Re: [PATCH 1/2] x86: move arch_generic_hweightl() to arch-specific library

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/11/2025 1:58 pm, Jan Beulich wrote:
> On 26.11.2025 14:51, Andrew Cooper wrote:
>> On 26/11/2025 1:24 pm, Jan Beulich wrote:
>>> diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk
>>> index 16368a498bb7..a0ee050c931b 100644
>>> --- a/xen/arch/x86/arch.mk
>>> +++ b/xen/arch/x86/arch.mk
>>> @@ -3,6 +3,8 @@
>>>  
>>>  export XEN_IMG_OFFSET := 0x200000
>>>  
>>> +ALL_LIBS-y += arch/x86/lib/lib.a
>>> +
>> Oh, I'd realised it was this easy, I'd have done so straight away when
>> adding x86's custom arch_generic_hweightl().
>>
>> I assumed it was going to be more complicated getting the order of the
>> arch specific lib correct with the generic lib.
>>
>> More concretely.  Given an x86 lib, we should move things like
>> arch/x86/memcpy.S to it.
>>
>> Therefore, when we have common/lib.a and arch/lib.a, do we guarantee to
>> have arch/lib.a with higher precedence so for matching functions the
>> arch specific one guarantees to be taken?
> Not with the change above, it would need to become
>
> ALL_LIBS-y := arch/x86/lib/lib.a $(ALL_LIBS-y)
>
> to achieve that, requiring that ALL_LIBS-y won't change into a lazy-expansion
> variable. If that's okay (please confirm), I can adjust the patch.
>
> Things would be yet easier if every arch had a lib/lib.a, as then in
> xen/Makefile we could simply have
>
> ALL_LIBS-y                := arch/$(SRCARCH)/lib/lib.a
> ALL_LIBS-y                += lib/lib.a
>
> Alternatively we could move the setting of ALL_LIBS-y in xen/Makefile to
> after the arch/$(SRCARCH)/arch.mk inclusion. I'd be a little wary of that,
> though, as it would then be different from ALL_OBJS-y.

I think this would be better handled by common code.

Arches are going to want a lib.a eventually.  ARM even has
arch/arm/arm{32,64}/lib/ but like x86 they're just simple obj-y += at
the moment.

However, arches shouldn't be forced to make an empty one simply to build.

Does this work:

ALL_LIBS-y                := $(wildcard arch/$(SRCARCH)/lib/lib.a)
ALL_LIBS-y                += lib/lib.a

?  If so, I think it's the nicest option.

~Andrew