linux-kernel - Re: [PATCH v2 5/5] bug: Make BUG() call unreachable()

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Message-Id: <201402261429.06553.arnd@arndb.de>
Date:	Wed, 26 Feb 2014 14:29:06 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] bug: Make BUG() call unreachable()

On Wednesday 26 February 2014, Josh Triplett wrote:
> @@ -134,7 +134,7 @@ extern void warn_slowpath_null(const char *file, const int line);
>  
>  #else /* !CONFIG_BUG */
>  #ifndef HAVE_ARCH_BUG
> -#define BUG() do {} while (0)
> +#define BUG() do { unreachable(); } while (0)
>  #endif

I disagree with this one. As Alan said, we really want to use an
arch specific BUG() even in the !CONFIG_BUG case.

For the cases where this is not yet possible, I'd suggest using

#define BUG() do { } while (1)


For older gcc versions, this is actually the same as unreachable(), but
it is not the same as __builtin_unreachable, because it causes undefined
behavior.

	Arnd
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