objtool: Fix seg fault with gold linker

Objtool segfaults when the gold linker is used with
CONFIG_MODVERSIONS=y and CONFIG_UNWINDER_ORC=y.

With CONFIG_MODVERSIONS=y, the .o file gets passed to the linker before
being passed to objtool. The gold linker seems to strip unused ELF
symbols by default, which confuses objtool and causes the seg fault when
it's trying to generate ORC metadata.

Objtool should really be running immediately after GCC anyway, without a
linker call in between. Change the makefile ordering so that objtool is
called before the linker.

Reported-and-tested-by: Markus <[e-mail]>
Signed-off-by: Josh Poimboeuf <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

scripts/Makefile.build

···
 objtool_args += $(call cc-ifversion, -lt, 0405, --no-unreachable)
 endif
 
+ifdef CONFIG_MODVERSIONS
+objtool_o = $(@D)/.tmp_$(@F)
+else
+objtool_o = $(@)
+endif
+
 # 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file
 cmd_objtool = $(if $(patsubst y%,, \
 	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
-	$(__objtool_obj) $(objtool_args) "$(@)";)
+	$(__objtool_obj) $(objtool_args) "$(objtool_o)";)
 objtool_obj = $(if $(patsubst y%,, \
 	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
 	$(__objtool_obj))
···
 define rule_cc_o_c
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
 	$(call cmd_and_fixdep,cc_o_c)					  \
-	$(cmd_modversions_c)						  \
 	$(call echo-cmd,objtool) $(cmd_objtool)				  \
+	$(cmd_modversions_c)						  \
 	$(call echo-cmd,record_mcount) $(cmd_record_mcount)
 endef
 
 define rule_as_o_S
 	$(call cmd_and_fixdep,as_o_S)					  \
-	$(cmd_modversions_S)						  \
-	$(call echo-cmd,objtool) $(cmd_objtool)
+	$(call echo-cmd,objtool) $(cmd_objtool)				  \
+	$(cmd_modversions_S)
 endef
 
 # List module undefined symbols (or empty line if not enabled)