linux-kernel - Re: [PATCH v4 4/4] asm-generic: fix build error in fix_to_virt with CONFIG_CC_OPTIMIZE_FOR

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Date:   Wed, 9 May 2018 08:52:24 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     changbin.du@...el.com
Cc:     yamada.masahiro@...ionext.com, michal.lkml@...kovi.net,
        tglx@...utronix.de, mingo@...hat.com, akpm@...ux-foundation.org,
        rdunlap@...radead.org, x86@...nel.org, lgirdwood@...il.com,
        broonie@...nel.org, arnd@...db.de, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH v4 4/4] asm-generic: fix build error in fix_to_virt with
 CONFIG_CC_OPTIMIZE_FOR_DEBUGGING

On Wed,  9 May 2018 16:43:16 +0800
changbin.du@...el.com wrote:

> From: Changbin Du <changbin.du@...el.com>
> 
> With '-Og' optimization level, GCC would not optimize a count for a loop
> as a constant value. But BUILD_BUG_ON() only accept compile-time constant
> values. Let's use __fix_to_virt() to avoid the error.
> 
> arch/arm/mm/mmu.o: In function `fix_to_virt':
> /home/changbin/work/linux/./include/asm-generic/fixmap.h:31: undefined reference to `__compiletime_assert_31'
> Makefile:1051: recipe for target 'vmlinux' failed
> make: *** [vmlinux] Error 1

Perhaps we should put this patch ahead of patch 3. Why allow it to
break?

Anyway, besides that, I think the series looks good.

For the series: Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve


> 
> Signed-off-by: Changbin Du <changbin.du@...el.com>
> 
> ---
> v2: use __fix_to_virt() to fix the issue.
> ---
>  arch/arm/mm/mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index e46a6a4..c08d74e 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -1599,7 +1599,7 @@ static void __init early_fixmap_shutdown(void)
>  		pte_t *pte;
>  		struct map_desc map;
>  
> -		map.virtual = fix_to_virt(i);
> +		map.virtual = __fix_to_virt(i);
>  		pte = pte_offset_early_fixmap(pmd_off_k(map.virtual), map.virtual);
>  
>  		/* Only i/o device mappings are supported ATM */