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

>
> 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.

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?

Kind regards,
Sam

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