linux-kernel - Re: [PATCH] pvcalls-front: 64-bit align flags

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Message-ID: <b7ec592a-bbd1-48d3-1a1f-92a8ed4a1e48@oracle.com>
Date:   Tue, 27 Feb 2018 16:19:33 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Stefano Stabellini <sstabellini@...nel.org>, jgross@...e.com
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pvcalls-front: 64-bit align flags

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@...reto.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.