objtool/klp: Only enable --checksum when needed

With CONFIG_KLP_BUILD enabled, checksums are only needed during a
klp-build run. There's no need to enable them for normal kernel builds.

This also has the benefit of softening the xxhash dependency.

Signed-off-by: Josh Poimboeuf <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Tested-by: Michael Kelley <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

arch/x86/boot/startup/Makefile

···
 # relocations, even if other objtool actions are being deferred.
 #
 $(pi-objs): objtool-enabled	= 1
-$(pi-objs): objtool-args	= $(if $(delay-objtool),,$(objtool-args-y)) --noabs
+$(pi-objs): objtool-args	= $(if $(delay-objtool),--dry-run,$(objtool-args-y)) --noabs
 
 #
 # Confine the startup code by prefixing all symbols with __pi_ (for position

scripts/Makefile.lib

···
 
 objtool := $(objtree)/tools/objtool/objtool
 
-objtool-args-$(CONFIG_KLP_BUILD)			+= --checksum
 objtool-args-$(CONFIG_HAVE_JUMP_LABEL_HACK)		+= --hacks=jump_label
 objtool-args-$(CONFIG_HAVE_NOINSTR_HACK)		+= --hacks=noinstr
 objtool-args-$(CONFIG_MITIGATION_CALL_DEPTH_TRACKING)	+= --hacks=skylake

scripts/livepatch/klp-build

···
 
 build_kernel() {
 	local log="$TMP_DIR/build.log"
+	local objtool_args=()
 	local cmd=()
+
+	objtool_args=("--checksum")
 
 	cmd=("make")
 
···
 	cmd+=("$VERBOSE")
 	cmd+=("-j$JOBS")
 	cmd+=("KCFLAGS=-ffunction-sections -fdata-sections")
+	cmd+=("OBJTOOL_ARGS=${objtool_args[*]}")
 	cmd+=("vmlinux")
 	cmd+=("modules")