Re: [RFC] kbuild - introduce vdir to make life easier for x86_64

[Sam Ravnborg <sam@ravnborg.org>]

Hi Ingo 
> 
> i'd like to add it here that Makefile polishing is important - it's just 
> that in the context of arch/*x86* the Makefile impact of the current 
> cross-arch code sharing practice is one of the smaller problems and the 
> Makefiles get cleaned up via the arch/x86 merge anyway.

Partly so. Took a look at the x86 tree.
The main Makefile are at least not merged. Neither are pci/Makefile not
boot/compressed/Makefile.
And some of the rest of the Makefiles are not pretty with the huge arch 
specific sections ifdeffed out.

I have long thought about some extensions to the kbuild 'language'
along the following lines:

Additional shorthands for obj-m:
obj-m-if-m
obj-m-if-y   
obj-m-ifn-

Additional shorthands for obj-y:
obj-y-if-m
obj-y-if-y
obj-y-ifn-

The ifn- versions are to test for empty options.

This may as an example result in following changes to the 
acpi/Makefile in the merged tree:

 Makefile |   14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/acpi/Makefile b/arch/x86/kernel/acpi/Makefile
index ad4baa6..ec5a295 100644
--- a/arch/x86/kernel/acpi/Makefile
+++ b/arch/x86/kernel/acpi/Makefile
@@ -1,15 +1,11 @@
 obj-$(CONFIG_ACPI)		+= boot.o
 
-ifeq ($(CONFIG_X86_32),y)
 ifneq ($(CONFIG_PCI),)
-obj-$(CONFIG_X86_IO_APIC)	+= earlyquirk.o
-endif
-obj-$(CONFIG_ACPI_SLEEP)	+= sleep_32.o wakeup_32.o
-else
-obj-$(CONFIG_ACPI_SLEEP)	+= sleep_64.o wakeup_64.o
+obj-$(CONFIG_X86_32)-if-$(CONFIG_X86_IO_APIC) += sleep_32.o wakeup_32.o
 endif
 
-ifneq ($(CONFIG_ACPI_PROCESSOR),)
-obj-y				+= cstate.o processor.o
-endif
+obj-$(CONFIG_X86_32)-if-$(CONFIG_ACPI_SLEEP) += sleep_32.o wakeup_32.o
+obj-$(CONFIG_X86_64)-if-$(CONFIG_ACPI_SLEEP) += sleep_64.o wakeup_64.o
+
+obj-y-if-$(CONFIG_ACPI_PROCESSOR) += cstate.o processor.o


My biggest worry is that we end up with a more compact format
but only me (and a very few others) can read it.
But I think the above could make the x86 Makefiles more readable
as a whole.

	Sam