From: David Howells <dhowells@redhat.com>
To: David Daney <ddaney.cavm@gmail.com>
Cc: dhowells@redhat.com, ralf@linux-mips.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Rientjes <rientjes@google.com>, DM <dm.n9107@gmail.com>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
David Daney <david.daney@cavium.com>
Subject: Re: [PATCH v2 1/2] kernel.h: Add BUILD_BUG() macro.
Date: Wed, 23 Nov 2011 11:11:20 +0000 [thread overview]
Message-ID: <2657.1322046680@redhat.com> (raw)
In-Reply-To: <1321985686-798-2-git-send-email-ddaney.cavm@gmail.com>
David Daney <ddaney.cavm@gmail.com> wrote:
> From: David Daney <david.daney@cavium.com>
>
> We can place this in definitions that we expect the compiler to remove
> by dead code elimination. If this assertion fails, we get a nice
> error message at build time.
>
> The GCC function attribute error("message") was added in version 4.3,
> so we define a new macro __linktime_error(message) to expand to this
> for GCC-4.3 and later. This will give us an error diagnostic from the
> compiler on the line that fails. For other compilers
> __linktime_error(message) expands to nothing, and we have to be
> content with a link time error, but at least we will still get a build
> error.
>
> BUILD_BUG() expands to the undefined function __build_bug_failed() and
> will fail at link time if the compiler ever emits code for it. On
> GCC-4.3 and later, attribute((error())) is used so that the failure
> will be noted at compile time instead.
>
> Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: David Howells <dhowells@redhat.com>
next prev parent reply other threads:[~2011-11-23 11:11 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-22 18:14 [PATCH v2 0/2] Stop some of the abuse of BUG() where compile time checks should be used David Daney
2011-11-22 18:14 ` David Daney
2011-11-22 18:14 ` [PATCH v2 1/2] kernel.h: Add BUILD_BUG() macro David Daney
2011-11-23 1:34 ` David Rientjes
2011-11-23 11:11 ` David Howells [this message]
2011-11-22 18:14 ` [PATCH v2 2/2] hugetlb: Replace BUG() with BUILD_BUG() for dummy definitions David Daney
2011-11-23 1:35 ` David Rientjes
2011-11-23 11:11 ` David Howells
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