[PATCH] ACPI: acenv: Permit compilation from within the kernel

[Rafael J. Wysocki]

On Tue, Nov 14, 2023 at 7:09 PM Sam Edwards <cfsworks at gmail.com> wrote:
>
> On 11/13/23 16:08, Linus Walleij wrote:
> > After commit a103f46633fd the kernel stopped compiling for
> > several ARM32 platforms that I am building with a bare metal
> > compiler. Bare metal compilers (arm-none-eabi-) don't
> > define __linux__.
>
> Hi Linus,
>
> I saw the same baremetal-compiler error here on the ARM64 side of the
> fence, and narrowed the problem to the same commit as you.
>
> >
> > This is because the header <acpi/platform/acenv.h> is now
> > in the include path for <linux/irq.h>:
>
> More generally, I think it's because of this addition to linux/acpi.h:
> +#include <linux/fw_table.h>
>
> linux/acpi.h is supposed to ensure _LINUX is defined (if it isn't
> already done by a non-baremetal compiler) before we start pulling in
> ACPICA includes, so that ACPICA knows the platform. But because
> fw_table.h contains:
> #include <linux/acpi.h>
> #include <acpi/acpi.h>
>
> ...the circular include does nothing (linux/acpi.h's include guard stops
> the include before _LINUX is defined) and we end up pulling in
> acpi/acpi.h before we're ready.

Yes, that's the problem AFAICS.  Dave?

What about moving the fw_table.h include in linux/acpi.h below the
mutex.h one, along with the EXPORT_SYMBOL_ACPI_LIB-related
definitions?

BTW, I'm not really sure why fw_table.h needs to include both
linux/acpi.h and acpi/acpi.h, because it should get the latter through
the former anyway.

> >
> >    CC      arch/arm/kernel/irq.o
> >    CC      kernel/sysctl.o
> >    CC      crypto/api.o
> > In file included from ../include/acpi/acpi.h:22,
> >                   from ../include/linux/fw_table.h:29,
> >                   from ../include/linux/acpi.h:18,
> >                   from ../include/linux/irqchip.h:14,
> >                   from ../arch/arm/kernel/irq.c:25:
> > ../include/acpi/platform/acenv.h:218:2: error: #error Unknown target environment
> >    218 | #error Unknown target environment
> >        |  ^~~~~
> >
> > One solution to make compilation with a bare metal compiler
> > work again is to say the file is used with Linux from within
> > the kernel if __KERNEL__ is defined so I did that.
>
> I am not an ACPI subsystem maintainer, but my understanding is that the
> files in include/acpi/ are copied verbatim from ACPICA, so any change to
> those files will have to be sent to the ACPICA project and wouldn't be
> accepted here.

There are exceptions, but generally you are right.

> More likely, we'd want to do something about the circular-include
> situation between linux/fw_table.h<->linux/acpi.h. That may have further
> consequences down the road than just our problem here. Perhaps just
> dropping both #includes from fw_table.h, and lowering the fw_table.h
> include from within linux/acpi.h to be below <acpi/acpi.h>, is the way
> to go?

Something like that.