linux-kernel - Re: any value to "NORET

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Date:	Tue, 22 May 2007 22:34:19 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Adrian Bunk" <bunk@...sta.de>
Cc:	"Robert P. J. Day" <rpjday@...dspring.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: any value to "NORET_TYPE" macro?

On 5/22/07, Adrian Bunk <bunk@...sta.de> wrote:
> On Tue, May 22, 2007 at 10:04:16AM -0400, Robert P. J. Day wrote:
> > On Tue, 22 May 2007, Adrian Bunk wrote:
> >
> > > On Tue, May 22, 2007 at 09:09:22AM -0400, Robert P. J. Day wrote:
> > > >
> > > >   given that:
> > > >
> > > > $ grep -r "define.*NORET_TYPE" *
> > > > include/linux/ext4_fs.h:# define NORET_TYPE    /**/
> > > > include/linux/linkage.h:#define NORET_TYPE    /**/
> > > > include/linux/ext3_fs.h:# define NORET_TYPE    /**/
> > > > $
> > > >
> > > > is there any obvious value to the 30 or so uses of that macro
> > > > sprinkled throughout the tree?
> > >
> > > I can be mistaken, but it seems the uses should be replaced with your
> > > __noreturn
> >
> > no, i think you're thinking of the alternative ATTRIB_NORET macro.
> > as you can read in my previous post, NORET_TYPE used to resolve to
> > "__volatile__" for very old gcc.  so i think it's legitimately dead
> > and can be ripped out.
>
> No doubt that it could be removed because it doesn't have any effect.
>
> But locking at the usages, it seems to have been used when people
> thought it was what __noreturn now is, so replacing NORET_TYPE with
> __noreturn might be a small optimization (but every NORET_TYPE should
> be checked that it's actually correct).

Adrian's right, and in fact from ...

http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html

... we know why that macro existed and evaluated to __volatile__
for pre-2.5 gcc. Perhaps most of today's users of NORET_TYPE were
probably looking for ATTRIB_NORET (which is quite common) actually.

[ __noreturn is defined in compiler-gcc.h, so the easier way would be
to kill NORET_TYPE and replace its usages with ATTRIB_NORET instead.
Of course, after verifying that the function _really_ never returns. ]
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