kbuild: Add objtool to top-level clean target

Objtool is an integral part of the build, make sure it gets cleaned by
"make clean" and "make mrproper".

Fixes: 442f04c ("objtool: Add tool to perform compile-time stack metadata validation")
Reported-by: Jens Remus <jremus@linux.ibm.com>
Closes: https://lore.kernel.org/15f2af3b-be33-46fc-b972-6b8e7e0aa52e@linux.ibm.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Tested-by: Jens Remus <jremus@linux.ibm.com>
Link: https://patch.msgid.link/968faf2ed30fa8b3519f79f01a1ecfe7929553e5.1770759919.git.jpoimboe@kernel.org
[nathan: use Closes: instead of Link: per checkpatch.pl]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: jpoimboe

Makefile

@@ -1481,6 +1481,15 @@ ifneq ($(wildcard $(resolve_btfids_O)),)
 	$(Q)$(MAKE) -sC $(srctree)/tools/bpf/resolve_btfids O=$(resolve_btfids_O) clean
 endif
 
+PHONY += objtool_clean
+
+objtool_O = $(abspath $(objtree))/tools/objtool
+
+objtool_clean:
+ifneq ($(wildcard $(objtool_O)),)
+	$(Q)$(MAKE) -sC $(abs_srctree)/tools/objtool O=$(objtool_O) srctree=$(abs_srctree) clean
+endif
+
 tools/: FORCE
 	$(Q)mkdir -p $(objtree)/tools
 	$(Q)$(MAKE) O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/
@@ -1644,7 +1653,7 @@ vmlinuxclean:
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean
 	$(Q)$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) clean)
 
-clean: archclean vmlinuxclean resolve_btfids_clean
+clean: archclean vmlinuxclean resolve_btfids_clean objtool_clean
 
 # mrproper - Delete all generated files, including .config
 #

tools/objtool/Makefile

@@ -29,6 +29,8 @@ srctree := $(patsubst %/,%,$(dir $(CURDIR)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
 endif
 
+RM ?= rm -f
+
 LIBSUBCMD_DIR = $(srctree)/tools/lib/subcmd/
 ifneq ($(OUTPUT),)
   LIBSUBCMD_OUTPUT = $(abspath $(OUTPUT))/libsubcmd