treewide: add support for "gc-sections" 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-gc-sections".

Note: libnl, mbedtls and opkg only used the CFLAGS part without the
LDFLAGS counterpart. That doesn't help at all if the goal is to produce
smaller binaries. I consider that an accident, and this fixes it.

Note: there are also packages using only the LDFLAGS part. I didn't
touch those, as gc might have been disabled via CFLAGS intentionally.

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=$(filter-out no-iremap no-mips16,$(PKG_BUILD_FLAGS))
+__unknown_flags=$(filter-out no-iremap no-mips16 gc-sections no-gc-sections,$(PKG_BUILD_FLAGS))
 ifneq ($(__unknown_flags),)
   $(error unknown PKG_BUILD_FLAGS: $(__unknown_flags))
 endif
@@ -51,6 +51,11 @@ ifdef CONFIG_USE_MIPS16
     TARGET_CXXFLAGS += -mips16 -minterlink-mips16
   endif
 endif
+ifeq ($(call pkg_build_flag,gc-sections,0),1)
+  TARGET_CFLAGS+= -ffunction-sections -fdata-sections
+  TARGET_CXXFLAGS+= -ffunction-sections -fdata-sections
+  TARGET_LDFLAGS+= -Wl,--gc-sections
+endif
 
 include $(INCLUDE_DIR)/hardening.mk
 include $(INCLUDE_DIR)/prereq.mk

package/boot/kexec-tools/Makefile

@@ -17,6 +17,8 @@ PKG_HASH:=7fe36a064101cd5c515e41b2be393dce3ca88adce59d6ee668e0af7c0c4570cd
 
 PKG_CONFIG_DEPENDS := CONFIG_KEXEC_ZLIB CONFIG_KEXEC_LZMA
 
+PKG_BUILD_FLAGS:=gc-sections
+
 include $(INCLUDE_DIR)/package.mk
 
 define Package/kexec-tools/Default
@@ -82,9 +84,6 @@ CONFIGURE_ARGS = \
 		$(if $(CONFIG_KEXEC_LZMA),--with,--without)-lzma \
 		TARGET_LD="$(TARGET_CROSS)ld"
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections
-TARGET_LDFLAGS += -Wl,--gc-sections
-
 CONFIGURE_VARS += \
 	BUILD_CC="$(HOSTCC)" \
 	TARGET_CC="$(TARGET_CC)"

package/libs/libevent2/Makefile

@@ -26,6 +26,8 @@ PKG_CONFIG_DEPENDS:= \
 	CONFIG_PACKAGE_libevent2-pthreads \
 	CONFIG_PACKAGE_libevent2-mbedtls
 
+PKG_BUILD_FLAGS:=gc-sections
+
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
 
@@ -112,8 +114,8 @@ define Package/libevent2-pthreads/description
 	threading & locking.
 endef
 
-TARGET_CFLAGS += $(FPIC) -ffunction-sections -fdata-sections -flto
-TARGET_LDFLAGS += -Wl,--gc-sections,--as-needed -flto
+TARGET_CFLAGS += $(FPIC) -flto
+TARGET_LDFLAGS += -Wl,--as-needed -flto
 
 CMAKE_OPTIONS += \
 	-DEVENT__DISABLE_BENCHMARK:BOOL=ON \

package/libs/libnl/Makefile

@@ -20,6 +20,8 @@ PKG_CPE_ID:=cpe:/a:libnl_project:libnl
 PKG_INSTALL:=1
 PKG_FIXUP:=autoreconf
 
+PKG_BUILD_FLAGS:=gc-sections
+
 include $(INCLUDE_DIR)/package.mk
 
 define Package/libnl/default
@@ -80,7 +82,7 @@ define Package/libnl/description
  message construction and parsing, object caching system, etc.
 endef
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections $(FPIC)
+TARGET_CFLAGS += $(FPIC)
 
 CONFIGURE_ARGS += \
 	--disable-debug

package/libs/mbedtls/Makefile

@@ -10,7 +10,7 @@ include $(TOPDIR)/rules.mk
 PKG_NAME:=mbedtls
 PKG_VERSION:=2.28.2
 PKG_RELEASE:=2
-PKG_BUILD_FLAGS:=no-mips16
+PKG_BUILD_FLAGS:=no-mips16 gc-sections
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://codeload.github.com/ARMmbed/mbedtls/tar.gz/v$(PKG_VERSION)?
@@ -121,7 +121,6 @@ This package contains mbedtls helper programs for private key and
 CSR generation (gen_key, cert_req)
 endef
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections
 TARGET_CFLAGS := $(filter-out -O%,$(TARGET_CFLAGS))
 
 CMAKE_OPTIONS += \

package/libs/openssl/Makefile

@@ -10,7 +10,7 @@ include $(TOPDIR)/rules.mk
 PKG_NAME:=openssl
 PKG_VERSION:=3.0.8
 PKG_RELEASE:=4
-PKG_BUILD_FLAGS:=no-mips16
+PKG_BUILD_FLAGS:=no-mips16 gc-sections
 
 PKG_BUILD_PARALLEL:=1
 
@@ -339,8 +339,7 @@ define Build/Configure
 	)
 endef
 
-TARGET_CFLAGS += $(FPIC) -ffunction-sections -fdata-sections
-TARGET_LDFLAGS += -Wl,--gc-sections
+TARGET_CFLAGS += $(FPIC)
 
 define Build/Compile
 	+$(MAKE) $(PKG_JOBS) -C $(PKG_BUILD_DIR) \

package/network/config/firewall/Makefile

@@ -21,6 +21,8 @@ PKG_LICENSE:=ISC
 
 PKG_CONFIG_DEPENDS := CONFIG_IPV6
 
+PKG_BUILD_FLAGS:=gc-sections
+
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
 
@@ -42,8 +44,8 @@ define Package/firewall/conffiles
 /etc/firewall.user
 endef
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections -flto
-TARGET_LDFLAGS += -Wl,--gc-sections -flto
+TARGET_CFLAGS += -flto
+TARGET_LDFLAGS += -flto
 CMAKE_OPTIONS += $(if $(CONFIG_IPV6),,-DDISABLE_IPV6=1)
 
 define Package/firewall/install

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
+PKG_BUILD_FLAGS:=no-mips16 gc-sections
 PKG_FIXUP:=autoreconf
 PKG_FLAGS:=nonshared
 
@@ -142,8 +142,8 @@ DB_OPT_CONFIG = \
 	DROPBEAR_SVR_AGENTFWD|CONFIG_DROPBEAR_AGENTFORWARD|1|0 \
 
 
-TARGET_CFLAGS += -DARGTYPE=3 -ffunction-sections -fdata-sections -flto
-TARGET_LDFLAGS += -Wl,--gc-sections -flto=jobserver
+TARGET_CFLAGS += -DARGTYPE=3 -flto
+TARGET_LDFLAGS += -flto=jobserver
 
 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

@@ -32,6 +32,8 @@ PKG_CONFIG_DEPENDS:= \
 	CONFIG_DRIVER_11AX_SUPPORT \
 	CONFIG_WPA_ENABLE_WEP
 
+PKG_BUILD_FLAGS:=gc-sections
+
 EAPOL_TEST_PROVIDERS:=eapol-test eapol-test-openssl eapol-test-wolfssl
 
 SUPPLICANT_PROVIDERS:=
@@ -585,8 +587,8 @@ TARGET_CPPFLAGS := \
 	-D_GNU_SOURCE \
 	$(if $(CONFIG_WPA_MSG_MIN_PRIORITY),-DCONFIG_MSG_MIN_PRIORITY=$(CONFIG_WPA_MSG_MIN_PRIORITY))
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections -flto
-TARGET_LDFLAGS += -Wl,--gc-sections -flto=jobserver -fuse-linker-plugin -lubox -lubus
+TARGET_CFLAGS += -flto
+TARGET_LDFLAGS += -flto=jobserver -fuse-linker-plugin -lubox -lubus
 
 ifdef CONFIG_PACKAGE_kmod-cfg80211
   TARGET_LDFLAGS += -lm -lnl-tiny

package/network/services/ppp/Makefile

@@ -26,6 +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_PARALLEL:=1
 PKG_INSTALL:=1
 
@@ -192,8 +193,8 @@ $(call Build/Configure/Default,, \
 		$(PKG_BUILD_DIR)/pppd/plugins/pppoatm/linux/
 endef
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections -flto
-TARGET_LDFLAGS += -Wl,--gc-sections -flto -fuse-linker-plugin
+TARGET_CFLAGS += -flto
+TARGET_LDFLAGS += -flto -fuse-linker-plugin
 
 MAKE_FLAGS += COPTS="$(TARGET_CFLAGS)" \
 		PRECOMPILED_FILTER=1 \

package/network/utils/iproute2/Makefile

@@ -19,6 +19,8 @@ PKG_BUILD_DEPENDS:=iptables
 PKG_LICENSE:=GPL-2.0
 PKG_CPE_ID:=cpe:/a:iproute2_project:iproute2
 
+PKG_BUILD_FLAGS:=gc-sections
+
 include $(INCLUDE_DIR)/kernel.mk
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/nls.mk
@@ -171,8 +173,8 @@ define Build/Configure
 		> $(PKG_BUILD_DIR)/include/SNAPSHOT.h
 endef
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections -flto
-TARGET_LDFLAGS += -Wl,--gc-sections -Wl,--as-needed
+TARGET_CFLAGS += -flto
+TARGET_LDFLAGS += -Wl,--as-needed
 TARGET_CPPFLAGS += -I$(STAGING_DIR)/usr/include/libnl-tiny
 
 MAKE_FLAGS += \

package/network/utils/iptables/Makefile

@@ -20,6 +20,7 @@ PKG_FIXUP:=autoreconf
 PKG_FLAGS:=nonshared
 
 PKG_INSTALL:=1
+PKG_BUILD_FLAGS:=gc-sections
 PKG_BUILD_PARALLEL:=1
 PKG_LICENSE:=GPL-2.0
 PKG_CPE_ID:=cpe:/a:netfilter_core_team:iptables
@@ -591,12 +592,8 @@ TARGET_CPPFLAGS := \
 TARGET_CFLAGS += \
 	-I$(PKG_BUILD_DIR)/include \
 	-I$(LINUX_DIR)/user_headers/include \
-	-ffunction-sections -fdata-sections \
 	-DNO_LEGACY
 
-TARGET_LDFLAGS += \
-	-Wl,--gc-sections
-
 CONFIGURE_ARGS += \
 	--enable-shared \
 	--enable-static \

package/network/utils/iw/Makefile

@@ -18,6 +18,8 @@ PKG_HASH:=f167bbe947dd53bb9ebc0c1dcef5db6ad73ac1d6084f2c6f9376c5c360cc4d4e
 PKG_MAINTAINER:=Felix Fietkau <[email protected]>
 PKG_LICENSE:=GPL-2.0
 
+PKG_BUILD_FLAGS:=gc-sections
+
 include $(INCLUDE_DIR)/package.mk
 
 define Package/iw
@@ -55,8 +57,8 @@ ifeq ($(BUILD_VARIANT),full)
 endif
 
 MAKE_FLAGS += \
-	CFLAGS="$(TARGET_CPPFLAGS) $(TARGET_CFLAGS) -ffunction-sections -fdata-sections" \
-	LDFLAGS="$(TARGET_LDFLAGS) -Wl,--gc-sections -flto" \
+	CFLAGS="$(TARGET_CPPFLAGS) $(TARGET_CFLAGS)" \
+	LDFLAGS="$(TARGET_LDFLAGS) -flto" \
 	NL1FOUND="" NL2FOUND=Y \
 	NLLIBNAME="libnl-tiny" \
 	LIBS="-lm -lnl-tiny" \

package/network/utils/tcpdump/Makefile

@@ -20,6 +20,7 @@ PKG_LICENSE:=BSD-3-Clause
 PKG_CPE_ID:=cpe:/a:tcpdump:tcpdump
 
 PKG_INSTALL:=1
+PKG_BUILD_FLAGS:=gc-sections
 PKG_BUILD_PARALLEL:=1
 
 include $(INCLUDE_DIR)/package.mk
@@ -48,9 +49,6 @@ CONFIGURE_ARGS += \
 	--without-crypto \
 	$(call autoconf_bool,CONFIG_IPV6,ipv6)
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections
-TARGET_LDFLAGS += -Wl,--gc-sections
-
 ifeq ($(BUILD_VARIANT),mini)
   TARGET_CFLAGS += -DTCPDUMP_MINI
   CONFIGURE_ARGS += --disable-smb

package/network/utils/umbim/Makefile

@@ -14,6 +14,7 @@ PKG_LICENSE:=GPL-2.0
 PKG_LICENSE_FILES:=
 
 PKG_FLAGS:=nonshared
+PKG_BUILD_FLAGS:=gc-sections
 
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
@@ -32,9 +33,7 @@ define Package/umbim/description
 endef
 
 TARGET_CFLAGS += \
-	-I$(STAGING_DIR)/usr/include -ffunction-sections -fdata-sections
-
-TARGET_LDFLAGS += -Wl,--gc-sections
+	-I$(STAGING_DIR)/usr/include
 
 define Package/umbim/install
 	$(INSTALL_DIR) $(1)/sbin

package/network/utils/uqmi/Makefile

@@ -14,6 +14,7 @@ PKG_LICENSE:=GPL-2.0
 PKG_LICENSE_FILES:=
 
 PKG_FLAGS:=nonshared
+PKG_BUILD_FLAGS:=gc-sections
 
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/cmake.mk
@@ -33,13 +34,9 @@ endef
 
 TARGET_CFLAGS += \
 	-I$(STAGING_DIR)/usr/include \
-	-ffunction-sections \
-	-fdata-sections \
 	-Wno-error=dangling-pointer \
 	-Wno-error=maybe-uninitialized
 
-TARGET_LDFLAGS += -Wl,--gc-sections
-
 CMAKE_OPTIONS += \
 	-DDEBUG=1
 

package/system/opkg/Makefile

@@ -28,6 +28,8 @@ PKG_CONFIG_DEPENDS += \
 
 HOST_BUILD_DEPENDS:=libubox/host
 
+PKG_BUILD_FLAGS:=gc-sections
+
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/host-build.mk
 include $(INCLUDE_DIR)/cmake.mk
@@ -57,7 +59,6 @@ define Package/opkg/conffiles
 /etc/opkg/customfeeds.conf
 endef
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections
 EXTRA_CFLAGS += $(TARGET_CPPFLAGS)
 
 CMAKE_OPTIONS += \

package/utils/e2fsprogs/Makefile

@@ -23,6 +23,7 @@ PKG_BUILD_DEPENDS:=util-linux e2fsprogs/host
 PKG_INSTALL:=1
 
 PKG_BUILD_PARALLEL:=1
+PKG_BUILD_FLAGS:=gc-sections
 
 include $(INCLUDE_DIR)/package.mk
 include $(INCLUDE_DIR)/host-build.mk
@@ -142,7 +143,7 @@ $(call Package/e2fsprogs)
   DEPENDS:= +e2fsprogs
 endef
 
-TARGET_CFLAGS += $(FPIC) -ffunction-sections -fdata-sections -flto
+TARGET_CFLAGS += $(FPIC) -flto
 
 TARGET_LDFLAGS += -flto
 
@@ -171,7 +172,6 @@ define Build/Compile
 		V=$(if $(findstring c,$(OPENWRT_VERBOSE)),1,) \
 		subst
 	+$(MAKE) $(PKG_JOBS) -C $(PKG_BUILD_DIR) \
-		LDFLAGS=-Wl,--gc-sections \
 		BUILDCC="$(HOSTCC)" \
 		DESTDIR="$(PKG_INSTALL_DIR)" \
 		ELF_OTHER_LIBS="$(TARGET_LDFLAGS) -luuid" \

package/utils/mdadm/Makefile

@@ -19,6 +19,7 @@ PKG_MAINTAINER:=Felix Fietkau <[email protected]>
 PKG_CPE_ID:=cpe:/a:mdadm_project:mdadm
 
 PKG_BUILD_PARALLEL:=1
+PKG_BUILD_FLAGS:=gc-sections
 
 include $(INCLUDE_DIR)/package.mk
 
@@ -43,7 +44,6 @@ define Package/mdadm/conffiles
 endef
 
 TARGET_CFLAGS += \
-	-ffunction-sections -fdata-sections \
 	-DHAVE_STDINT_H -DNO_COROSYNC -DNO_DLM -DUSE_PTHREADS \
 	-DCONFFILE='\"/var/etc/mdadm.conf\"' \
 	-DMAP_DIR='\"/var/run/mdadm\"' \
@@ -53,8 +53,6 @@ TARGET_CFLAGS += \
 
 TARGET_CXFLAGS = -DNO_LIBUDEV
 
-TARGET_LDFLAGS += -Wl,--gc-sections
-
 MAKE_FLAGS += \
 		CHECK_RUN_DIR=0 \
 		CXFLAGS="$(TARGET_CXFLAGS)"

package/utils/mtd-utils/Makefile

@@ -19,6 +19,7 @@ PKG_INSTALL:=1
 PKG_FIXUP:=autoreconf
 
 PKG_FLAGS:=nonshared
+PKG_BUILD_FLAGS:=gc-sections
 
 PKG_BUILD_DEPENDS:=util-linux
 
@@ -64,9 +65,6 @@ CONFIGURE_ARGS += \
 	--without-zstd \
 	--without-lzo
 
-TARGET_CFLAGS += -ffunction-sections -fdata-sections
-TARGET_LDFLAGS += -Wl,--gc-sections
-
 define Package/ubi-utils/install
 	$(INSTALL_DIR) $(1)/usr/sbin
 	$(INSTALL_BIN) \