kbuild: use obj-y instead extra-y for objects placed at the head

The objects placed at the head of vmlinux need special treatments:

 - arch/$(SRCARCH)/Makefile adds them to head-y in order to place
   them before other archives in the linker command line.

 - arch/$(SRCARCH)/kernel/Makefile adds them to extra-y instead of
   obj-y to avoid them going into built-in.a.

This commit gets rid of the latter.

Create vmlinux.a to collect all the objects that are unconditionally
linked to vmlinux. The objects listed in head-y are moved to the head
of vmlinux.a by using 'ar m'.

With this, arch/$(SRCARCH)/kernel/Makefile can consistently use obj-y
for builtin objects.

There is no *.o that is directly linked to vmlinux. Drop unneeded code
in scripts/clang-tools/gen_compile_commands.py.

$(AR) mPi needs 'T' to workaround the llvm-ar bug. The fix was suggested
by Nathan Chancellor [1].

[1]: https://lore.kernel.org/llvm/YyjjT5gQ2hGMH0ni@dev-arch.thelio-3990X/

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/xtensa/kernel/Makefile b/arch/xtensa/kernel/Makefile
index 897c1c741058..f28b8e3d717e 100644
--- a/arch/xtensa/kernel/Makefile
+++ b/arch/xtensa/kernel/Makefile
@@ -3,9 +3,9 @@
 # Makefile for the Linux/Xtensa kernel.
 #
 
-extra-y := head.o vmlinux.lds
+extra-y := vmlinux.lds
 
-obj-y := align.o coprocessor.o entry.o irq.o platform.o process.o \
+obj-y := head.o align.o coprocessor.o entry.o irq.o platform.o process.o \
 	 ptrace.o setup.o signal.o stacktrace.o syscall.o time.o traps.o \
 	 vectors.o