Messages in this thread Patch in this message | | | From | Masahiro Yamada <> | Subject | [PATCH] samples: binderfs: really compile this sample and fix build issues | Date | Sun, 7 Jun 2020 12:20:53 +0900 |
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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 to have 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 include path.
I added 'depends on HEADERS_INSTALL' in Kconfig, and '-I usr/include' compiler flag in Makefile.
[2] compile the sample for target architecture
Since headers_install works for the target architecture, only the native build 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 'ifndef CROSS_COMPILE' will go away.
I added 'depends on CC_CAN_LINK' because $(CC) is not necessarily capable of linking user-space programs.
[3] use subdir-y to descend into samples/binderfs/
Since this directory does not contain any kernel-space code, it has no point to generate built-in.a or modules.order.
Replace obj-$(CONFIG_...) with subdir-$(CONFIG_...).
[4] -Wunused-variable warning
If I compile this, I see the following warning.
samples/binderfs/binderfs_example.c: In function 'main': samples/binderfs/binderfs_example.c:21:9: warning: unused variable 'len' [-Wunused-variable] 21 | size_t len; | ^~~
I removed the unused 'len'.
[5] CONFIG_ANDROID_BINDERFS is not required
Since this is a user-space standalone program, it is independent of the kernel configuration.
Remove 'depends on ANDROID_BINDERFS'.
Fixes: 9762dc1432e1 ("samples: add binderfs sample program") Fixes: c624adc9cb6e ("samples: fix binderfs sample") Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> ---
samples/Kconfig | 2 +- samples/Makefile | 2 +- samples/binderfs/Makefile | 9 ++++----- samples/binderfs/binderfs_example.c | 1 - 4 files changed, 6 insertions(+), 8 deletions(-)
diff --git a/samples/Kconfig b/samples/Kconfig index 0cbb6146f3cf..953abbdebf7b 100644 --- a/samples/Kconfig +++ b/samples/Kconfig @@ -185,7 +185,7 @@ config SAMPLE_VFIO_MDEV_MBOCHS config SAMPLE_ANDROID_BINDERFS bool "Build Android binderfs example" - depends on ANDROID_BINDERFS + depends on CC_CAN_LINK && HEADERS_INSTALL help Builds a sample program to illustrate the use of the Android binderfs filesystem. diff --git a/samples/Makefile b/samples/Makefile index 29c66aadd954..4029d207cebb 100644 --- a/samples/Makefile +++ b/samples/Makefile @@ -2,7 +2,7 @@ # Makefile for Linux samples code subdir-$(CONFIG_SAMPLE_AUXDISPLAY) += auxdisplay -obj-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs/ +subdir-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs 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 -ifndef CROSS_COMPILE -ifdef CONFIG_SAMPLE_ANDROID_BINDERFS -hostprogs := binderfs_example -endif -endif +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); -- 2.25.1
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