linux-kernel - Re: [PATCH 1/2] UNREACHABLE() macro

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Message-ID: <20090912073038.01eecacf@infradead.org>
Date:	Sat, 12 Sep 2009 07:30:38 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	"H. Peter Anvin" <hpa@...nel.org>
Cc:	Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, jakub@...hat.com,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH 1/2] UNREACHABLE() macro

On Fri, 11 Sep 2009 21:43:42 -0700
"H. Peter Anvin" <hpa@...nel.org> wrote:

> On 09/11/2009 08:49 PM, Arjan van de Ven wrote:
> > On Fri, 11 Sep 2009 14:55:25 -0700 (PDT)
> > Roland McGrath <roland@...hat.com> wrote:
> > 
> >>> That's a bit of a mouthful.  Did you consider a runtime probe with
> >>> scripts/Kbuild.include's try-run, cc-option, etc?  
> >>
> >> I did not see any precedent in the sources for using those to test
> >> for features by compiling particular test sources (i.e. in autoconf
> > 
> > look at the stackprotector flags.. they work this way already.
> > It gets done once per kernel build...
> > 
> 
> That works for flags, but not for the presence of builtin functions.
> You can't even just try compiling something, since it will turn into
> an ordinary function if not present... not obvious until link.

"-DGG_HAS_UNREACHABLE" is a compiler flag ;-)
and the shell script can just do a "nm" on the resulting .o file to
detect if it turned into a function call... entirely possible.


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
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