Re: [XEN PATCH] build: Fix x86 build without EFI

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.08.2022 17:43, Anthony PERARD wrote:
> On Tue, Aug 16, 2022 at 03:02:10PM +0200, Jan Beulich wrote:
>> On 16.08.2022 12:30, Anthony PERARD wrote:
>>> We can't have a source file with the same name that exist in both the
>>> common code and in the arch specific code for efi/. This can lead to
>>> comfusion in make and it can pick up the wrong source file. This issue
>>> lead to a failure to build a pv-shim for x86 out-of-tree, as this is
>>> one example of an x86 build using the efi/stub.c.
>>>
>>> The issue is that in out-of-tree, make might find x86/efi/stub.c via
>>> VPATH, but as the target needs to be rebuilt due to FORCE, make
>>> actually avoid changing the source tree and rebuilt the target with
>>> VPATH ignored, so $@ lead to the build tree where "stub.c" dosen't
>>> exist yet so a link is made to "common/stub.c".
>>>
>>> Rework the new common/stub.c file to have a different name than the
>>> already existing one. And build both *stub.c as two different objects.
>>> This mean we have to move some efi_compat_* aliases which are probably
>>> useless for Arm.
>>
>> These useless aliases want avoiding there imo. Already when the original
>> series was discussed, I requested to avoid introduction of a file named
>> common-stub.c or alike.
> 
> Yeah, I've notice that. This is why the build is broken under
> specific condition.
> 
>> If names need to be different, can't we follow
>> boot.c's model and introduce a per-arch efi/stub.h which stub.c would
>> include at a suitable position (and which right now would be empty for
>> Arm)?
> 
> That seems to be possible. But how is it better than having two
> different source file? The only thing is to avoid exporting the
> efi_compat_* symbol aliases.

As said - I think they're wrong to have in Arm. But if Arm maintainers
don't care about them being there, so be it. As long as they don't
voice a view, I guess as the EFI maintainer I can sensibly ask for
them to be avoided in a reasonably clean way.

> The downside is we would have another weird
> looking not really header which is actually just part of a source file.
> At least, "stub.c" and "stub.h" would be two different names, we just
> change the extension rather than the basename.

Whether that's "weird" is certainly a matter of taste ... To me,
common-stub.c also comes close  to "weird", fwiw. But as I've tried
to express, if I'm the only one disliking common-stub.c, then please
ignore my view and I'll nevertheless ack the resulting patch. (That
said, I view the vpath issue causing the problem as really the one
that would want tackling. There shouldn't be a requirement for
files to have different names as long as they live in different
directories.)

Jan