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Re: [PATCH v2] xen/public: fix flexible array definitions


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: Juergen Gross <jgross@xxxxxxxx>
  • Date: Thu, 30 Nov 2023 14:28:44 +0100
  • Authentication-results: smtp-out1.suse.de; none
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  • Cc: George Dunlap <george.dunlap@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
  • Delivery-date: Thu, 30 Nov 2023 13:28:51 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 30.11.23 12:34, Andrew Cooper wrote:
On 30/11/2023 9:21 am, Juergen Gross wrote:
Flexible arrays in public headers can be problematic with some
compilers.

With XEN_FLEX_ARRAY_DIM there is a mechanism available to deal with
this issue, but care must be taken to not change the affected structs
in an incompatible way.

So bump __XEN_LATEST_INTERFACE_VERSION__ and introduce a new macro
XENPV_FLEX_ARRAY_DIM which will be XENPV_FLEX_ARRAY_DIM with the
interface version being new enough and "1" (the value used today in
the affected headers) when the interface version is an old one.

Replace the arr[1] instances (this includes the ones seen to be
problematic in recent Linux kernels [1]) with arr[XENPV_FLEX_ARRAY_DIM]
in order to avoid compilation errors.

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=217693

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

CHANGELOG please.  This change, however it ends up looking, absolutely
needs covering.

Would this be fine:

 ### Changed
+ - Changed flexible array definitions in public I/O interface headers to not
+   use "1" as the number of array elements.


Juergen

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