linux-kernel - Re: [PATCH v2] compiler.h: Include <linux/bug.h> to avoid build breakage with ARRAY

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Date:	Thu, 1 Mar 2012 21:49:07 -0500
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Fabio Estevam <festevam@...il.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	linux@....linux.org.uk, sam@...nborg.org,
	Fabio Estevam <fabio.estevam@...escale.com>
Subject: Re: [PATCH v2] compiler.h: Include <linux/bug.h> to avoid build
 breakage with ARRAY_SIZE()

On Thu, Mar 1, 2012 at 8:15 PM, Fabio Estevam <festevam@...il.com> 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]))
>
> and BUILD_BUG_ON_ZERO used to be in linux/kernel.h but got moved to
> linux/bug.h.
>
> Hence why people are seeing build breakage with ARRAY_SIZE()."
>
> Signed-off-by: Fabio Estevam <fabio.estevam@...escale.com>

Thanks, but no.

You missed the whole point of my previous comments -- that being
that we don't want to just jam headers into always-used headers.

The compiler.h is going to be an "always used" header.  So if we
can avoid stuffing it full of extra crap, we need to really try.

Paul.

> ---
> Changes since v1:
> - Move linux/bug.h to linux/compiler.h
>
>  include/linux/compiler.h |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 4a24354..0300fb7 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -46,6 +46,7 @@ extern void __chk_io_ptr(const volatile void __iomem *);
>
>  #ifdef __GNUC__
>  #include <linux/compiler-gcc.h>
> +#include <linux/bug.h>
>  #endif
>
>  #define notrace __attribute__((no_instrument_function))
> --
> 1.7.1
>
> --
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