Messages in this thread | | | Date | Tue, 27 Feb 2018 13:32:32 -0800 (PST) | From | Stefano Stabellini <> | Subject | Re: [PATCH] pvcalls-front: 64-bit align flags |
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On Tue, 27 Feb 2018, Boris Ostrovsky wrote: > 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)?
Yes: status is part of a struct and a union. Unions and structs have the alignment of their most aligned type. In this case they are 64-bit aligned, as some of the fields are pointers.
The padding makes sure that flags is 1+7 bytes from it.
> > /* > > * Internal state-machine flags. > > * Only one accept operation can be inflight for a socket. >
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