linux-kernel - [PATCH] kbuild: avoid build error when single DTB is turned into composite DTB

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Message-ID: <20240704131400.1501638-1-masahiroy@kernel.org>
Date: Thu,  4 Jul 2024 22:13:58 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: linux-kbuild@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>,
	Rob Herring <robh@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH] 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

The reason for the error is because $(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
the fdtoverlay tool.

Fixes: 15d16d6dadf6 ("kbuild: Add generic rule to apply fdtoverlay")
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 scripts/Makefile.lib | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index d78b5d38beaa..636119dc4403 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -407,8 +407,12 @@ cmd_dtc = $(HOSTCC) -E $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ;
 		-d $(depfile).dtc.tmp $(dtc-tmp) ; \
 	cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile)

+# NOTE:
+# Do not replace $(filter %.dtb %.dtbo, $^) with $(real-prereqs). When a single
+# DTB is turned into a multi-blob DTB, $^ will contain header file dependencies
+# recorded in the .*.cmd file.
 quiet_cmd_fdtoverlay = DTOVL   $@
-      cmd_fdtoverlay = $(objtree)/scripts/dtc/fdtoverlay -o $@ -i $(real-prereqs)
+      cmd_fdtoverlay = $(objtree)/scripts/dtc/fdtoverlay -o $@ -i $(filter %.dtb %.dtbo, $^)

 $(multi-dtb-y): FORCE
 	$(call if_changed,fdtoverlay)
-- 
2.43.0