Device/docs/design/build-system.html is a good start point to understand Android build system. In this topic, I will describe the behind details using mm to compile an executable and shared library.
Basic
In envsetup.sh, mm macro is defined.
function mm()
{
# If we're sitting in the root of the build tree, just do a
# normal make.
if [ -f config/envsetup.make -a -f Makefile ]; then
make $@
else
# Find the closest Android.mk file.
T=$(gettop)
M=$(findmakefile)
if [ ! "$T" ]; then
echo "Couldn't locate the top of the tree. Try setting TOP."
elif [ ! "$M" ]; then
echo "Couldn't locate a makefile from the current directory."
else
ONE_SHOT_MAKEFILE=$M make -C $T files $@
fi
fi
}
In top layer Makefile
ifneq ($(ONE_SHOT_MAKEFILE),)
# We've probably been invoked by the "mm" shell function
# with a subdirectory's makefile.
include $(ONE_SHOT_MAKEFILE)
# Change CUSTOM_MODULES to include only modules that were
# defined by this makefile; this will install all of those
# modules as a side-effect. Do this after including ONE_SHOT_MAKEFILE
# so that the modules will be installed in the same place they
# would have been with a normal make.
CUSTOM_MODULES := $(sort $(call get-tagged-modules,$(ALL_MODULE_TAGS),))
FULL_BUILD :=
INTERNAL_DEFAULT_DOCS_TARGETS :=
# Stub out the notice targets, which probably aren't defined
# when using ONE_SHOT_MAKEFILE.
NOTICE-HOST-%: ;
NOTICE-TARGET-%: ;
So if we type mm in a directory, it will finally include our own Android.mk. Android will put every Android.mk into one huge Makefile.
In top layer Makefile, it includes base_rules.make, while in base_rules.make it defines a target for LOCAL_MODULE which must be specified in our own Android.mk.
# Provide a short-hand for building this module.
# We name both BUILT and INSTALLED in case
# LOCAL_UNINSTALLABLE_MODULE is set.
.PHONY: $(LOCAL_MODULE)
$(LOCAL_MODULE): $(LOCAL_BUILT_MODULE) $(LOCAL_INSTALLED_MODULE)
definitions.make contains the most important macros for building source file. Here lists the two macros for building C++ and C source files.
###########################################################
## Commands for running gcc to compile a C++ file
###########################################################
define transform-cpp-to-o
@mkdir -p $(dir $@)
@echo "target $(PRIVATE_ARM_MODE) C++: $(PRIVATE_MODULE) <= $<"
$(hide) $(PRIVATE_CXX) /
$(foreach incdir, /
$(if $(PRIVATE_NO_DEFAULT_COMPILER_FLAGS),, /
$(TARGET_PROJECT_INCLUDES) /
$(TARGET_C_INCLUDES) /
) /
$(PRIVATE_C_INCLUDES) /
, /
-I $(incdir) /
) /
-c /
$(if $(PRIVATE_NO_DEFAULT_COMPILER_FLAGS),, /
$(TARGET_GLOBAL_CFLAGS) /
$(TARGET_GLOBAL_CPPFLAGS) /
$(PRIVATE_ARM_CFLAGS) /
) /
$(PRIVATE_CFLAGS) /
$(PRIVATE_CPPFLAGS) /
$(PRIVATE_DEBUG_CFLAGS) /
-fno-rtti /
-MD -o $@ $<
$(hide) $(transform-d-to-p)
endef
###########################################################
## Commands for running gcc to compile a C file
###########################################################
# $(1): extra flags
define transform-c-or-s-to-o-no-deps
@mkdir -p $(dir $@)
$(hide) $(PRIVATE_CC) /
$(foreach incdir, /
$(if $(PRIVATE_NO_DEFAULT_COMPILER_FLAGS),, /
$(TARGET_PROJECT_INCLUDES) /
$(TARGET_C_INCLUDES) /
) /
$(PRIVATE_C_INCLUDES) /
, /
-I $(incdir) /
) /
-c /
$(if $(PRIVATE_NO_DEFAULT_COMPILER_FLAGS),, /
$(TARGET_GLOBAL_CFLAGS) /
$(PRIVATE_ARM_CFLAGS) /
) /
$(PRIVATE_CFLAGS) /
$(1) /
$(PRIVATE_DEBUG_CFLAGS) /
-MD -o $@ $<
endef
Executable
In our own Android.mk we should add two lines.
LOCAL_MODULE := ***
include $(BUILD_EXECUTABLE)
BUILD_EXECUTALE is defined in config.make.
BUILD_EXECUTABLE:= $(BUILD_SYSTEM)/executable.make
In executable.make
include $(BUILD_SYSTEM)/dynamic_binary.make
ifeq ($(LOCAL_FORCE_STATIC_EXECUTABLE),true)
$(linked_module): $(TARGET_CRTBEGIN_STATIC_O) $(all_objects) $(all_libraries) $(TARGET_CRTEND_O)
$(transform-o-to-static-executable)
else
$(linked_module): $(TARGET_CRTBEGIN_DYNAMIC_O) $(all_objects) $(all_libraries) $(TARGET_CRTEND_O)
$(transform-o-to-executable)
Endif
So here defined a new target $(linked_module).
transform-o-to-exeuctable macro is defined in defintions.make.
define transform-o-to-executable
@mkdir -p $(dir $@)
@echo "target Executable: $(PRIVATE_MODULE) ($@)"
$(hide) $(transform-o-to-executable-inner)
endef
combo/linux-arm.make contains macros to transform o to executable for ARM.
define transform-o-to-executable-inner
$(TARGET_CXX) -nostdlib -Bdynamic -Wl,-T,$(BUILD_SYSTEM)/armelf.x /
-Wl,-dynamic-linker,/system/bin/linker /
-Wl,--gc-sections /
-Wl,-z,nocopyreloc /
-o $@ /
$(TARGET_GLOBAL_LD_DIRS) /
-Wl,-rpath-link=$(TARGET_OUT_INTERMEDIATE_LIBRARIES) /
$(call normalize-target-libraries,$(PRIVATE_ALL_SHARED_LIBRARIES)) /
$(TARGET_CRTBEGIN_DYNAMIC_O) /
$(PRIVATE_ALL_OBJECTS) /
$(call normalize-target-libraries,$(PRIVATE_ALL_STATIC_LIBRARIES)) /
$(PRIVATE_LDFLAGS) /
$(TARGET_LIBGCC) /
$(TARGET_CRTEND_O)
endef
binary.make contains some PRIVATE_* definitions used by the above macros.
$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_YACCFLAGS := $(LOCAL_YACCFLAGS)
$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_ASFLAGS := $(LOCAL_ASFLAGS)
$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_CFLAGS := $(LOCAL_CFLAGS)
$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_CPPFLAGS := $(LOCAL_CPPFLAGS)
$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_DEBUG_CFLAGS := $(debug_cflags)
$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_C_INCLUDES := $(LOCAL_C_INCLUDES)
$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_LDFLAGS := $(LOCAL_LDFLAGS)
$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_LDLIBS := $(LOCAL_LDLIBS)
combo/linux-arm.make contains default CFLAGS/CPPFLAGS/C_INCLUDES definitions.
$(combo_target)GLOBAL_CFLAGS += /
-march=armv5te -mtune=xscale /
-msoft-float -fpic /
-mthumb-interwork /
-ffunction-sections /
-funwind-tables /
-fstack-protector /
-D__ARM_ARCH_5__ -D__ARM_ARCH_5T__ /
-D__ARM_ARCH_5E__ -D__ARM_ARCH_5TE__ /
-include include/arch/linux-arm/AndroidConfig.h
$(combo_target)GLOBAL_CPPFLAGS += -fvisibility-inlines-hidden
$(combo_target)RELEASE_CFLAGS := /
-DSK_RELEASE -DNDEBUG /
-O2 -g /
-Wstrict-aliasing=2 /
-finline-functions /
-fno-inline-functions-called-once /
-fgcse-after-reload /
-frerun-cse-after-loop /
-frename-registers
# unless CUSTOM_KERNEL_HEADERS is defined, we're going to use
# symlinks located in out/ to point to the appropriate kernel
# headers. see 'config/kernel_headers.make' for more details
#
KERNEL_HEADERS_COMMON := system/bionic/kernel/common
KERNEL_HEADERS_ARCH := system/bionic/kernel/arch-$(TARGET_ARCH)
ifneq ($(CUSTOM_KERNEL_HEADERS),)
KERNEL_HEADERS_COMMON := $(CUSTOM_KERNEL_HEADERS)
KERNEL_HEADERS_ARCH := $(CUSTOM_KERNEL_HEADERS)
endif
KERNEL_HEADERS := $(KERNEL_HEADERS_COMMON) $(KERNEL_HEADERS_ARCH)
$(combo_target)C_INCLUDES := /
system/bionic/arch-arm/include /
system/bionic/include /
system/libstdc++/include /
$(KERNEL_HEADERS) /
system/libm/include /
system/libm/include/arch/arm /
system/libthread_db/include
Shared Library
In our own Android.mk we should add two lines.
LOCAL_MODULE := ***
include $(BUILD_SHARED_LIBRARY)
BUILD_SHARED_LIBRARY is defined in config.make.
BUILD_SHARED_LIBRARY:= $(BUILD_SYSTEM)/shared_library.make
In shared_library.make
include $(BUILD_SYSTEM)/dynamic_binary.make
$(linked_module): $(all_objects) $(all_libraries) $(LOCAL_ADDITIONAL_DEPENDENCIES)
$(transform-o-to-shared-lib)
So here defined a new target $(linked_module).
transform-o-to-shared-lib macro is defined in defintions.make.
define transform-o-to-shared-lib
@mkdir -p $(dir $@)
@echo "target SharedLib: $(PRIVATE_MODULE) ($@)"
$(hide) $(transform-o-to-shared-lib-inner)
endef
combo/linux-arm.make contains macro to transform o to shared lib for ARM.
define transform-o-to-shared-lib-inner
$(TARGET_CXX) /
-nostdlib -Wl,-soname,$(notdir $@) -Wl,-T,$(BUILD_SYSTEM)/armelf.xsc /
-Wl,--gc-sections /
-Wl,-shared,-Bsymbolic /
$(TARGET_GLOBAL_LD_DIRS) /
$(PRIVATE_ALL_OBJECTS) /
-Wl,--whole-archive /
$(call normalize-host-libraries,$(PRIVATE_ALL_WHOLE_STATIC_LIBRARIES)) /
-Wl,--no-whole-archive /
$(call normalize-target-libraries,$(PRIVATE_ALL_STATIC_LIBRARIES)) /
$(call normalize-target-libraries,$(PRIVATE_ALL_SHARED_LIBRARIES)) /
-o $@ /
$(PRIVATE_LDFLAGS) /
$(TARGET_LIBGCC)
endef
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