linux-kernel - Re: [PATCH bpf-next] xsk: fix 64-bit division

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Date:   Mon, 7 May 2018 11:25:24 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Björn Töpel <bjorn.topel@...il.com>,
        ast@...com, daniel@...earbox.net, netdev@...r.kernel.org
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        magnus.karlsson@...el.com, linux-next@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next] xsk: fix 64-bit division

On 05/07/2018 10:43 AM, Björn Töpel wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
> 
> i386 builds report:
>   net/xdp/xdp_umem.o: In function `xdp_umem_reg':
>   xdp_umem.c:(.text+0x47e): undefined reference to `__udivdi3'
> 
> This fix uses div_u64 instead of the GCC built-in.
> 
> Fixes: c0c77d8fb787 ("xsk: add user memory registration support sockopt")
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>

I don't know why the subject says xsk (instead of xdp), but anyway:

Reported-by: Randy Dunlap <rdunlap@...radead.org>
Tested-by: Randy Dunlap <rdunlap@...radead.org>

Thanks.

> ---
>  net/xdp/xdp_umem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> index 881dfdefe235..2b47a1dd7c6c 100644
> --- a/net/xdp/xdp_umem.c
> +++ b/net/xdp/xdp_umem.c
> @@ -209,7 +209,7 @@ int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
>  	if ((addr + size) < addr)
>  		return -EINVAL;
>  
> -	nframes = size / frame_size;
> +	nframes = (unsigned int)div_u64(size, frame_size);
>  	if (nframes == 0 || nframes > UINT_MAX)
>  		return -EINVAL;
>  
> 


-- 
~Randy