Re: [PATCH v3 1/3] arch: add the macro COMPILE_OFFSETS to all the asm-offsets.c

[Menglong Dong]

On Wed, Aug 27, 2025 at 11:04 AM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Thu, Aug 21, 2025 at 2:38 AM Menglong Dong <menglong8.dong@xxxxxxxxx> wrote:
> >
> > The include/generated/asm-offsets.h is generated in Kbuild during
> > compiling from arch/SRCARCH/kernel/asm-offsets.c. When we want to
> > generate another similar offset header file, circular dependency can
> > happen.
>
> Is there a way to avoid all this churn?
>
> > For example, we want to generate a offset file include/generated/test.h,
> > which is included in include/sched/sched.h. If we generate asm-offsets.h
> > first, it will fail, as include/sched/sched.h is included in asm-offsets.c
>
> if so, may be don't add "static inline void migrate_disable()" to sched.h
> and instead add it to preempt.h and it will avoid this issue?

It's hard to avoid this churn. Take bounds.c for example, it defines
the macro __GENERATING_BOUNDS_H. For the header files that
it includes, it will exclude almost all the unnecessary code in
page-flags.h, mmzone.h if __GENERATING_BOUNDS_H is defined.
We can't use this approach, as it's hard to decide what to exclude
in sched.h.

We can't add migrate_disable or __migrate_disable to preempt.h,
as struct task is used in it, which is not available in preempt.h :/

I think this stuff can be reused in the feature if someone wants
to add such an offset.

Thanks!
Menglong Dong

>
> > and include/generated/test.h doesn't exist; If we generate test.h first,
> > it can't success neither, as include/generated/asm-offsets.h is included
> > by it.
> >
> > In x86_64, the macro COMPILE_OFFSETS is used to avoid such circular
> > dependency. We can generate asm-offsets.h first, and if the
> > COMPILE_OFFSETS is defined, we don't include the "generated/test.h".
> >
> > And we define the macro COMPILE_OFFSETS for all the asm-offsets.c for this
> > purpose.