kbuild: improve linker compatibility with lib-ksyms.o build

lib-ksyms.o is created by linking an empty input file with a linker script containing the interesting bits. Currently the empty input file is an archive containing nothing, however this causes the gold linker to segfault.

I have opened a bug against gold

https://sourceware.org/bugzilla/show_bug.cgi?id=20767

However this can be worked around by assembling an empty file to link with instead. The resulting lib-ksyms.o is slightly larger (seemingly due to empty .text, .data, .bss setions added), but final linked output should not be changed.

---

Hi Michal,

If we can sneak this into 4.9 it would be nice, so we don't have a release version of the kernel out there with this bug.

Thanks,
Nick

 scripts/Makefile.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 05c6bb4..fc6ebe4 100644
@@ -490,7 +490,7 @@ quiet_cmd_export_list = EXPORTS $@
 cmd_export_list = $(OBJDUMP) -h $< | \
 	sed -ne '/___ksymtab/{s/.*+/$(ref_prefix)/;s/ .*/)/;p}' >$(ksyms-lds);\
 	rm -f $(dummy-object);\
-	$(AR) rcs$(KBUILD_ARFLAGS) $(dummy-object);\
+	echo | $(CC) $(a_flags) -c -o $(dummy-object) -x assembler -;\
 	$(LD) $(ld_flags) -r -o $@ -T $(ksyms-lds) $(dummy-object);\
 	rm $(dummy-object) $(ksyms-lds)
 

2.9.3