Date: Fri, 11 Sep 2009 22:52:28 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "H. Peter Anvin" <hpa@kernel.org>
Cc: Arjan van de Ven <arjan@infradead.org>, Roland McGrath <roland@redhat.com>,
       torvalds@linux-foundation.org, jakub@redhat.com,
       linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
       x86@kernel.org
Subject: Re: [PATCH 1/2] UNREACHABLE() macro
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On Fri, 11 Sep 2009 21:43:42 -0700 "H. Peter Anvin" <hpa@kernel.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@redhat.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.
> 

Use -Wall -Werror and if the compiler doesn't know about
__builtin_unreachable() it will error out.

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