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Message-ID: <1488673507.2870.109.camel@kernel.crashing.org>
Subject: Re: [PATCH] powerpc: Avoid panic during boot due to divide by zero
 in init_cache_info()
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Anton Blanchard <anton@ozlabs.org>, paulus@samba.org, mpe@ellerman.id.au
Cc: linuxppc-dev@lists.ozlabs.org
Date: Sun, 05 Mar 2017 11:25:07 +1100
In-Reply-To: <1488671674-20833-1-git-send-email-anton@ozlabs.org>
References: <1488671674-20833-1-git-send-email-anton@ozlabs.org>
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On Sun, 2017-03-05 at 10:54 +1100, Anton Blanchard wrote:
> From: Anton Blanchard <anton@samba.org>
> 
> I see a panic in early boot when building with a recent gcc
> toolchain.
> The issue is a divide by zero, which is undefined. Older toolchains
> let us get away with it:

Maybe we should panic though ... not having a valid cache block size is
going to be fatal in other areas...

> int foo(int a) { return a / 0; }
> 
> foo:
> 	li 9,0
> 	divw 3,3,9
> 	extsw 3,3
> 	blr
> 
> But newer ones catch it:
> 
> foo:
> 	trap
> 
> Add a check to avoid the divide by zero.
> 
> Fixes: bd067f83b084 ("powerpc/64: Fix naming of cache block vs. cache
> line")
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
>  arch/powerpc/kernel/setup_64.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/setup_64.c
> b/arch/powerpc/kernel/setup_64.c
> index adf2084..afd1c26 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -408,7 +408,8 @@ static void init_cache_info(struct ppc_cache_info
> *info, u32 size, u32 lsize,
>  	info->line_size = lsize;
>  	info->block_size = bsize;
>  	info->log_block_size = __ilog2(bsize);
> -	info->blocks_per_page = PAGE_SIZE / bsize;
> +	if (bsize)
> +		info->blocks_per_page = PAGE_SIZE / bsize;
>  
>  	if (sets == 0)
>  		info->assoc = 0xffff;