tools: add options to optimize host binaries

Mains goals are:
- reduce binary size of host tools;
- reduce i/o load on build host;
- increase performance of host tools being built.

Signed-off-by: Konstantin Demin <rockdrilla@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/18659
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

config/Config-devel.in

@@ -62,6 +62,60 @@ menuconfig DEVEL
 		  Compile all host host tools even if not needed. This is needed to prepare a
 		  universal precompiled host tools archive to use in another buildroot.
 
+	menuconfig OPTIMIZE_HOST_TOOLS
+		bool "Host Tools compile options" if DEVEL
+
+		if OPTIMIZE_HOST_TOOLS
+
+		config HOST_FLAGS_OPT
+			string "Host Tools optimization flags"
+			default "-O2"
+			help
+			  Compiler flags which are used to build host tools.
+
+			  E.g.: "-O2", "-O3 -fno-tree-vectorize".
+
+			  Default is "-O2".
+
+		config HOST_TOOLS_STRIP
+			bool "Strip Host Tools"
+			help
+			  Instructs compiler/linker to use flags from HOST_FLAGS_STRIP
+			  in order to reduce binary size of host tools.
+
+		config HOST_FLAGS_STRIP
+			string "Host Tools compiler/linker flags for stripping symbols"
+			depends on HOST_TOOLS_STRIP
+			default "-Wl,-s"
+			help
+			  Compiler flags which are used to strip symbols from host tools.
+
+			  Each flag should be prefixed with "-Wl," string
+			  because compiler (GCC) passes this value to linker.
+
+			  Default is "-Wl,-s" which means "strip all symbols" - specifically,
+			  debug symbols and other symbols not needed for relocation processing.
+
+		comment "Host Tools miscellaneous flags"
+
+		config HOST_EXTRA_CFLAGS
+			string "Host Tools extra CFLAGS"
+			default ""
+
+		config HOST_EXTRA_CXXFLAGS
+			string "Host Tools extra CXXFLAGS"
+			default ""
+
+		config HOST_EXTRA_CPPFLAGS
+			string "Host Tools extra CPPFLAGS"
+			default ""
+
+		config HOST_EXTRA_LDFLAGS
+			string "Host Tools extra LDFLAGS"
+			default ""
+
+		endif
+
 	config BUILD_SUFFIX
 		string "Build suffix to append to the target BUILD_DIR variable" if DEVEL
 		default ""

rules.mk

@@ -278,12 +278,19 @@ PKG_CONFIG:=$(STAGING_DIR_HOST)/bin/pkg-config
 
 export PKG_CONFIG
 
+HOST_FLAGS_OPT:=$(call qstrip,$(CONFIG_HOST_FLAGS_OPT))
+HOST_FLAGS_STRIP:=$(call qstrip,$(CONFIG_HOST_FLAGS_STRIP))
+HOST_EXTRA_CFLAGS:=$(call qstrip,$(CONFIG_HOST_EXTRA_CFLAGS))
+HOST_EXTRA_CXXFLAGS:=$(call qstrip,$(CONFIG_HOST_EXTRA_CXXFLAGS))
+HOST_EXTRA_CPPFLAGS:=$(call qstrip,$(CONFIG_HOST_EXTRA_CPPFLAGS))
+HOST_EXTRA_LDFLAGS:=$(call qstrip,$(CONFIG_HOST_EXTRA_LDFLAGS))
+
 HOSTCC:=$(STAGING_DIR_HOST)/bin/gcc
 HOSTCXX:=$(STAGING_DIR_HOST)/bin/g++
-HOST_CPPFLAGS:=-I$(STAGING_DIR_HOST)/include $(if $(IS_PACKAGE_BUILD),-I$(STAGING_DIR_HOSTPKG)/include -I$(STAGING_DIR)/host/include)
+HOST_CPPFLAGS:=$(strip -I$(STAGING_DIR_HOST)/include $(if $(IS_PACKAGE_BUILD),-I$(STAGING_DIR_HOSTPKG)/include -I$(STAGING_DIR)/host/include) $(HOST_EXTRA_CPPFLAGS))
-HOST_CFLAGS:=-O2 $(HOST_CPPFLAGS)
+HOST_CFLAGS:=$(strip $(HOST_FLAGS_OPT) $(HOST_EXTRA_CFLAGS) $(HOST_CPPFLAGS) $(HOST_FLAGS_STRIP))
-HOST_CXXFLAGS:=$(HOST_CFLAGS)
+HOST_CXXFLAGS:=$(strip $(HOST_CFLAGS) $(HOST_EXTRA_CXXFLAGS))
-HOST_LDFLAGS:=-L$(STAGING_DIR_HOST)/lib $(if $(IS_PACKAGE_BUILD),-L$(STAGING_DIR_HOSTPKG)/lib -L$(STAGING_DIR)/host/lib)
+HOST_LDFLAGS:=$(strip -L$(STAGING_DIR_HOST)/lib $(if $(IS_PACKAGE_BUILD),-L$(STAGING_DIR_HOSTPKG)/lib -L$(STAGING_DIR)/host/lib) $(HOST_EXTRA_LDFLAGS) $(HOST_FLAGS_STRIP))
 
 BUILD_KEY=$(TOPDIR)/key-build
 BUILD_KEY_APK_SEC=$(TOPDIR)/private-key.pem