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Subject: Re: [PATCH] pvcalls-front: 64-bit align flags
To: Stefano Stabellini <sstabellini@kernel.org>, jgross@suse.com
Cc: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org
References: <alpine.DEB.2.10.1802271150020.4239@sstabellini-ThinkPad-X260>
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <b7ec592a-bbd1-48d3-1a1f-92a8ed4a1e48@oracle.com>
Date: Tue, 27 Feb 2018 16:19:33 -0500
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On 02/27/2018 02:54 PM, Stefano Stabellini wrote:
> We are using test_and_* operations on the status and flag fields of
> struct sock_mapping. However, these functions require the operand to be
> 64-bit aligned on arm64. Currently, only status is 64-bit aligned.
>
> Make flags 64-bit aligned by introducing an explicit padding field.
>
> Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
>
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index ca5b773..aa07b2a 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -78,6 +78,7 @@ struct sock_mapping {
>  #define PVCALLS_STATUS_BIND          1
>  #define PVCALLS_STATUS_LISTEN        2
>  			uint8_t status;
> +			uint8_t pad[7];

Does this guarantee alignment (for either status or flag)?

-boris

>  		/*
>  		 * Internal state-machine flags.
>  		 * Only one accept operation can be inflight for a socket.