build: improve ccache support

Set CCACHE_DIR to $(TOPDIR)/.ccache and CCACHE_BASEDIR to $(TOPDIR).
This allows to do clean and dirclean. Cache hit rate for test build
after dirclean is ~65%.
If CCACHE is enabled stats are printed out at the end of building process.
CCACHE_DIR config variable allows to override default, which could be useful
when sharing cache with many builds.
cacheclean make target allows to clean the cache.

Changes from v1:
- remove ccache directory using CCACHE_DIR variable
- remove ccache leftovers from sdk and toolchain make files
- introduce CONFIG_CCACHE_DIR variable
- introduce cacheclean make target

Signed-off-by: Roman Yeryomin <roman@advem.lv>

.gitignore

@@ -28,3 +28,4 @@ TAGS*~
 git-src
 .project
 .cproject
+.ccache

Makefile

@@ -62,6 +62,11 @@ dirclean: clean
 	rm -rf $(TMP_DIR)
 	$(MAKE) -C $(TOPDIR)/scripts/config clean
 
+cacheclean:
+ifneq ($(CONFIG_CCACHE),)
+	rm -rf $(if $(call qstrip,$(CONFIG_CCACHE_DIR)),$(call qstrip,$(CONFIG_CCACHE_DIR)),$(TOPDIR)/.ccache)
+endif
+
 ifndef DUMP_TARGET_DB
 $(BUILD_DIR)/.prepared: Makefile
 	@mkdir -p $$(dirname $@)
@@ -119,6 +124,9 @@ world: prepare $(target/stamp-compile) $(package/stamp-compile) $(package/stamp-
 	$(_SINGLE)$(SUBMAKE) -r package/index
 	$(_SINGLE)$(SUBMAKE) -r json_overview_image_info
 	$(_SINGLE)$(SUBMAKE) -r checksum
+ifneq ($(CONFIG_CCACHE),)
+	$(STAGING_DIR_HOST)/bin/ccache -s
+endif
 
 .PHONY: clean dirclean prereq prepare world package/symlinks package/symlinks-install package/symlinks-clean
 

config/Config-devel.in

@@ -69,6 +69,13 @@ menuconfig DEVEL
 		help
 		  Compiler cache; see https://ccache.samba.org/
 
+	config CCACHE_DIR
+		string "Set ccache directory" if CCACHE
+		default ""
+		help
+		  Store ccache in this directory.
+		  If not set, uses './.ccache'
+
 	config EXTERNAL_KERNEL_TREE
 		string "Use external kernel tree" if DEVEL
 		default ""

include/host-build.mk

@@ -132,7 +132,9 @@ define Host/Exports/Default
   $(1) : export STAGING_PREFIX=$$(HOST_BUILD_PREFIX)
   $(1) : export PKG_CONFIG_PATH=$$(STAGING_DIR_HOST)/lib/pkgconfig:$$(HOST_BUILD_PREFIX)/lib/pkgconfig
   $(1) : export PKG_CONFIG_LIBDIR=$$(HOST_BUILD_PREFIX)/lib/pkgconfig
-  $(if $(CONFIG_CCACHE),$(1) : export CCACHE_DIR:=$(STAGING_DIR_HOST)/ccache)
+  $(if $(CONFIG_CCACHE),$(1) : export CCACHE_BASEDIR:=$(TOPDIR))
+  $(if $(CONFIG_CCACHE),$(1) : export CCACHE_DIR:=$(if $(call qstrip,$(CONFIG_CCACHE_DIR)),$(call qstrip,$(CONFIG_CCACHE_DIR)),$(TOPDIR)/.ccache))
+  $(if $(CONFIG_CCACHE),$(1) : export CCACHE_COMPILERCHECK:=%compiler% -dumpmachine; %compiler% -dumpversion)
   $(if $(HOST_CONFIG_SITE),$(1) : export CONFIG_SITE:=$(HOST_CONFIG_SITE))
   $(if $(IS_PACKAGE_BUILD),$(1) : export PATH=$$(TARGET_PATH_PKG))
 endef

include/package.mk

@@ -173,7 +173,9 @@ define Build/Exports/Default
   $(1) : export CONFIG_SITE:=$$(CONFIG_SITE)
   $(1) : export PKG_CONFIG_PATH:=$$(PKG_CONFIG_PATH)
   $(1) : export PKG_CONFIG_LIBDIR:=$$(PKG_CONFIG_PATH)
-  $(if $(CONFIG_CCACHE),$(1) : export CCACHE_DIR:=$(STAGING_DIR)/ccache)
+  $(if $(CONFIG_CCACHE),$(1) : export CCACHE_BASEDIR:=$(TOPDIR))
+  $(if $(CONFIG_CCACHE),$(1) : export CCACHE_DIR:=$(if $(call qstrip,$(CONFIG_CCACHE_DIR)),$(call qstrip,$(CONFIG_CCACHE_DIR)),$(TOPDIR)/.ccache))
+  $(if $(CONFIG_CCACHE),$(1) : export CCACHE_COMPILERCHECK:=%compiler% -dumpmachine; %compiler% -dumpversion)
 endef
 Build/Exports=$(Build/Exports/Default)
 

include/toplevel.mk

@@ -262,7 +262,7 @@ package/symlinks-clean:
 help:
 	cat README
 
-distclean:
+distclean: cacheclean
 	rm -rf bin build_dir .config* dl feeds key-build* logs package/feeds package/openwrt-packages staging_dir tmp
 	@$(_SINGLE)$(SUBMAKE) -C scripts/config clean
 

rules.mk

@@ -298,6 +298,9 @@ ifneq ($(CONFIG_CCACHE),)
   TARGET_CXX:= ccache_cxx
   HOSTCC:= ccache $(HOSTCC)
   HOSTCXX:= ccache $(HOSTCXX)
+  export CCACHE_BASEDIR:=$(TOPDIR)
+  export CCACHE_DIR:=$(if $(call qstrip,$(CONFIG_CCACHE_DIR)),$(call qstrip,$(CONFIG_CCACHE_DIR)),$(TOPDIR)/.ccache)
+  export CCACHE_COMPILERCHECK:=%compiler% -dumpmachine; %compiler% -dumpversion
 endif
 
 TARGET_CONFIGURE_OPTS = \

target/sdk/Makefile

@@ -20,7 +20,7 @@ STAGING_SUBDIR_HOST := staging_dir/host
 STAGING_SUBDIR_TARGET := staging_dir/$(TARGET_DIR_NAME)
 STAGING_SUBDIR_TOOLCHAIN := staging_dir/toolchain-$(ARCH)$(ARCH_SUFFIX)_gcc-$(GCCV)_$(LIBC)$(if $(CONFIG_arm),_eabi)
 
-EXCLUDE_DIRS:=*/ccache/* \
+EXCLUDE_DIRS:= \
 	*/stamp \
 	*/stampfiles \
 	*/man \
@@ -135,11 +135,7 @@ $(BIN_DIR)/$(SDK_NAME).tar.xz: clean
 		$(TOPDIR)/package/kernel/linux \
 		$(SDK_BUILD_DIR)/package/
 
-	-rm -rf \
+	-rm -rf $(SDK_BUILD_DIR)/$(STAGING_SUBDIR_HOST)/.prereq-build
-		$(SDK_BUILD_DIR)/$(STAGING_SUBDIR_HOST)/ccache \
-		$(SDK_BUILD_DIR)/$(STAGING_SUBDIR_TARGET)/ccache \
-		$(SDK_BUILD_DIR)/$(STAGING_SUBDIR_TOOLCHAIN)/ccache \
-		$(SDK_BUILD_DIR)/$(STAGING_SUBDIR_HOST)/.prereq-build
 
 	-rm -f $(SDK_BUILD_DIR)/feeds.conf.default
 	$(if $(BASE_FEED),echo "$(BASE_FEED)" > $(SDK_BUILD_DIR)/feeds.conf.default)

target/toolchain/Makefile

@@ -15,7 +15,7 @@ override MAKEFLAGS=
 
 TOOLCHAIN_NAME:=$(VERSION_DIST_SANITIZED)-toolchain-$(if $(CONFIG_VERSION_FILENAMES),$(VERSION_NUMBER)-)$(BOARD)$(if $(SUBTARGET),-$(SUBTARGET))_gcc-$(GCCV)$(DIR_SUFFIX).$(HOST_OS)-$(HOST_ARCH)
 TOOLCHAIN_BUILD_DIR:=$(BUILD_DIR)/$(TOOLCHAIN_NAME)
-EXCLUDE_DIRS:=*/ccache \
+EXCLUDE_DIRS:= \
 	*/initial \
 	*/stamp \
 	*/stampfiles \