busybox: compile with LTO enabled

In the default configuration on MIPS, it reduces the .ipk size
from 214k to 207k

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/utils/busybox/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=busybox
 PKG_VERSION:=1.28.4
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 PKG_FLAGS:=essential
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
@@ -20,7 +20,6 @@ PKG_HASH:=e3c14a3699dc7e82fed397392957afc78e37bdf25398ac38ead6e84621b2ae6a
 PKG_BUILD_DEPENDS:=BUSYBOX_USE_LIBRPC:librpc BUSYBOX_CONFIG_PAM:libpam
 PKG_BUILD_PARALLEL:=1
 PKG_CHECK_FORMAT_SECURITY:=0
-PKG_INSTALL:=1
 
 #Busybox use it's own PIE config flag and LDFLAGS are used with ld, not gcc.
 PKG_ASLR_PIE:=0
@@ -75,7 +74,10 @@ endef
 export KCONFIG_NOTIMESTAMP=1
 
 
+ifndef CONFIG_USE_MUSL
 LDLIBS:=m crypt
+endif
+
 LDLIBS += $(call BUSYBOX_IF_ENABLED,PAM,pam pam_misc pthread)
 ifdef CONFIG_BUSYBOX_USE_LIBRPC
   LDLIBS += rpc
@@ -84,24 +86,32 @@ ifeq ($(CONFIG_USE_GLIBC),y)
   LDLIBS += $(call BUSYBOX_IF_ENABLED,NSLOOKUP_OPENWRT,resolv)
 endif
 
+TARGET_CFLAGS += -flto
+TARGET_LDFLAGS += -flto=jobserver -fuse-linker-plugin
+
 MAKE_VARS :=
 MAKE_FLAGS += \
 	EXTRA_CFLAGS="$(TARGET_CFLAGS) $(TARGET_CPPFLAGS)" \
 	EXTRA_LDFLAGS="$(TARGET_LDFLAGS)" \
 	LDLIBS="$(LDLIBS)" \
+	LD="$(TARGET_CC)" \
 	SKIP_STRIP=y
 ifneq ($(findstring c,$(OPENWRT_VERBOSE)),)
   MAKE_FLAGS += V=1
 endif
 
-MAKE_INSTALL_FLAGS += CONFIG_PREFIX="$(PKG_INSTALL_DIR)"
-
-
 define Build/Configure
 	grep 'CONFIG_BUSYBOX_$(BUSYBOX_SYM)' $(TOPDIR)/.config | sed -e "s,\\(# \)\\?CONFIG_BUSYBOX_$(BUSYBOX_SYM)_\\(.*\\),\\1CONFIG_\\2,g" > $(PKG_BUILD_DIR)/.config
 	yes 'n' | $(MAKE) -C $(PKG_BUILD_DIR) $(MAKE_FLAGS) oldconfig
 endef
 
+define Build/Compile
+	$(call Build/Compile/Default, \
+		CONFIG_PREFIX="$(PKG_INSTALL_DIR)" \
+		all install \
+	)
+endef
+
 define Package/busybox/install
 	$(INSTALL_DIR) $(1)/etc/init.d
 	$(CP) $(PKG_INSTALL_DIR)/* $(1)/

package/utils/busybox/patches/120-lto-jobserver.patch

@@ -0,0 +1,27 @@
+--- a/scripts/Kbuild.include
++++ b/scripts/Kbuild.include
+@@ -130,7 +130,7 @@ make-cmd = $(subst \#,\\\#,$(subst $$,$$
+ #
+ if_changed = $(if $(strip $(filter-out $(PHONY),$?)          \
+ 		$(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
+-	@set -e; \
++	+@set -e; \
+ 	$(echo-cmd) $(cmd_$(1)); \
+ 	echo 'cmd_$@ := $(make-cmd)' > $(@D)/.$(@F).cmd)
+ 
+@@ -139,7 +139,7 @@ if_changed = $(if $(strip $(filter-out $
+ if_changed_dep = $(if $(strip $(filter-out $(PHONY),$?)  \
+ 		$(filter-out FORCE $(wildcard $^),$^)    \
+ 	$(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),     \
+-	@set -e; \
++	+@set -e; \
+ 	$(echo-cmd) $(cmd_$(1)); \
+ 	scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(@D)/.$(@F).tmp; \
+ 	rm -f $(depfile); \
+@@ -150,5 +150,5 @@ if_changed_dep = $(if $(strip $(filter-o
+ # and if so will execute $(rule_foo)
+ if_changed_rule = $(if $(strip $(filter-out $(PHONY),$?)            \
+ 			$(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),\
+-			@set -e; \
++			+@set -e; \
+ 			$(rule_$(1)))