path: root/samples
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authorMasahiro Yamada <>2020-06-07 12:20:53 +0900
committerMasahiro Yamada <>2020-06-11 20:14:41 +0900
commitfca5e94921d50d13ee8720ce58a352e7fc0228bf (patch)
treeccf9a5ce140637611db02869116a8c5a2505d0d2 /samples
parentb29482fde649c72441d5478a4ea2c52c56d97a5e (diff)
samples: binderfs: really compile this sample and fix build issues
Even after commit c624adc9cb6e ("samples: fix binderfs sample"), this sample is never compiled. 'hostprogs' teaches Kbuild that this is a host program, but not enough to order to compile it. You must add it to 'always-y' to really compile it. Since this sample has never been compiled in upstream, various issues are left unnoticed. [1] compilers without <linux/android/binderfs.h> are still widely used <linux/android/binderfs.h> is only available since commit c13295ad219d ("binderfs: rename header to binderfs.h"), i.e., Linux 5.0 If your compiler is based on UAPI headers older than Linux 5.0, you will see the following error: samples/binderfs/binderfs_example.c:16:10: fatal error: linux/android/binderfs.h: No such file or directory #include <linux/android/binderfs.h> ^~~~~~~~~~~~~~~~~~~~~~~~~~ compilation terminated. You cannot rely on compilers having such a new header. The common approach is to install UAPI headers of this kernel into usr/include, and then add it to the header search path. I added 'depends on HEADERS_INSTALL' in Kconfig, and '-I usr/include' compiler flag in Makefile. [2] compile the sample for target architecture Because headers_install works for the target architecture, only the native compiler was able to build sample code that requires '-I usr/include'. Commit 7f3a59db274c ("kbuild: add infrastructure to build userspace programs") added the new syntax 'userprogs' to compile user-space programs for the target architecture. Use it, and then 'ifndef CROSS_COMPILE' will go away. I added 'depends on CC_CAN_LINK' because $(CC) is not necessarily capable of linking user-space programs. [3] use subdir-y to descend into samples/binderfs Since this directory does not contain any kernel-space code, it has no point in generating built-in.a or modules.order. Replace obj-$(CONFIG_...) with subdir-$(CONFIG_...). [4] -Wunused-variable warning If I compile this, I see the following warning. samples/binderfs/binderfs_example.c: In function 'main': samples/binderfs/binderfs_example.c:21:9: warning: unused variable 'len' [-Wunused-variable] 21 | size_t len; | ^~~ I removed the unused 'len'. [5] CONFIG_ANDROID_BINDERFS is not required Since this is a user-space standalone program, it is independent of the kernel configuration. Remove 'depends on ANDROID_BINDERFS'. Fixes: 9762dc1432e1 ("samples: add binderfs sample program") Fixes: c624adc9cb6e ("samples: fix binderfs sample") Signed-off-by: Masahiro Yamada <> Acked-by: Christian Brauner <>
Diffstat (limited to 'samples')
4 files changed, 6 insertions, 8 deletions
diff --git a/samples/Kconfig b/samples/Kconfig
index 0cbb6146f3cf..953abbdebf7b 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -185,7 +185,7 @@ config SAMPLE_VFIO_MDEV_MBOCHS
bool "Build Android binderfs example"
Builds a sample program to illustrate the use of the Android binderfs
diff --git a/samples/Makefile b/samples/Makefile
index 29c66aadd954..4029d207cebb 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -2,7 +2,7 @@
# Makefile for Linux samples code
subdir-$(CONFIG_SAMPLE_AUXDISPLAY) += auxdisplay
obj-$(CONFIG_SAMPLE_CONFIGFS) += configfs/
obj-$(CONFIG_SAMPLE_CONNECTOR) += connector/
subdir-$(CONFIG_SAMPLE_HIDRAW) += hidraw
diff --git a/samples/binderfs/Makefile b/samples/binderfs/Makefile
index a3ac5476338a..989e4badaee2 100644
--- a/samples/binderfs/Makefile
+++ b/samples/binderfs/Makefile
@@ -1,6 +1,5 @@
# SPDX-License-Identifier: GPL-2.0-only
-hostprogs := binderfs_example
+userprogs := binderfs_example
+always-y := $(userprogs)
+userccflags += -I usr/include
diff --git a/samples/binderfs/binderfs_example.c b/samples/binderfs/binderfs_example.c
index 5bbd2ebc0aea..0fd92cdda460 100644
--- a/samples/binderfs/binderfs_example.c
+++ b/samples/binderfs/binderfs_example.c
@@ -18,7 +18,6 @@
int main(int argc, char *argv[])
int fd, ret, saved_errno;
- size_t len;
struct binderfs_device device = { 0 };
ret = unshare(CLONE_NEWNS);