lkml.org 
[lkml]   [2018]   [Feb]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] pvcalls-front: 64-bit align flags
From
Date
On 02/27/2018 04:32 PM, Stefano Stabellini wrote:
> 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.

OK.

What about adding __attribute__((aligned(8))) to both (with a comment
explaining reasoning)?

-boris


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

\
 
 \ /
  Last update: 2018-02-27 22:44    [W:0.049 / U:0.456 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site