printk macro

On Wed, 26 Aug 2015, Joe Perches wrote:
> On Wed, 2015-08-26 at 15:27 -0300, Henrique de Moraes Holschuh wrote:
> > On Wed, Aug 26, 2015, at 15:13, Joe Perches wrote:
> > > vdbg_printk when not using CONFIG_THINKPAD_ACPI_DEBUG uses
> > > no_printk which produces no logging output but always
> > > evaluates arguments.
> > > 
> > > Change the macro to surround the no_printk call with
> > > 	do { if (0) no_printk(...); } while (0)
> > > to avoid the unnecessary argument evaluations.
> > > 
> > > $ size drivers/platform/x86/thinkpad_acpi.o*
> > >    text       data     bss     dec     hex filename
> > >   60918      6184     824   67926   10956
> > >   drivers/platform/x86/thinkpad_acpi.o.new
> > >   60927      6184     824   67935   1095f
> > >   drivers/platform/x86/thinkpad_acpi.o.old
> > 
> > The code size savings of this change are really small...
> 
> yup.  This is just an on-the-way patch to get
> all the no_printk uses in a state that can
> be converted more simply to a side-effect free
> mechanism.
> 
> > > --- a/drivers/platform/x86/thinkpad_acpi.c
> > > +++ b/drivers/platform/x86/thinkpad_acpi.c
> > > @@ -402,7 +402,7 @@ static const char *str_supported(int is_supported);
> > >  #else
> > >  static inline const char *str_supported(int is_supported) { return ""; }
> > >  #define vdbg_printk(a_dbg_level, format, arg...)        \
> > > -       no_printk(format, ##arg)
> > > +       do { if (0) no_printk(format, ##arg); } while (0)
> > >  #endif
> > 
> > And won't this change disable compile-time checking of 'format ## arg'
> > for issues?
> 
> No.  The call is still there so the compiler checks
> the format/argument matches, but eliminates the
> call and any side-effect calls from the object file.

Ok, very well.  In that case, I will ack it.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh
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