linux: build and install kernel selftests

This patch adds the ability to compile and install the kernel
selftests into the target at /usr/lib/kselftests. The rationale behind
/usr/lib is that the selftests have subdirectories where they are
installed which makes them unsuitable to be placed in /usr/sbin as
this would result in /usr/sbin/kselftests/x/y/z. While the selftests
aren't libraries either, they don't achieve much as a standalone
binary so they can be considered to be a 'library of tests' making
/usr/lib sensible.

The selftests require that the kernel headers be installed into the
kernel build tree as some of the selftests have a hardcoded CFLAGS to
include kernel headers (CFLAGS += -I../../../../usr/include/). This is
most easily achieved by using the make ... headers_install inside the
kernel build dir.

This is likely to be a rarely used debugging/performance feature for
development and unlikely to be used in a production configuration.

Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
[Thomas:
 - remove bash as a build dependency, it is only a runtime dependency.
 - fix typo in the Config.in help text, and rewrap
 - add missing 'depends on BR2_USE_MMU' dependency for the comment.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

linux/Config.tools.in

@@ -26,4 +26,26 @@ config BR2_LINUX_KERNEL_TOOL_PERF
 
 	  https://perf.wiki.kernel.org/
 
+config BR2_LINUX_KERNEL_TOOL_SELFTESTS
+	bool"selftests"
+	depends on BR2_PACKAGE_BUSYBOX_SHOW_OTHERS # bash
+	depends on BR2_USE_MMU  # bash
+	select BR2_PACKAGE_BASH # runtime
+	select BR2_PACKAGE_POPT
+	select BR2_PACKAGE_LIBCAP_NG
+	help
+	  Build and install (to /usr/lib/kselftests) kernel selftests.
+
+	  Use of this option implies you know the process of using and
+	  compiling the kernel selftests. The Makefile to build and
+	  install these is very noisy and may appear to cause your
+	  build to fail for strange reasons.
+
+	  This is very much a use at your risk option and may not work
+	  for every setup or every architecture.
+
+comment "selftests needs BR2_PACKAGE_BUSYBOX_SHOW_OTHERS"
+	depends on BR2_USE_MMU
+	depends on !BR2_PACKAGE_BUSYBOX_SHOW_OTHERS
+
 endmenu

linux/linux-tool-selftests.mk

@@ -0,0 +1,46 @@
+################################################################################
+#
+# selftests
+#
+################################################################################
+
+LINUX_TOOLS += selftests
+
+ifeq ($(KERNEL_ARCH),x86_64)
+SELFTESTS_ARCH=x86
+else
+ifeq ($(KERNEL_ARCH),i386)
+SELFTESTS_ARCH=x86
+else
+SELFTESTS_ARCH=$(KERNEL_ARCH)
+endif
+endif
+
+SELFTESTS_DEPENDENCIES = libcap-ng popt
+
+SELFTESTS_MAKE_FLAGS = \
+	$(LINUX_MAKE_FLAGS) \
+	ARCH=$(SELFTESTS_ARCH)
+
+# O must be redefined here to overwrite the one used by Buildroot for
+# out of tree build. We build the selftests in $(@D)/tools/selftests and
+# not just $(@D) so that it isn't built in the root directory of the kernel
+# sources.
+#
+# The headers_install step here is important as some kernel selftests use a
+# hardcoded CFLAGS to find kernel headers e.g:
+# CFLAGS += -I../../../../usr/include/
+# The headers_install target will install the kernel headers locally inside
+# the Linux build dir
+define SELFTESTS_BUILD_CMDS
+	$(TARGET_MAKE_ENV) $(MAKE1) -C $(@D) $(SELFTESTS_MAKE_FLAGS) \
+		headers_install
+	$(TARGET_MAKE_ENV) $(MAKE1) -C $(@D)/tools/testing/selftests \
+		$(SELFTESTS_MAKE_FLAGS) O=$(@D)/tools/testing/selftests
+endef
+
+define SELFTESTS_INSTALL_TARGET_CMDS
+	$(TARGET_MAKE_ENV) $(MAKE1) -C $(@D)/tools/testing/selftests \
+		$(SELFTESTS_MAKE_FLAGS) O=$(@D)/tools/testing/selftests \
+		INSTALL_PATH=$(TARGET_DIR)/usr/lib/kselftests install
+endef