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 17:18, Julien Grall <julien@xxxxxxx> wrote:
> 
> Hi Henry,
> 
> 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.

> 
> 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.

Kind regards,
Henry

> 
> Cheers,
> 
> -- 
> Julien Grall