linux-kernel - Re: [PATCH] staging: rts5208: rewrite macro with GNU extension __auto

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Date:   Mon, 04 Nov 2019 09:07:44 -0800
From:   Joe Perches <joe@...ches.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Jules Irenge <jbi.octave@...il.com>
Cc:     outreachy-kernel@...glegroups.com, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: rts5208: rewrite macro with GNU extension
 __auto_type

On Mon, 2019-11-04 at 17:51 +0100, Greg KH wrote:
> On Mon, Nov 04, 2019 at 04:44:00PM +0000, Jules Irenge wrote:
> > Rewrite macro function with GNU extension __auto_type
> > to remove issue detected by checkpatch tool.
> > CHECK: MACRO argument reuse - possible side-effects?
[]
> > diff --git a/drivers/staging/rts5208/rtsx_chip.h b/drivers/staging/rts5208/rtsx_chip.h
[]
> > @@ -386,23 +386,31 @@ struct zone_entry {
> >  
> >  /* SD card */
> >  #define CHK_SD(sd_card)			(((sd_card)->sd_type & 0xFF) == TYPE_SD)
> > -#define CHK_SD_HS(sd_card)		(CHK_SD(sd_card) && \
> > -					 ((sd_card)->sd_type & SD_HS))
[]
> > +#define CHK_SD_HS(sd_card)\
> > +	({__auto_type _sd = sd_card; CHK_SD(_sd) && \
> > +					 (_sd->sd_type & SD_HS); })
[]
> Ick, no.  These are obviously pointers, which can not be "evaluated
> twice" so this whole thing is just fine.
> 
> checkpatch is just a "hint" that you might want to look at the code.
> This stuff is just fine, look at how it is being used for proof of that.

This would also be the first introduction and use of
__auto_type in the kernel.

That's not OK as __auto_type was first supported in
gcc 4.9 and the kernel still compiles with gcc 4.6.