From 0186d5207660fdc7d341f2d312d1f13c91f27854 Mon Sep 17 00:00:00 2001
From: coolsnowwolf <coolsnowwolf@gmail.com>
Date: Wed, 29 May 2024 10:35:11 +0800
Subject: [PATCH] build: introduce PKG_BUILD_FLAGS

---
 config/Config-build.in | 15 +++++++++++++
 include/package.mk     | 49 +++++++++++++++++++++++++++++++++++-------
 2 files changed, 56 insertions(+), 8 deletions(-)

diff --git a/config/Config-build.in b/config/Config-build.in
index c2303637c..49f40bb00 100644
--- a/config/Config-build.in
+++ b/config/Config-build.in
@@ -152,6 +152,21 @@ menu "Global build settings"
 		default n
 		help
 		  Adds -g3 to the CFLAGS.
+		  
+	config USE_GC_SECTIONS
+		bool
+		prompt "Dead code and data elimination for all packages (EXPERIMENTAL)"
+		help
+		  Places functions and data items into its own sections to use the linker's
+		  garbage collection capabilites.
+		  Packages can choose to opt-out via setting PKG_BUILD_FLAGS:=no-gc-sections
+
+	config USE_LTO
+		bool
+		prompt "Use the link-time optimizer for all packages (EXPERIMENTAL)"
+		help
+		  Adds LTO flags to the CFLAGS and LDFLAGS.
+		  Packages can choose to opt-out via setting PKG_BUILD_FLAGS:=no-lto
 
 	config IPV6
 		def_bool y
diff --git a/include/package.mk b/include/package.mk
index 368bf0d7c..75aa8aefe 100644
--- a/include/package.mk
+++ b/include/package.mk
@@ -11,8 +11,6 @@ include $(INCLUDE_DIR)/download.mk
 PKG_BUILD_DIR ?= $(BUILD_DIR)/$(if $(BUILD_VARIANT),$(PKG_NAME)-$(BUILD_VARIANT)/)$(PKG_NAME)$(if $(PKG_VERSION),-$(PKG_VERSION))
 PKG_INSTALL_DIR ?= $(PKG_BUILD_DIR)/ipkg-install
 PKG_BUILD_PARALLEL ?=
-PKG_USE_MIPS16 ?= 1
-PKG_IREMAP ?= 1
 PKG_SKIP_DOWNLOAD=$(USE_SOURCE_DIR)$(USE_GIT_TREE)$(USE_GIT_SRC_CHECKOUT)
 
 MAKE_J:=$(if $(MAKE_JOBSERVER),$(MAKE_JOBSERVER) $(if $(filter 3.% 4.0 4.1,$(MAKE_VERSION)),-j))
@@ -24,17 +22,52 @@ PKG_JOBS?=-j1
 else
 PKG_JOBS?=$(if $(PKG_BUILD_PARALLEL),$(MAKE_J),-j1)
 endif
-ifdef CONFIG_USE_MIPS16
-  ifeq ($(strip $(PKG_USE_MIPS16)),1)
-    TARGET_ASFLAGS_DEFAULT = $(filter-out -mips16 -minterlink-mips16,$(TARGET_CFLAGS))
-    TARGET_CFLAGS += -mips16 -minterlink-mips16
-  endif
+
+PKG_BUILD_FLAGS?=
+# TODO remove this when all packages moved to PKG_BUILD_FLAGS=no-mips16
+PKG_USE_MIPS16?=1
+ifneq ($(strip $(PKG_USE_MIPS16)),1)
+  PKG_BUILD_FLAGS+=no-mips16
 endif
-ifeq ($(strip $(PKG_IREMAP)),1)
+
+__unknown_flags=$(filter-out no-iremap no-mips16 gc-sections no-gc-sections lto no-lto no-mold,$(PKG_BUILD_FLAGS))
+ifneq ($(__unknown_flags),)
+  $(error unknown PKG_BUILD_FLAGS: $(__unknown_flags))
+endif
+
+# $1=flagname, $2=default (0/1)
+define pkg_build_flag
+$(if $(filter no-$(1),$(PKG_BUILD_FLAGS)),0,$(if $(filter $(1),$(PKG_BUILD_FLAGS)),1,$(2)))
+endef
+
+ifeq ($(call pkg_build_flag,iremap,1),1)
   IREMAP_CFLAGS = $(call iremap,$(PKG_BUILD_DIR),$(notdir $(PKG_BUILD_DIR)))
   TARGET_CFLAGS += $(IREMAP_CFLAGS)
 endif
 
+ifdef CONFIG_USE_MIPS16
+  ifeq ($(call pkg_build_flag,mips16,1),1)
+    TARGET_ASFLAGS_DEFAULT = $(filter-out -mips16 -minterlink-mips16,$(TARGET_CFLAGS))
+    TARGET_CFLAGS += -mips16 -minterlink-mips16
+    TARGET_CXXFLAGS += -mips16 -minterlink-mips16
+  endif
+endif
+ifeq ($(call pkg_build_flag,gc-sections,$(if $(CONFIG_USE_GC_SECTIONS),1,0)),1)
+  TARGET_CFLAGS+= -ffunction-sections -fdata-sections
+  TARGET_CXXFLAGS+= -ffunction-sections -fdata-sections
+  TARGET_LDFLAGS+= -Wl,--gc-sections
+endif
+ifeq ($(call pkg_build_flag,lto,$(if $(CONFIG_USE_LTO),1,0)),1)
+  TARGET_CFLAGS+= -flto=auto -fno-fat-lto-objects
+  TARGET_CXXFLAGS+= -flto=auto -fno-fat-lto-objects
+  TARGET_LDFLAGS+= -flto=auto -fuse-linker-plugin
+endif
+ifdef CONFIG_USE_MOLD
+  ifeq ($(call pkg_build_flag,mold,1),1)
+    TARGET_LINKER:=mold
+  endif
+endif
+
 include $(INCLUDE_DIR)/hardening.mk
 include $(INCLUDE_DIR)/prereq.mk
 include $(INCLUDE_DIR)/unpack.mk