[PATCH] samples: run headers_install for host arch instead of target arch

[Masahiro Yamada]

Some samples search headers in $(objtree)/usr/include, which is made
available by "make headers_install".  It is not kernel-space code but
host programs that need this header search path.

Commit 3fca1700c4c3 ("kbuild: make samples really depend on
headers_install") is wrong because it installs headers of the target
architecture.  Besides, UML fails to build with CONFIG_SAMPLES=y
because UML does not support headers_install.

Invoke "make headers_install" for the _host_ architecture in the
prepare stage.  Introduce CONFIG_HOST_HEADERS_INSTALL so that this
happens only for samples that need it.

I also removed 'Documentation/: headers_install', which I guess is
stale code.

Fixes: 3fca1700c4c3 ("kbuild: make samples really depend on headers_install")
Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
---

 Makefile        | 8 ++++----
 samples/Kconfig | 6 ++++++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index 0c90c43..f04564c 100644
--- a/Makefile
+++ b/Makefile
@@ -1029,10 +1029,9 @@ ifdef CONFIG_GDB_SCRIPTS
 endif
 	+$(call if_changed,link-vmlinux)
 
-# Build samples along the rest of the kernel. This needs headers_install.
+# Build samples along the rest of the kernel.
 ifdef CONFIG_SAMPLES
 vmlinux-dirs += samples
-samples: headers_install
 endif
 
 # The actual objects are generated when descending,
@@ -1098,6 +1097,9 @@ archprepare: archheaders archscripts prepare1 scripts_basic
 
 prepare0: archprepare gcc-plugins
 	$(Q)$(MAKE) $(build)=.
+ifdef CONFIG_HOST_HEADERS_INSTALL
+	$(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(SUBARCH) headers_install
+endif
 
 # All the preparing..
 prepare: prepare0 prepare-objtool
@@ -1682,8 +1684,6 @@ endif
 	$(cmd_crmodverdir)
 	$(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
 	$(build)=$(build-dir)
-# Make sure the latest headers are built for Documentation
-Documentation/ samples/: headers_install
 %/: prepare scripts FORCE
 	$(cmd_crmodverdir)
 	$(Q)$(MAKE) KBUILD_MODULES=$(if $(CONFIG_MODULES),1) \
diff --git a/samples/Kconfig b/samples/Kconfig
index bd133ef..fcd6b7c 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -1,3 +1,6 @@
+config HOST_HEADERS_INSTALL
+	bool
+
 menuconfig SAMPLES
 	bool "Sample kernel code"
 	help
@@ -95,6 +98,7 @@ config SAMPLE_CONFIGFS
 config SAMPLE_CONNECTOR
 	tristate "Build connector sample -- loadable modules only"
 	depends on CONNECTOR && m
+	select HOST_HEADERS_INSTALL
 	help
 	  When enabled, this builds both a sample kernel module for
 	  the connector interface and a user space tool to communicate
@@ -104,6 +108,7 @@ config SAMPLE_CONNECTOR
 config SAMPLE_SECCOMP
 	tristate "Build seccomp sample code -- loadable modules only"
 	depends on SECCOMP_FILTER && m
+	select HOST_HEADERS_INSTALL
 	help
 	  Build samples of seccomp filters using various methods of
 	  BPF filter construction.
@@ -149,6 +154,7 @@ config SAMPLE_VFIO_MDEV_MBOCHS
 config SAMPLE_STATX
 	bool "Build example extended-stat using code"
 	depends on BROKEN
+	select HOST_HEADERS_INSTALL
 	help
 	  Build example userspace program to use the new extended-stat syscall.
 
-- 
2.7.4