[make] miscellaneous make system tweaks

-Have arch set the default optimization level. Most will use
 O2, but arm-m sets to Os.
-Make the link time garbage collection be optional. Only set
 for arm-m.

arch/arm/rules.mk

@@ -128,6 +128,8 @@ MODULE_ARM_OVERRIDE_SRCS := \
 
 GLOBAL_DEFINES += \
 	ARCH_DEFAULT_STACK_SIZE=4096
+
+ARCH_OPTFLAGS := -O2
 endif
 ifeq ($(SUBARCH),arm-m)
 MODULE_SRCS += \
@@ -140,8 +142,12 @@ MODULE_SRCS += \
 GLOBAL_INCLUDES += \
 	$(LOCAL_DIR)/arm-m/CMSIS/Include
 
+# we're building for small binaries
 GLOBAL_DEFINES += \
 	ARCH_DEFAULT_STACK_SIZE=1024
+
+ARCH_OPTFLAGS := -Os
+WITH_LINKER_GC := 1
 endif
 
 # try to find the toolchain
@@ -196,9 +202,6 @@ $(error missing MEMBASE or MEMSIZE variable, please set in target rules.mk)
 endif
 
 LIBGCC := $(shell $(TOOLCHAIN_PREFIX)gcc $(GLOBAL_COMPILEFLAGS) $(THUMBCFLAGS) -print-libgcc-file-name)
-$(info LIBGCC = $(LIBGCC))
-
-$(info GLOBAL_COMPILEFLAGS = $(GLOBAL_COMPILEFLAGS) $(THUMBCFLAGS))
 
 # potentially generated files that should be cleaned out with clean make rule
 GENERATED += \

arch/arm64/rules.mk

@@ -28,6 +28,8 @@ MODULE_SRCS += \
 GLOBAL_DEFINES += \
 	ARCH_DEFAULT_STACK_SIZE=8192
 
+ARCH_OPTFLAGS := -O2
+
 # try to find the toolchain
 ifndef TOOLCHAIN_PREFIX
 TOOLCHAIN_PREFIX := aarch64-elf-
@@ -51,9 +53,7 @@ ifeq ($(MEMVARS_SET),0)
 $(error missing MEMBASE or MEMSIZE variable, please set in target rules.mk)
 endif
 
-LIBGCC := $(shell $(TOOLCHAIN_PREFIX)gcc $(GLOBAL_COMPILEFLAGS) $(THUMBCFLAGS) -print-libgcc-file-name)
-$(info LIBGCC = $(LIBGCC))
-$(info GLOBAL_COMPILEFLAGS = $(GLOBAL_COMPILEFLAGS) $(THUMBCFLAGS))
+LIBGCC := $(shell $(TOOLCHAIN_PREFIX)gcc $(GLOBAL_COMPILEFLAGS) -print-libgcc-file-name)
 
 # potentially generated files that should be cleaned out with clean make rule
 GENERATED += \

arch/x86/rules.mk

@@ -32,6 +32,8 @@ GLOBAL_CFLAGS += $(call cc-option,$(CC),-fno-stack-protector,)
 GLOBAL_COMPILEFLAGS += -fasynchronous-unwind-tables
 GLOBAL_COMPILEFLAGS += -gdwarf-2
 
+ARCH_OPTFLAGS := -O2
+
 # potentially generated files that should be cleaned out with clean make rule
 GENERATED += \
 	$(BUILDDIR)/kernel.ld

engine.mk

@@ -44,7 +44,7 @@ OUTELF := $(BUILDDIR)/lk.elf
 CONFIGHEADER := $(BUILDDIR)/config.h
 
 GLOBAL_INCLUDES := $(BUILDDIR) $(LKROOT)/include $(addsuffix /include,$(LKINC))
-GLOBAL_OPTFLAGS ?= -Os
+GLOBAL_OPTFLAGS ?= $(ARCH_OPTFLAGS)
 GLOBAL_COMPILEFLAGS := -g -fno-builtin -finline -W -Wall -Wno-multichar -Wno-unused-parameter -Wno-unused-function -include $(CONFIGHEADER)
 GLOBAL_CFLAGS := --std=gnu99 -Werror-implicit-function-declaration -Wstrict-prototypes
 #GLOBAL_CFLAGS += -Werror
@@ -53,8 +53,6 @@ GLOBAL_CPPFLAGS := -fno-exceptions -fno-rtti -fno-threadsafe-statics
 GLOBAL_ASMFLAGS := -DASSEMBLY
 GLOBAL_LDFLAGS :=
 
-GLOBAL_COMPILEFLAGS += -ffunction-sections -fdata-sections
-GLOBAL_LDFLAGS += --gc-sections
 GLOBAL_LDFLAGS += -L $(LKROOT)
 
 # top level rule
@@ -100,6 +98,12 @@ EXTRA_OBJS :=
 # if someone defines this, the build id will be pulled into lib/version
 BUILDID ?=
 
+# if this is set to 1, use ld's garbage collector for unused functions and data
+WITH_LINKER_GC ?= 0
+
+# comment out or override if you want to see the full output of each command
+NOECHO ?= @
+
 # try to include the project file
 -include project/$(PROJECT).mk
 ifndef TARGET
@@ -172,6 +176,9 @@ CPPFILT := $(TOOLCHAIN_PREFIX)c++filt
 SIZE := $(TOOLCHAIN_PREFIX)size
 NM := $(TOOLCHAIN_PREFIX)nm
 
+# the logic to compile and link stuff is in here
+include make/build.mk
+
 # put all of the global build flags in config.h to force a rebuild if any change
 GLOBAL_DEFINES += GLOBAL_INCLUDES=\"$(subst $(SPACE),_,$(GLOBAL_INCLUDES))\"
 GLOBAL_DEFINES += GLOBAL_COMPILEFLAGS=\"$(subst $(SPACE),_,$(GLOBAL_COMPILEFLAGS))\"
@@ -181,9 +188,6 @@ GLOBAL_DEFINES += GLOBAL_CPPFLAGS=\"$(subst $(SPACE),_,$(GLOBAL_CPPFLAGS))\"
 GLOBAL_DEFINES += GLOBAL_ASMFLAGS=\"$(subst $(SPACE),_,$(GLOBAL_ASMFLAGS))\"
 GLOBAL_DEFINES += GLOBAL_LDFLAGS=\"$(subst $(SPACE),_,$(GLOBAL_LDFLAGS))\"
 
-# comment out or override if you want to see the full output of each command
-NOECHO ?= @
-
 ifneq ($(OBJS),)
 $(warning OBJS=$(OBJS))
 $(error OBJS is not empty, please convert to new module format)
@@ -201,8 +205,9 @@ $(warning CPPFLAGS=$(CPPFLAGS))
 $(error CPPFLAGS is not empty, please use GLOBAL_CPPFLAGS or MODULE_CPPFLAGS)
 endif
 
-# the logic to compile and link stuff is in here
-include make/build.mk
+$(info LIBGCC = $(LIBGCC))
+$(info GLOBAL_COMPILEFLAGS = $(GLOBAL_COMPILEFLAGS))
+$(info GLOBAL_OPTFLAGS = $(GLOBAL_OPTFLAGS))
 
 # make all object files depend on any targets in GLOBAL_SRCDEPS
 $(ALLOBJS): $(GLOBAL_SRCDEPS)

make/build.mk

@@ -1,3 +1,9 @@
+# use linker garbage collection, if requested
+ifeq ($(WITH_LINKER_GC),1)
+GLOBAL_COMPILEFLAGS += -ffunction-sections -fdata-sections
+GLOBAL_LDFLAGS += --gc-sections
+endif
+
 $(OUTBIN): $(OUTELF)
 	@echo generating image: $@
 	$(NOECHO)$(SIZE) $<