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

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Message-ID: <AANLkTimf821jhfhU-Rsj7xa2S4EzuP23weoUSZVWsD2u@mail.gmail.com>
Date:	Tue, 13 Jul 2010 00:52:48 -0700
From:	Chris Li <christ.li@...il.com>
To:	Josh Triplett <josh@...htriplett.org>
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 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.

I will apply the patch until we got better way to handle this.

Chris
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