Re: [PATCH 2/6] x86/mm: p2m_add_foreign() is HVM-only

[Jan Beulich <jbeulich@xxxxxxxx>]

On 08.01.2021 17:38, Oleksandr wrote:
> On 05.01.21 10:48, Jan Beulich wrote:
>> On 04.01.2021 17:57, Oleksandr Tyshchenko wrote:
>>> Hello all.
>>>
>>> [Sorry for the possible format issues]
>>>
>>> On Tue, Dec 22, 2020 at 12:41 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>> wrote:
>>>
>>>> On 21/12/2020 08:10, Jan Beulich wrote:
>>>>> On 17.12.2020 20:18, Andrew Cooper wrote:
>>>>>> On 15/12/2020 16:26, Jan Beulich wrote:
>>>>>>> This is together with its only caller, xenmem_add_to_physmap_one().
>>>>>> I can't parse this sentence.  Perhaps "... as is it's only caller," as a
>>>>>> follow-on from the subject sentence.
>>>>>>
>>>>>>>   Move
>>>>>>> the latter next to p2m_add_foreign(), allowing this one to become
>>>> static
>>>>>>> at the same time.
>>>>>>>
>>>>>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>>>> Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>>> So I had to ask Andrew to revert this (I was already at home when
>>>>> noticing the breakage), as it turned out to break the shim build.
>>>>> The problem is that xenmem_add_to_physmap() is non-static and
>>>>> hence can't be eliminated altogether by the compiler when !HVM.
>>>>> We could make the function conditionally static
>>>>> "#if !defined(CONFIG_X86) && !defined(CONFIG_HVM)", but this
>>>>> looks uglier to me than this extra hunk:
>>>>>
>>>>> --- unstable.orig/xen/common/memory.c
>>>>> +++ unstable/xen/common/memory.c
>>>>> @@ -788,7 +788,11 @@ int xenmem_add_to_physmap(struct domain
>>>>>       union add_to_physmap_extra extra = {};
>>>>>       struct page_info *pages[16];
>>>>>
>>>>> -    ASSERT(paging_mode_translate(d));
>>>>> +    if ( !paging_mode_translate(d) )
>>>>> +    {
>>>>> +        ASSERT_UNREACHABLE();
>>>>> +        return -EACCES;
>>>>> +    }
>>>>>
>>>>>       if ( xatp->space == XENMAPSPACE_gmfn_foreign )
>>>>>           extra.foreign_domid = DOMID_INVALID;
>>>>>
>>>>> Andrew, please let me know whether your ack stands with this (or
>>>>> said alternative) added, or whether you'd prefer me to re-post.
>>>> Yeah, this is probably neater than the ifdefary.  My ack stands.
>>>>
>>>> ~Andrew
>>>>
>>> I might miss something or did incorrect tests, but ...
>>> ... trying to build current staging
>>> (7ba2ab495be54f608cb47440e1497b2795bd301a) for x86 (with # CONFIG_HVM is
>>> not set) I got the following:
>>>
>>> /media/b/build/build/tmp/work/x86_64-xt-linux/domd-image-weston/1.0-r0/repo/build/tmp/work/aarch64-poky-linux/xen/4.14.0+gitAUTOINC+2c6e5a8ceb-r0/git/xen/common/memory.c:941:
>>> undefined reference to `xenmem_add_to_physmap_one'
>>> /media/b/build/build/tmp/work/x86_64-xt-linux/domd-image-weston/1.0-r0/repo/build/tmp/work/aarch64-poky-linux/xen/4.14.0+gitAUTOINC+2c6e5a8ceb-r0/git/xen/common/memory.c:941:(.text+0x1e391):
>>> relocation truncated to fit: R_X86_64_PC32 against undefined symbol
>>> `xenmem_add_to_physmap_one'
>>> ld:
>>> /media/b/build/build/tmp/work/x86_64-xt-linux/domd-image-weston/1.0-r0/repo/build/tmp/work/aarch64-poky-linux/xen/4.14.0+gitAUTOINC+2c6e5a8ceb-r0/git/xen/.xen-syms.0:
>>> hidden symbol `xenmem_add_to_physmap_one' isn't defined
>>> ld: final link failed: Bad value
>>>
>>> It is worth mentioning that I do not use pvshim_defconfig (I disable HVM
>>> support via menuconfig manually before building).
>> The specific .config may matter. The specific compiler version may
>> also matter. Things work fine for me, both for the shim config and
>> a custom !HVM one, with gcc10.
> 
> ok, after updating my a little bit ancient compiler to the latest 
> possible (?) on xenial gcc-9 the build issue had gone away. Sorry for 
> the noise.

There's no reason to be sorry - we want Xen to build with a wide
range of compiler versions. It's just that if a build issue is
version dependent, it is often up to the person running into it
to determine how to address the issue (and submit a patch).

Jan