[Buildroot] [PATCH 09/23] linux: build out of tree when LINUX_OVERRIDE_SRCDIR is set

[Florian Fainelli via buildroot <buildroot@buildroot.org>]

Introduce <pkg>_SUPPORTS_OUT_OF_TREE. For a package that sets it and
has <pkg>_OVERRIDE_SRCDIR defined:

 - <pkg>_SRCDIR is the overridden directory, used in place: nothing is
   rsynced into $(BUILD_DIR), only the pre/post rsync hooks still run;
 - the source-related stamp files (rsynced, patched, ...) live in the
   build directory so that nothing is created in the user's tree;
 - kconfig packages start from the source directory with O=<builddir>,
   which makes kbuild generate its wrapper Makefile in the build
   directory, so that all the existing -C $(LINUX_DIR) invocations keep
   working unmodified.

Enable it for the Linux kernel. The source tree must be clean (no
in-tree .config, include/config, arch/*/include/generated).

Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 linux/linux.mk         |  4 ++++
 package/pkg-generic.mk | 30 ++++++++++++++++++++++--------
 package/pkg-kconfig.mk |  6 +++++-
 3 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/linux/linux.mk b/linux/linux.mk
index a90e09afe906..ffec32154222 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -6,6 +6,10 @@
 
 LINUX_VERSION = $(call qstrip,$(BR2_LINUX_KERNEL_VERSION))
 LINUX_LICENSE = GPL-2.0
+
+# When LINUX_OVERRIDE_SRCDIR is set, build out of tree: no rsync of the
+# sources, the kernel is built in $(BUILD_DIR)/linux-custom with O=.
+LINUX_SUPPORTS_OUT_OF_TREE = YES
 LINUX_LICENSE_FILES = $(call qstrip,$(BR2_LINUX_KERNEL_LICENSE_FILES))
 
 LINUX_CPE_ID_VENDOR = linux
diff --git a/package/pkg-generic.mk b/package/pkg-generic.mk
index 138fe9ccef4f..c8f532e1c3e6 100644
--- a/package/pkg-generic.mk
+++ b/package/pkg-generic.mk
@@ -221,11 +221,11 @@ $(SRC_DIR)/%/.stamp_extracted:
 # used.
 $(SRC_DIR)/%/.stamp_rsynced:
 	@$(call step_start,rsync)
-	@$(call MESSAGE,"Syncing from source dir $(SRCDIR)")
+	@$(call MESSAGE,"$(if $($(PKG)_OUT_OF_TREE),Using out-of-tree source dir,Syncing from source dir) $(SRCDIR)")
 	@mkdir -p $(@D)
 	$(foreach hook,$($(PKG)_PRE_RSYNC_HOOKS),$(call $(hook))$(sep))
 	@test -d $(SRCDIR) || (echo "ERROR: $(SRCDIR) does not exist" ; exit 1)
-	rsync -au --chmod=u=rwX,go=rX $($(PKG)_OVERRIDE_SRCDIR_RSYNC_EXCLUSIONS) $(RSYNC_VCS_EXCLUSIONS) $(call qstrip,$(SRCDIR))/ $(@D)
+	$(if $($(PKG)_OUT_OF_TREE),,rsync -au --chmod=u=rwX,go=rX $($(PKG)_OVERRIDE_SRCDIR_RSYNC_EXCLUSIONS) $(RSYNC_VCS_EXCLUSIONS) $(call qstrip,$(SRCDIR))/ $(@D))
 	$(foreach hook,$($(PKG)_POST_RSYNC_HOOKS),$(call $(hook))$(sep))
 	@$(call step_end,rsync)
 	$(Q)touch $@
@@ -559,13 +559,27 @@ ifndef $(2)_STRIP_COMPONENTS
 endif
 
 $(2)_SRCDIR = $$($(2)_DIR)
-$(2)_BUILDDIR = $$($(2)_DIR)
+$(2)_BUILDDIR ?= $$($(2)_DIR)
 $(2)_SRCSUBDIR = $$($(2)_SRCDIR)/$$($(2)_SUBDIR)
 
 ifneq ($$($(2)_OVERRIDE_SRCDIR),)
 $(2)_VERSION = custom
 endif
 
+# Packages that set <pkg>_SUPPORTS_OUT_OF_TREE = YES can be built out of
+# tree when their source directory is overridden: the sources are used
+# where they are (no rsync), and only the build directory lives in
+# $(BUILD_DIR). The source-related stamp files must then not be created
+# in the (user-owned) source directory, so they live in the build directory.
+$(2)_STAMP_SRCDIR = $$($(2)_SRCDIR)
+ifneq ($$($(2)_OVERRIDE_SRCDIR),)
+ifeq ($$($(3)_SUPPORTS_OUT_OF_TREE),YES)
+$(2)_OUT_OF_TREE = YES
+$(2)_SRCDIR = $$(abspath $$(call qstrip,$$($(2)_OVERRIDE_SRCDIR)))
+$(2)_STAMP_SRCDIR = $$($(2)_BUILDDIR)
+endif
+endif
+
 ifndef $(2)_SOURCE
  ifdef $(3)_SOURCE
   $(2)_SOURCE = $$($(3)_SOURCE)
@@ -844,11 +858,11 @@ $(2)_TARGET_INSTALL_IMAGES =	$$($(2)_BUILDDIR)/.stamp_images_installed
 $(2)_TARGET_INSTALL_HOST =	$$($(2)_BUILDDIR)/.stamp_host_installed
 $(2)_TARGET_BUILD =		$$($(2)_BUILDDIR)/.stamp_built
 $(2)_TARGET_CONFIGURE =		$$($(2)_BUILDDIR)/.stamp_configured
-$(2)_TARGET_RSYNC =		$$($(2)_SRCDIR)/.stamp_rsynced
-$(2)_TARGET_PATCH =		$$($(2)_SRCDIR)/.stamp_patched
-$(2)_TARGET_EXTRACT =		$$($(2)_SRCDIR)/.stamp_extracted
-$(2)_TARGET_SOURCE =		$$($(2)_SRCDIR)/.stamp_downloaded
-$(2)_TARGET_ACTUAL_SOURCE =	$$($(2)_SRCDIR)/.stamp_actual_downloaded
+$(2)_TARGET_RSYNC =		$$($(2)_STAMP_SRCDIR)/.stamp_rsynced
+$(2)_TARGET_PATCH =		$$($(2)_STAMP_SRCDIR)/.stamp_patched
+$(2)_TARGET_EXTRACT =		$$($(2)_STAMP_SRCDIR)/.stamp_extracted
+$(2)_TARGET_SOURCE =		$$($(2)_STAMP_SRCDIR)/.stamp_downloaded
+$(2)_TARGET_ACTUAL_SOURCE =	$$($(2)_STAMP_SRCDIR)/.stamp_actual_downloaded
 $(2)_TARGET_DIRCLEAN =		$$($(2)_BUILDDIR)/.stamp_dircleaned
 
 # default extract command
diff --git a/package/pkg-kconfig.mk b/package/pkg-kconfig.mk
index 8a63d55be033..5e46c62c58e6 100644
--- a/package/pkg-kconfig.mk
+++ b/package/pkg-kconfig.mk
@@ -147,8 +147,12 @@ $$($(2)_KCONFIG_FILE) $$($(2)_KCONFIG_FRAGMENT_FILES): | $(1)-patch
 		fi; \
 	done
 
+# For an out-of-tree build, the first kconfig run is what creates the
+# wrapper Makefile in the build directory, so it must be started from
+# the source directory.
 $(2)_KCONFIG_MAKE = \
-	$$($(2)_MAKE_ENV) $$($(2)_MAKE) -C $$($(2)_BUILDDIR) \
+	$$($(2)_MAKE_ENV) $$($(2)_MAKE) \
+	$$(if $$($(2)_OUT_OF_TREE),-C $$($(2)_SRCDIR) O=$$($(2)_BUILDDIR),-C $$($(2)_BUILDDIR)) \
 		$$(PKG_KCONFIG_COMMON_OPTS) $$($(2)_KCONFIG_OPTS)
 
 # The specified source configuration file and any additional configuration file
-- 
2.34.1

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