Re: [RFC?] xen/arm: memaccess: Pass struct npfec by reference in p2m_mem_access_check

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, Nov 25, 2021 at 5:49 PM Oleksandr Tyshchenko
<olekstysh@xxxxxxxxx> wrote:
>
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>
> Today I noticed a "note" when building Xen on Arm64 with
> aarch64-poky-linux-gcc (GCC) 9.3.0. It turned out that Andrew Cooper
> had alredy reported it before [1]:
>
> mem_access.c: In function 'p2m_mem_access_check':
> mem_access.c:227:6: note: parameter passing for argument of type
> 'const struct npfec' changed in GCC 9.1
>   227 | bool p2m_mem_access_check(paddr_t gpa, vaddr_t gla,
>                                   const struct npfec npfec)
>
> From the explanation I understand that nothing bad actually is going
> to happen in our case, it is harmless and shown to only draw our
> attention that the ABI changed due to bug (with passing bit-fields
> by value) fixed in GCC 9.1. This information doesn't mean much for us
> as Xen is an embedded project with no external linkage. But, of course,
> it would be better to eliminate the note. You can also find related
> information about the bug at [2].
>
> So make the note go away by passing bit-fields by reference.
>
> [1] https://www.mail-archive.com/xen-devel@xxxxxxxxxxxxxxxxxxxx/msg87439.html
> [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88469
>
> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Acked-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>