linux-kernel - Re: [PATCH 2/2] parser: define __builtin

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Message-ID: <20100713181212.GB20289@feather>
Date:	Tue, 13 Jul 2010 11:12:13 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Chris Li <christ.li@...il.com>
Cc:	Jiri Slaby <jslaby@...e.cz>, jirislaby@...il.com,
	Larry Finger <Larry.Finger@...inger.net>,
	linux-kernel@...r.kernel.org, linux-sparse@...r.kernel.org
Subject: Re: [PATCH 2/2] parser: define __builtin_unreachable

On Tue, Jul 13, 2010 at 12:52:48AM -0700, Chris Li wrote:
> On Sat, Jul 10, 2010 at 2:07 AM, Josh Triplett <josh@...htriplett.org> wrote:
> > __builtin_unreachable has special semantics beyond just a function.
> > This definition will suffice to allow compilation, but
> > __builtin_unreachable should have the same effect in sparse that it does
> > in GCC: mark the point (and the remainder of the basic block) as
> > unreachable.  Something like the mechanism used for handling noreturn
> > would work here as well; declaring the function to have attribute
> > noreturn would probably have almost the right semantics.
> >
> 
> The attribute noreturn will apply to the whole function. The function
> NEVER returns.
> __builtin_unreachable only apply to current basic block. e.g. some
> error handling path like panic. The function can still return a value on the
> normal path. It has different meaning than attribute noreturn. So I don't think
> automatically give the function noreturn attribute is the right thing to do.

No, I didn't mean that using __builtin_unreachable should mark the
function calling it as noreturn.  I meant that as an approximation to
the right behavior, __builtin_unreachable *itself* could have attribute
noreturn.

- Josh Triplett
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