Re: [PATCH v2 1/4] Use an include/boot directory to override headers for boot code

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.12.2024 15:29, Frediano Ziglio wrote:
> On Tue, Dec 10, 2024 at 10:14 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 22.11.2024 10:33, Frediano Ziglio wrote:
>>> Not all headers can be used by 32 bit boot code.
>>> Allows to override some headers, we don't want to mess up with
>>> main headers as most of the code is only 64 bit so the easy stuff should
>>> be done for 64 bit declarations.
>>> Boot headers should be 64 bit compatibles to avoid having multiple
>>> declarations.
>>
>> I'm afraid that in isolation it's not clear what is intended. Boot code is
>> all located in a single directory. Can't we use local headers there, using
>> #include "...", instead of ...
>>
> 
> That approach was refused.

Can you provide a reference please?

> Some definitions are in the headers (like
> CPU features for instance) but duplicating the definitions was
> rejected as a solution.
> So the idea is to reuse such definitions. But, as stated in the
> comment, the "x86" includes are not for x86, but most of them are just
> for x64.This for historic reasons. But most of the code is x64 only so
> changing headers to be x86 compatible would complicate them for a
> minimal gain.

Yet the amount of what wants sharing ought to be low. It might even help
to clarify what it is that is meant to become shared.

>>> --- a/xen/arch/x86/boot/Makefile
>>> +++ b/xen/arch/x86/boot/Makefile
>>> @@ -18,7 +18,7 @@ CFLAGS_x86_32 := $(subst -m64,-m32 
>>> -march=i686,$(XEN_TREEWIDE_CFLAGS))
>>>  $(call cc-options-add,CFLAGS_x86_32,CC,$(EMBEDDED_EXTRA_CFLAGS))
>>>  CFLAGS_x86_32 += -Werror -fno-builtin -g0 -msoft-float -mregparm=3
>>>  CFLAGS_x86_32 += -nostdinc -include $(filter 
>>> %/include/xen/config.h,$(XEN_CFLAGS))
>>> -CFLAGS_x86_32 += $(filter -I% -O%,$(XEN_CFLAGS)) -D__XEN__
>>> +CFLAGS_x86_32 += -I$(srctree)/arch/x86/include/boot $(filter -I% 
>>> -O%,$(XEN_CFLAGS)) -D__XEN__
>>
>> ... introducing a arch-wide subdir, which non-boot code could easily (ab)use?
> 
> You would have to explicitly add the "boot" into the path,

No different from "hvm" or "guest", just to give two examples.

> it does not
> seem "easy" to me, but if you really want to do it you can do with
> these or any other headers, like simply "#include "../arch/arm/..." in
> x64 code. Same easiness.

Well, no, the ".." in #include directives certainly stands out.

Jan