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

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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>
This commit is contained in:
Masahiro Yamada
2022-09-25 03:19:14 +09:00
parent 4b09865900
commit 3216484550
29 changed files with 91 additions and 113 deletions
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6
scripts/Makefile.vmlinux_o
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@@ -18,7 +18,7 @@ quiet_cmd_gen_initcalls_lds = GEN $@
$(PERL) $(real-prereqs) > $@
.tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
$(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
$(call if_changed,gen_initcalls_lds)
targets := .tmp_initcalls.lds
@@ -48,7 +48,7 @@ quiet_cmd_ld_vmlinux.o = LD $@
cmd_ld_vmlinux.o = \
$(LD) ${KBUILD_LDFLAGS} -r -o $@ \
$(addprefix -T , $(initcalls-lds)) \
--whole-archive $(KBUILD_VMLINUX_OBJS) --no-whole-archive \
--whole-archive vmlinux.a --no-whole-archive \
--start-group $(KBUILD_VMLINUX_LIBS) --end-group \
$(cmd_objtool)
@@ -57,7 +57,7 @@ define rule_ld_vmlinux.o
$(call cmd,gen_objtooldep)
endef
vmlinux.o: $(initcalls-lds) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
vmlinux.o: $(initcalls-lds) vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
$(call if_changed_rule,ld_vmlinux.o)
targets += vmlinux.o