[PATCH] 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. Note
though this therotically affects all architectures, ones except RISC-V
may not reproduce similar errors since there are no source files
directly under arch/*/cpu, thus the extra include doesn't hurt.

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

I was surprised to see this morning's CI passed[1] even for these RISC-V
boards. Builds for SiFive unleashed, QEMU S-Mode virt and Sipeed Lichee
Pi 4A always fail on my machine with the latest master branch, thus
maybe I missed some points when digging the issue, please correct me if
so.

[1]: https://source.denx.de/u-boot/u-boot/-/commit/3833600dbaa2d7008063f3127abf21be8f0fe6cd/pipelines?ref=master

 Makefile | 2 --
 1 file changed, 2 deletions(-)

diff --git a/Makefile b/Makefile
index da53efa09f1..b610dcc0b6e 100644
--- a/Makefile
+++ b/Makefile
@@ -724,8 +724,6 @@ endif
 ARCH_CPPFLAGS :=
 ARCH_AFLAGS :=
 ARCH_CFLAGS :=
-# Modified for U-Boot
--include arch/$(SRCARCH)/Makefile
 
 ifeq ($(dot-config),1)
 ifeq ($(may-sync-config),1)
-- 
2.50.0