treewide: add support for "lto" in PKG_BUILD_FLAGS

This reduces open coding and allows to easily add a knob to enable
it treewide, where chosen packages can still opt-out via "no-lto".

Some packages used LTO, but not the linker plugin. This unifies 'em
all to attempt to produce better code.
Quoting man gcc(1):
"This improves the quality of optimization by exposing more code to the
link-time optimizer."

Also use -flto=auto instead of -flto=jobserver, as it's not guaranteed
that every buildsystem uses +$(MAKE) correctly.

Signed-off-by: Andre Heider <[email protected]>

include/package.mk

@@ -30,7 +30,7 @@ ifneq ($(strip $(PKG_USE_MIPS16)),1)
   PKG_BUILD_FLAGS+=no-mips16
 endif
 
-__unknown_flags=$(filter-out no-iremap no-mips16 gc-sections no-gc-sections,$(PKG_BUILD_FLAGS))
+__unknown_flags=$(filter-out no-iremap no-mips16 gc-sections no-gc-sections lto no-lto,$(PKG_BUILD_FLAGS))
 ifneq ($(__unknown_flags),)
   $(error unknown PKG_BUILD_FLAGS: $(__unknown_flags))
 endif
@@ -56,6 +56,11 @@ ifeq ($(call pkg_build_flag,gc-sections,0),1)
   TARGET_CXXFLAGS+= -ffunction-sections -fdata-sections
   TARGET_LDFLAGS+= -Wl,--gc-sections
 endif
+ifeq ($(call pkg_build_flag,lto,0),1)
+  TARGET_CFLAGS+= -flto=auto -fno-fat-lto-objects
+  TARGET_CXXFLAGS+= -flto=auto -fno-fat-lto-objects
+  TARGET_LDFLAGS+= -flto=auto -fuse-linker-plugin
+endif
 
 include $(INCLUDE_DIR)/hardening.mk
 include $(INCLUDE_DIR)/prereq.mk

package/libs/jansson/Makefile

@@ -19,6 +19,8 @@ PKG_LICENSE:=MIT
 PKG_LICENSE_FILES:=LICENSE
 PKG_CPE_ID:=cpe:/a:jansson_project:jansson
 
+PKG_BUILD_FLAGS:=lto
+
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
 
@@ -41,9 +43,6 @@ define Package/jansson/description
   Jansson is a C library for encoding, decoding and manipulating JSON data
 endef
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto
-
 define Package/jansson/install
 	$(INSTALL_DIR) $(1)/usr/lib
 	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libjansson*so.* $(1)/usr/lib/

package/libs/libevent2/Makefile

@@ -26,7 +26,7 @@ PKG_CONFIG_DEPENDS:= \
 	CONFIG_PACKAGE_libevent2-pthreads \
 	CONFIG_PACKAGE_libevent2-mbedtls
 
-PKG_BUILD_FLAGS:=gc-sections
+PKG_BUILD_FLAGS:=gc-sections lto
 
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
@@ -114,8 +114,8 @@ define Package/libevent2-pthreads/description
 	threading & locking.
 endef
 
-TARGET_CFLAGS += $(FPIC) -flto
-TARGET_LDFLAGS += -Wl,--as-needed -flto
+TARGET_CFLAGS += $(FPIC)
+TARGET_LDFLAGS += -Wl,--as-needed
 
 CMAKE_OPTIONS += \
 	-DEVENT__DISABLE_BENCHMARK:BOOL=ON \

package/libs/libnftnl/Makefile

@@ -22,6 +22,7 @@ PKG_LICENSE_FILES:=COPYING
 
 PKG_INSTALL:=1
 PKG_BUILD_PARALLEL:=1
+PKG_BUILD_FLAGS:=lto
 
 include $(INCLUDE_DIR)/package.mk
 
@@ -41,8 +42,7 @@ define Package/libnftnl/description
  programming interface (API) to the in-kernel nf_tables subsystem.
 endef
 
-TARGET_CFLAGS += $(FPIC) -flto
-TARGET_LDFLAGS += -flto
+TARGET_CFLAGS += $(FPIC)
 
 CONFIGURE_ARGS += \
 	--enable-static \

package/libs/wolfssl/Makefile

@@ -17,7 +17,7 @@ PKG_HASH:=b7ee150e49def77c765bc02aac92ddeb0bebefd4cb12aa263d8f95e405221fb8
 
 PKG_FIXUP:=libtool libtool-abiver
 PKG_INSTALL:=1
-PKG_BUILD_FLAGS:=no-mips16
+PKG_BUILD_FLAGS:=no-mips16 lto
 PKG_BUILD_PARALLEL:=1
 PKG_LICENSE:=GPL-2.0-or-later
 PKG_LICENSE_FILES:=LICENSING COPYING
@@ -118,12 +118,9 @@ endef
 TARGET_CFLAGS += \
 	$(FPIC) \
 	-fomit-frame-pointer \
-	-flto \
 	-DFP_MAX_BITS=8192 \
 	$(if $(CONFIG_WOLFSSL_ALT_NAMES),-DWOLFSSL_ALT_NAMES)
 
-TARGET_LDFLAGS += -flto
-
 # --enable-stunnel needed for OpenSSL API compatibility bits
 CONFIGURE_ARGS += \
 	--enable-reproducible-build \

package/network/config/firewall/Makefile

@@ -21,7 +21,7 @@ PKG_LICENSE:=ISC
 
 PKG_CONFIG_DEPENDS := CONFIG_IPV6
 
-PKG_BUILD_FLAGS:=gc-sections
+PKG_BUILD_FLAGS:=gc-sections lto
 
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
@@ -44,8 +44,6 @@ define Package/firewall/conffiles
 /etc/firewall.user
 endef
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto
 CMAKE_OPTIONS += $(if $(CONFIG_IPV6),,-DDISABLE_IPV6=1)
 
 define Package/firewall/install

package/network/config/netifd/Makefile

@@ -13,6 +13,8 @@ PKG_MAINTAINER:=Felix Fietkau <[email protected]>
 PKG_LICENSE:=GPL-2.0
 PKG_LICENSE_FILES:=
 
+PKG_BUILD_FLAGS:=lto
+
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
 
@@ -30,10 +32,7 @@ endef
 
 TARGET_CFLAGS += \
 	-I$(STAGING_DIR)/usr/include/libnl-tiny \
-	-I$(STAGING_DIR)/usr/include \
-	-flto
-
-TARGET_LDFLAGS += -flto -fuse-linker-plugin
+	-I$(STAGING_DIR)/usr/include
 
 CMAKE_OPTIONS += \
 	-DLIBNL_LIBS=-lnl-tiny \

package/network/config/swconfig/Makefile

@@ -13,6 +13,8 @@ PKG_RELEASE:=12
 PKG_MAINTAINER:=Felix Fietkau <[email protected]>
 PKG_LICENSE:=GPL-2.0
 
+PKG_BUILD_FLAGS:=lto
+
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/kernel.mk
 
@@ -23,9 +25,6 @@ define Package/swconfig
   TITLE:=Switch configuration utility
 endef
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto=jobserver
-
 TARGET_CPPFLAGS := \
 	-D_GNU_SOURCE \
 	-I$(STAGING_DIR)/usr/include/libnl-tiny \

package/network/services/dnsmasq/Makefile

@@ -24,6 +24,7 @@ PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(BUILD_VARIANT)/$(PKG_NAME)-$(PKG_UPSTR
 
 PKG_INSTALL:=1
 PKG_BUILD_PARALLEL:=1
+PKG_BUILD_FLAGS:=lto
 PKG_ASLR_PIE_REGULAR:=1
 PKG_CONFIG_DEPENDS:= CONFIG_PACKAGE_dnsmasq_$(BUILD_VARIANT)_dhcp \
 	CONFIG_PACKAGE_dnsmasq_$(BUILD_VARIANT)_dhcpv6 \
@@ -133,9 +134,6 @@ endef
 Package/dnsmasq-dhcpv6/conffiles = $(Package/dnsmasq/conffiles)
 Package/dnsmasq-full/conffiles = $(Package/dnsmasq/conffiles)
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto=jobserver
-
 COPTS = -DHAVE_UBUS -DHAVE_POLL_H \
 	$(if $(CONFIG_IPV6),,-DNO_IPV6)
 

package/network/services/dropbear/Makefile

@@ -23,7 +23,7 @@ PKG_CPE_ID:=cpe:/a:matt_johnston:dropbear_ssh_server
 
 PKG_BUILD_PARALLEL:=1
 PKG_ASLR_PIE_REGULAR:=1
-PKG_BUILD_FLAGS:=no-mips16 gc-sections
+PKG_BUILD_FLAGS:=no-mips16 gc-sections lto
 PKG_FIXUP:=autoreconf
 PKG_FLAGS:=nonshared
 
@@ -142,8 +142,7 @@ DB_OPT_CONFIG = \
 	DROPBEAR_SVR_AGENTFWD|CONFIG_DROPBEAR_AGENTFORWARD|1|0 \
 
 
-TARGET_CFLAGS += -DARGTYPE=3 -flto
-TARGET_LDFLAGS += -flto=jobserver
+TARGET_CFLAGS += -DARGTYPE=3
 
 db_opt_add     =echo '\#define $(1) $(2)' >> $(PKG_BUILD_DIR)/localoptions.h
 db_opt_replace =$(ESED) 's,^(\#define $(1)) .*$$$$,\1 $(2),g' $(PKG_BUILD_DIR)/sysoptions.h

package/network/services/hostapd/Makefile

@@ -32,7 +32,7 @@ PKG_CONFIG_DEPENDS:= \
 	CONFIG_DRIVER_11AX_SUPPORT \
 	CONFIG_WPA_ENABLE_WEP
 
-PKG_BUILD_FLAGS:=gc-sections
+PKG_BUILD_FLAGS:=gc-sections lto
 
 EAPOL_TEST_PROVIDERS:=eapol-test eapol-test-openssl eapol-test-wolfssl
 
@@ -587,8 +587,7 @@ TARGET_CPPFLAGS := \
 	-D_GNU_SOURCE \
 	$(if $(CONFIG_WPA_MSG_MIN_PRIORITY),-DCONFIG_MSG_MIN_PRIORITY=$(CONFIG_WPA_MSG_MIN_PRIORITY))
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto=jobserver -fuse-linker-plugin -lubox -lubus
+TARGET_LDFLAGS += -lubox -lubus
 
 ifdef CONFIG_PACKAGE_kmod-cfg80211
   TARGET_LDFLAGS += -lm -lnl-tiny

package/network/services/lldpd/Makefile

@@ -21,6 +21,7 @@ PKG_CPE_ID:=cpe:/a:lldpd_project:lldpd
 
 PKG_FIXUP:=autoreconf
 PKG_BUILD_PARALLEL:=1
+PKG_BUILD_FLAGS:=lto
 PKG_INSTALL:=1
 
 include $(INCLUDE_DIR)/package.mk
@@ -111,7 +112,6 @@ CONFIGURE_ARGS += \
 	$(if $(CONFIG_LLDPD_WITH_SNMP),--with-snmp,) \
 	$(if $(CONFIG_USE_GLIBC),,--without-libbsd)
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto -Wl,--gc-sections,--as-needed
+TARGET_LDFLAGS += -Wl,--gc-sections,--as-needed
 
 $(eval $(call BuildPackage,lldpd))

package/network/services/ppp/Makefile

@@ -26,7 +26,7 @@ PKG_VERSION:=$(PKG_RELEASE_VERSION).git-$(PKG_SOURCE_DATE)
 PKG_BUILD_DEPENDS:=libpcap
 
 PKG_ASLR_PIE_REGULAR:=1
-PKG_BUILD_FLAGS:=gc-sections
+PKG_BUILD_FLAGS:=gc-sections lto
 PKG_BUILD_PARALLEL:=1
 PKG_INSTALL:=1
 
@@ -193,9 +193,6 @@ $(call Build/Configure/Default,, \
 		$(PKG_BUILD_DIR)/pppd/plugins/pppoatm/linux/
 endef
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto -fuse-linker-plugin
-
 MAKE_FLAGS += COPTS="$(TARGET_CFLAGS)" \
 		PRECOMPILED_FILTER=1 \
 		STAGING_DIR="$(STAGING_DIR)"

package/network/services/ustp/Makefile

@@ -19,6 +19,8 @@ PKG_MIRROR_HASH:=0e96edc983cf437b95874e5715d743f30bb826d8757dc3771ff872ab9cf18f3
 PKG_MAINTAINER:=Felix Fietkau <[email protected]>
 PKG_LICENSE:=GPL-2.0
 
+PKG_BUILD_FLAGS:=lto
+
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
 
@@ -29,8 +31,7 @@ define Package/ustp
   DEPENDS:=+libubox +libubus
 endef
 
-TARGET_CFLAGS += -I$(STAGING_DIR)/usr/include -flto
-TARGET_LDFLAGS += -flto -fuse-linker-plugin
+TARGET_CFLAGS += -I$(STAGING_DIR)/usr/include
 
 define Package/ustp/install
 	$(INSTALL_DIR) $(1)/sbin $(1)/etc/init.d

package/network/utils/iproute2/Makefile

@@ -19,7 +19,7 @@ PKG_BUILD_DEPENDS:=iptables
 PKG_LICENSE:=GPL-2.0
 PKG_CPE_ID:=cpe:/a:iproute2_project:iproute2
 
-PKG_BUILD_FLAGS:=gc-sections
+PKG_BUILD_FLAGS:=gc-sections lto
 
 include $(INCLUDE_DIR)/kernel.mk
 include $(INCLUDE_DIR)/package.mk
@@ -173,7 +173,6 @@ define Build/Configure
 		> $(PKG_BUILD_DIR)/include/SNAPSHOT.h
 endef
 
-TARGET_CFLAGS += -flto
 TARGET_LDFLAGS += -Wl,--as-needed
 TARGET_CPPFLAGS += -I$(STAGING_DIR)/usr/include/libnl-tiny
 

package/network/utils/iw/Makefile

@@ -18,7 +18,7 @@ PKG_HASH:=f167bbe947dd53bb9ebc0c1dcef5db6ad73ac1d6084f2c6f9376c5c360cc4d4e
 PKG_MAINTAINER:=Felix Fietkau <[email protected]>
 PKG_LICENSE:=GPL-2.0
 
-PKG_BUILD_FLAGS:=gc-sections
+PKG_BUILD_FLAGS:=gc-sections lto
 
 include $(INCLUDE_DIR)/package.mk
 
@@ -48,8 +48,7 @@ TARGET_CPPFLAGS:= \
 	-I$(STAGING_DIR)/usr/include/libnl-tiny \
 	$(TARGET_CPPFLAGS) \
 	-DCONFIG_LIBNL20 \
-	-D_GNU_SOURCE \
-	-flto
+	-D_GNU_SOURCE
 
 ifeq ($(BUILD_VARIANT),full)
   TARGET_CPPFLAGS += -DIW_FULL
@@ -58,7 +57,7 @@ endif
 
 MAKE_FLAGS += \
 	CFLAGS="$(TARGET_CPPFLAGS) $(TARGET_CFLAGS)" \
-	LDFLAGS="$(TARGET_LDFLAGS) -flto" \
+	LDFLAGS="$(TARGET_LDFLAGS)" \
 	NL1FOUND="" NL2FOUND=Y \
 	NLLIBNAME="libnl-tiny" \
 	LIBS="-lm -lnl-tiny" \

package/network/utils/nftables/Makefile

@@ -20,6 +20,8 @@ PKG_LICENSE_FILES:=COPYING
 PKG_FIXUP:=autoreconf
 PKG_INSTALL:=1
 
+PKG_BUILD_FLAGS:=lto
+
 include $(INCLUDE_DIR)/package.mk
 
 DISABLE_NLS:=
@@ -60,9 +62,6 @@ ifeq ($(BUILD_VARIANT),json)
   CONFIGURE_ARGS += --with-json
 endif
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto
-
 define Build/InstallDev
 	$(INSTALL_DIR) $(1)/usr/lib $(1)/usr/include
 	$(CP) $(PKG_INSTALL_DIR)/usr/lib/*.so* $(1)/usr/lib/

package/system/mtd/Makefile

@@ -18,6 +18,7 @@ PKG_LICENSE:=GPL-2.0+
 PKG_LICENSE_FILES:=
 
 PKG_FLAGS:=nonshared
+PKG_BUILD_FLAGS:=lto
 
 include $(INCLUDE_DIR)/package.mk
 
@@ -36,8 +37,7 @@ endef
 target=$(firstword $(subst -, ,$(BOARD)))
 
 MAKE_FLAGS += TARGET="$(target)"
-TARGET_CFLAGS += -Dtarget_$(target)=1 -Wall -flto
-TARGET_LDFLAGS += -flto=jobserver
+TARGET_CFLAGS += -Dtarget_$(target)=1 -Wall
 
 ifdef CONFIG_MTD_REDBOOT_PARTS
   MAKE_FLAGS += FIS_SUPPORT=1

package/system/procd/Makefile

@@ -22,6 +22,7 @@ PKG_LICENSE_FILES:=
 
 PKG_MAINTAINER:=John Crispin <[email protected]>
 
+PKG_BUILD_FLAGS:=lto
 PKG_ASLR_PIE_REGULAR:=1
 PKG_CONFIG_DEPENDS:= \
 	CONFIG_TARGET_INIT_PATH CONFIG_KERNEL_SECCOMP CONFIG_PROCD_SHOW_BOOT \
@@ -36,9 +37,6 @@ endif
 
 CMAKE_OPTIONS += -DEARLY_PATH="$(TARGET_INIT_PATH)"
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto
-
 define Package/procd/Default
   SECTION:=base
   CATEGORY:=Base system

package/system/ubus/Makefile

@@ -15,6 +15,7 @@ PKG_LICENSE:=LGPL-2.1
 PKG_LICENSE_FILES:=
 PKG_MAINTAINER:=Felix Fietkau <[email protected]>
 
+PKG_BUILD_FLAGS:=lto
 PKG_ASLR_PIE_REGULAR:=1
 
 include $(INCLUDE_DIR)/package.mk
@@ -50,8 +51,7 @@ define Package/libubus-lua
   TITLE:=Lua binding for the OpenWrt RPC client
 endef
 
-TARGET_CFLAGS += -I$(STAGING_DIR)/usr/include -flto
-TARGET_LDFLAGS += -flto
+TARGET_CFLAGS += -I$(STAGING_DIR)/usr/include
 
 CMAKE_OPTIONS += \
 	-DLUAPATH=/usr/lib/lua \

package/system/usign/Makefile

@@ -10,7 +10,7 @@ PKG_SOURCE_VERSION:=f1f65026a94137c91b5466b149ef3ea3f20091e9
 PKG_MIRROR_HASH:=3f6569a5e63fdfd032976ac0f79d736d3935101ac1b97fb370514b013c5e6bb6
 CMAKE_INSTALL:=1
 PKG_CHECK_FORMAT_SECURITY:=1
-PKG_BUILD_FLAGS:=no-mips16
+PKG_BUILD_FLAGS:=no-mips16 lto
 
 PKG_LICENSE:=ISC
 PKG_LICENSE_FILES:=
@@ -30,9 +30,6 @@ define Package/usign
   TITLE:=OpenWrt signature verification utility
 endef
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto=jobserver
-
 CMAKE_OPTIONS += \
 	-DUSE_LIBUBOX=on
 

package/utils/busybox/Makefile

@@ -16,6 +16,7 @@ PKG_HASH:=542750c8af7cb2630e201780b4f99f3dcceeb06f505b479ec68241c1e6af61a5
 
 PKG_BUILD_DEPENDS:=BUSYBOX_CONFIG_PAM:libpam
 PKG_BUILD_PARALLEL:=1
+PKG_BUILD_FLAGS:=lto
 PKG_CHECK_FORMAT_SECURITY:=0
 
 PKG_LICENSE:=GPL-2.0
@@ -103,9 +104,6 @@ ifeq ($(BUILD_VARIANT),selinux)
   LDLIBS += selinux sepol
 endif
 
-TARGET_CFLAGS += -flto
-TARGET_LDFLAGS += -flto=jobserver -fuse-linker-plugin
-
 MAKE_VARS :=
 MAKE_FLAGS += \
 	EXTRA_CFLAGS="$(TARGET_CFLAGS) $(TARGET_CPPFLAGS)" \

package/utils/e2fsprogs/Makefile

@@ -23,7 +23,7 @@ PKG_BUILD_DEPENDS:=util-linux e2fsprogs/host
 PKG_INSTALL:=1
 
 PKG_BUILD_PARALLEL:=1
-PKG_BUILD_FLAGS:=gc-sections
+PKG_BUILD_FLAGS:=gc-sections lto
 
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/host-build.mk
@@ -143,9 +143,7 @@ $(call Package/e2fsprogs)
   DEPENDS:= +e2fsprogs
 endef
 
-TARGET_CFLAGS += $(FPIC) -flto
-
-TARGET_LDFLAGS += -flto
+TARGET_CFLAGS += $(FPIC)
 
 CONFIGURE_ARGS += \
 	--disable-testio-debug \