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From: Chris Li <christ.li@gmail.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Jiri Slaby <jslaby@suse.cz>,
	jirislaby@gmail.com, Larry Finger <Larry.Finger@lwfinger.net>,
	linux-kernel@vger.kernel.org, linux-sparse@vger.kernel.org
Subject: Re: [PATCH 2/2] parser: define __builtin_unreachable
Date: Tue, 13 Jul 2010 00:52:48 -0700	[thread overview]
Message-ID: <AANLkTimf821jhfhU-Rsj7xa2S4EzuP23weoUSZVWsD2u@mail.gmail.com> (raw)
In-Reply-To: <20100710090705.GA14881@feather>

On Sat, Jul 10, 2010 at 2:07 AM, Josh Triplett <josh@joshtriplett.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

WARNING: multiple messages have this Message-ID (diff)
From: Chris Li <christ.li@gmail.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Jiri Slaby <jslaby@suse.cz>,
	jirislaby@gmail.com, Larry Finger <Larry.Finger@lwfinger.net>,
	linux-kernel@vger.kernel.org, linux-sparse@vger.kernel.org
Subject: Re: [PATCH 2/2] parser: define __builtin_unreachable
Date: Tue, 13 Jul 2010 00:52:48 -0700	[thread overview]
Message-ID: <AANLkTimf821jhfhU-Rsj7xa2S4EzuP23weoUSZVWsD2u@mail.gmail.com> (raw)
In-Reply-To: <20100710090705.GA14881@feather>

On Sat, Jul 10, 2010 at 2:07 AM, Josh Triplett <josh@joshtriplett.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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  reply	other threads:[~2010-07-13  7:52 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-07-09  1:52 Warning message when using sparse Larry Finger
2010-07-09 20:47 ` Jiri Slaby
2010-07-09 21:22   ` Larry Finger
2010-07-09 21:26     ` Jiri Slaby
2010-07-09 22:04       ` Christopher Li
2010-07-10  8:39         ` [PATCH 1/2] parser: fix and simplify support of asm goto Jiri Slaby
2010-07-10 18:36           ` Chris Li
2010-07-10 18:36             ` Chris Li
2010-07-10  8:39         ` [PATCH 2/2] parser: define __builtin_unreachable Jiri Slaby
2010-07-10  9:07           ` Josh Triplett
2010-07-13  7:52             ` Chris Li [this message]
2010-07-13  7:52               ` Chris Li
2010-07-13 18:12               ` Josh Triplett
2010-07-13 18:49                 ` Chris Li
2010-07-13 18:49                   ` Chris Li

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