Re: [PATCH] stubdom: foreignmemory: Fix build after 0dbb4be739c5

[Julien Grall <julien@xen.org>]

Hi Andrew,

On 13/07/2021 10:35, Andrew Cooper wrote:
> On 13/07/2021 10:27, Juergen Gross wrote:
>> On 13.07.21 11:20, Julien Grall wrote:
>>> From: Julien Grall <jgrall@amazon.com>
>>>
>>> Commit 0dbb4be739c5 add the inclusion of xenctrl.h from private.h and
>>> wreck the build in an interesting way:
>>>
>>> In file included from xen/stubdom/include/xen/domctl.h:39:0,
>>>                    from xen/tools/include/xenctrl.h:36,
>>>                    from private.h:4,
>>>                    from minios.c:29:
>>> xen/include/public/memory.h:407:5: error: expected
>>> specifier-qualifier-list before ‘XEN_GUEST_HANDLE_64’
>>>        XEN_GUEST_HANDLE_64(const_uint8) buffer;
>>>        ^~~~~~~~~~~~~~~~~~~
>>>
>>> This is happening because xenctrl.h defines __XEN_TOOLS__ and therefore
>>> the public headers will start to expose the non-stable ABI. However,
>>> xen.h has already been included by a mini-OS header before hand. So
>>> there is a mismatch in the way the headers are included.
>>>
>>> For now solve it in a very simple (and gross) way by including
>>> xenctrl.h before the mini-os headers.
>>>
>>> Fixes: 0dbb4be739c5 ("tools/libs/foreignmemory: Fix PAGE_SIZE
>>> redefinition error")
>>> Signed-off-by: Julien Grall <jgrall@amazon.com>
>>>
>>> ---
>>>
>>> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
>>>
>>> I couldn't find a better way with would not result to revert the patch
>>> (and break build on some system) or involve a longer rework of the
>>> headers.
>>
>> Just adding a "#define __XEN_TOOLS__" before the #include statements
>> doesn't work?
> 
> Not really, no.
> 
> libxenforeignmem has nothing at all to do with any Xen unstable
> interfaces.  Including xenctrl.h in the first place was wrong, because
> it is an unstable library.  By extension, the use of XC_PAGE_SIZE is
> also wrong.

Well... Previously we were using PAGE_SIZE which is just plain wrong on Arm.

At the moment, we don't have a way to query the page granularity of the 
hypervisor. But we know it can't change because of the way the current 
ABI was designed. Hence why using XC_PAGE_SIZE is the best of option we 
had until we go to ABIv2.

Cheers,

-- 
Julien Grall