linux-kernel - Re: [PATCH] kernel.h: Include <linux/bug.h> to avoid build breakage with ARRAY

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Message-ID: <20120228155124.GA2827@merkur.ravnborg.org>
Date:	Tue, 28 Feb 2012 16:51:24 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Fabio Estevam <fabio.estevam@...escale.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	paul.gortmaker@...driver.com, linux@....linux.org.uk
Subject: Re: [PATCH] kernel.h: Include <linux/bug.h> to avoid build
	breakage with ARRAY_SIZE()

On Tue, Feb 28, 2012 at 10:41:39AM -0300, Fabio Estevam wrote:
> Building imx_v6_v7_defconfig generated the following build error:
> 
> arch/arm/mach-imx/cpu_op-mx51.c: In function 'mx51_get_cpu_op':
> arch/arm/mach-imx/cpu_op-mx51.c:27: error: implicit declaration of function 'BUILD_BUG_ON_ZERO'
> 
> commit 6f863554 (kernel.h: doesn't explicitly use bug.h, so don't include it.)
> has removed asm/debug.h from linux/kernel.h.
> 
> Quoting Russell King (http://www.spinics.net/lists/arm-kernel/msg161916.html)
> 
> "linux/kernel.h _does_ use bug stuff - in ARRAY_SIZE().
> 
> ARRAY_SIZE() uses __must_be_array(), which is defined in linux/compiler-gcc.h,
> which is obtained via linux/compiler.h and linux/linkage.h.
> 
> linux/compiler-gcc.h defines __must_be_array() to be:
> #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))

In which case linux/compiler-gcc.h uses bug.h - so this is where you
should add the include.
Not in kernel.h that just happens to use __must_be_array()
We do not want to add "#include bug.h" to all header files
that happens to use __must_be_array.

	Sam
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