Re: [PATCH v5 04/13] xen/arm64: Split and move MMU-specific head.S to mmu/head.S

[Henry Wang <Henry.Wang@xxxxxxx>]

Hi Julien,

> On Aug 21, 2023, at 18:16, Julien Grall <julien@xxxxxxx> wrote:
> On 21/08/2023 10:29, Henry Wang wrote:
>>> On Aug 21, 2023, at 17:18, Julien Grall <julien@xxxxxxx> wrote:
>>> On 14/08/2023 05:25, Henry Wang wrote:
>>>> The MMU specific code in head.S will not be used on MPU systems.
>>>> Instead of introducing more #ifdefs which will bring complexity
>>>> to the code, move MMU related code to mmu/head.S and keep common
>>>> code in head.S. Two notes while moving:
>>>> - As "fail" in original head.S is very simple and this name is too
>>>>   easy to be conflicted, duplicate it in mmu/head.S instead of
>>>>   exporting it.
>>>> - Use ENTRY() for enable_secondary_cpu_mm, enable_boot_cpu_mm and
>>>>   setup_fixmap to please the compiler after the code movement.
>>> 
>>> I am not sure I understand why you are saying "to please the compiler" 
>>> here. Isn't it necessary for the linker (not the compiler) to find the 
>>> function? And therefore there is no pleasing (as in this is not a bug in 
>>> the toolchain).
>> Yes it meant to be linker, sorry for the confusion. What I want to express is
>> without the ENTRY(), for example if we remove the ENTRY() around the
>> setup_fixmap(), we will have:
>> ```
>> aarch64-none-linux-gnu-ld: prelink.o: in function `primary_switched':
>> /home/xinwan02/repos_for_development/xen_playground/xen/xen/arch/arm/arm64/head.S:278:
>>  undefined reference to `setup_fixmap'
>> /home/xinwan02/repos_for_development/xen_playground/xen/xen/arch/arm/arm64/head.S:278:(.text.header+0x1a0):
>>  relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol 
>> `setup_fixmap'
>> make[2]: *** [arch/arm/Makefile:95: xen-syms] Error 1
>> make[1]: *** [build.mk:90: xen] Error 2
>> make: *** [Makefile:598: xen] Error 2
>> ```
>> I will use the word “linker” in v6 if you agree.
> 
> The sentence also need to be reworded. How about:
> 
> "Use ENTRY() for ... as they will be used externally."

Sure, I will use the suggested sentence.

> 
>>> 
>>> Other than that, the split looks good to me.
>> May I please take this as a Reviewed-by tag? I will add the tag if you are
>> happy with that.
> 
> Sure. Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>

Thanks!

Kind regards,
Henry

> 
> Cheers,
> 
> -- 
> Julien Grall