tjh.dev
kbuild: avoid build error when single DTB is turned into composite DTB
As commit afa974b77128 ("kbuild: add real-prereqs shorthand for
$(filter-out FORCE,$^)") explained, $(real-prereqs) is not just a list
of objects when linking a multi-object module. If a single-object module
is turned into a multi-object module, $^ (and therefore $(real-prereqs)
as well) contains header files recorded in the *.cmd file. Such headers
must be filtered out.
Now that a DTB can be built either from a single source or multiple
source files, the same issue can occur.
Consider the following scenario:
First, foo.dtb is implemented as a single-blob device tree.
The code looks something like this:
[Sample Code 1]
Makefile:
dtb-y += foo.dtb
foo.dts:
#include <dt-bindings/gpio/gpio.h>
/dts-v1/;
/ { };
When it is compiled, .foo.dtb.cmd records that foo.dtb depends on
scripts/dtc/include-prefixes/dt-bindings/gpio/gpio.h.
Later, foo.dtb is split into a base and an overlay. The code looks
something like this:
[Sample Code 2]
Makefile:
dtb-y += foo.dtb
foo-dtbs := foo-base.dtb foo-addon.dtbo
foo-base.dts:
#include <dt-bindings/gpio/gpio.h>
/dts-v1/;
/ { };
foo-addon.dtso:
/dts-v1/;
/plugin/;
/ { };
If you rebuild foo.dtb without 'make clean', you will get this error:
Overlay 'scripts/dtc/include-prefixes/dt-bindings/gpio/gpio.h' is incomplete
$(real-prereqs) contains not only foo-base.dtb and foo-addon.dtbo but
also scripts/dtc/include-prefixes/dt-bindings/gpio/gpio.h, which is
passed to scripts/dtc/fdtoverlay.
Fixes: 15d16d6dadf6 ("kbuild: Add generic rule to apply fdtoverlay")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>