[PATCH v2] kbuild: Avoid including architecture-specific Makefile twice

[Yao Zi]

Stranges errors are observed when building U-Boot master for almost any
RISC-V board, the messages are in two types, one is about duplicated
symbols,

	u-boot/arch/riscv/cpu//mtrap.S:32: multiple definition of `trap_entry';
	arch/riscv/cpu/mtrap.o: u-boot/arch/riscv/cpu//mtrap.S:32: first defined here

and the other is fixdep's complaint about missing dependency files,

	fixdep: error opening file: arch/riscv/cpu/.mtrap.o.d: No such file or directory
	fixdep: error opening file: arch/riscv/cpu//.start.o.d: No such file or directory

where the latter could only be reproduced when building parallelly.

Both the two types of errors are about files in arch/riscv/cpu, and
there's a suspicious slash character in the reported path. Looking
through RISC-V-specific Makefiles, there's only one place that may
expand to such a path,

	libs-y += arch/riscv/cpu/$(CPU)/

The right hand expands to "arch/riscv/cpu//" if $(CPU) isn't defined at
the time of including. With some debug statement added to
arch/riscv/Makefile, the output proves that arch/riscv/Makefile is
included twice, once with $(CPU) undefined and once defined correctly
according to CONFIG_SYS_CPU.

Futher bisecting shows an extra include statement against
arch/$(SRCARCH)/Makefile is added in earlier bump of Kbuild system. But
the statement is evaluated before config.mk is included and definition
of $(CPU), causing objects in arch/riscv/cpu/ are built and linked twice
(once as "arch/riscv/cpu/*", and once as "arch/riscv/cpu//*"), resulting
in the error.

Let's simply remove the extra include to fix these nasty errors. For
config targets, bumping Kbuild also introduced a new include to
arch/$(SRCARCH)/Makefile, which is removed as well for consistency.

Fixes: 5f520875bdf ("kbuild: Bump the build system to 5.1")
Signed-off-by: Yao Zi <ziyao at disroot.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---

Changes from v1
- Don't describe the problem as RISC-V-specific since it may affect ARM
  builds as well.
- Prevent config targets from including for architecture-specific
  Makefile as well for consistency.
- Add comments to explain the removal.
- Link to v1: https://lore.kernel.org/u-boot/20250709161418.21287-2-ziyao@disroot.org/

 Makefile | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index da53efa09f1..e745cc618ba 100644
--- a/Makefile
+++ b/Makefile
@@ -635,8 +635,9 @@ ifeq ($(config-targets),1)
 # Read arch specific Makefile to set KBUILD_DEFCONFIG as needed.
 # KBUILD_DEFCONFIG may point out an alternative default configuration
 # used for 'make defconfig'
-# Modified for U-Boot
--include arch/$(SRCARCH)/Makefile
+# Modified for U-Boot: we don't include arch/$(SRCARCH)/Makefile for config
+# targets, which is useless since U-Boot has no architecture defining its own
+# KBUILD_{DEF,K}CONFIG, or CROSS_COMPILE.
 export KBUILD_DEFCONFIG KBUILD_KCONFIG CC_VERSION_TEXT
 
 config: scripts_basic outputmakefile FORCE
@@ -724,8 +725,10 @@ endif
 ARCH_CPPFLAGS :=
 ARCH_AFLAGS :=
 ARCH_CFLAGS :=
-# Modified for U-Boot
--include arch/$(SRCARCH)/Makefile
+# Modified for U-Boot: we put off the include of arch/$(SRCARCH)/Makefile until
+# making sure include/config/auto.conf is up-to-date and include of config.mk,
+# because the architecture-specific Makefile may make use of variables defined
+# in config.mk. See also the comment about autoconf_is_old.
 
 ifeq ($(dot-config),1)
 ifeq ($(may-sync-config),1)
-- 
2.50.0