Re: [PATCH 2/2] selftests/userfaultfd: improve syscall number definition

Hi Shuah, Andrea,

On 22/09/15 15:06, Andrea Arcangeli wrote:

On Tue, Sep 22, 2015 at 07:49:13AM -0600, Shuah Khan wrote:

quoted

On 09/22/2015 04:45 AM, Andre Przywara wrote:

quoted

At the moment the userfaultfd test program only supports x86 and an
architecture called "powewrpc" ;-)
Fix that typo and add the syscall numbers for other architectures as
well.
Also as in an ideal world a syscall number should come from the system
header file <asm/unistd.h>, include that header and guard the explicit
syscall number section below to avoid redefinitions.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 tools/testing/selftests/vm/userfaultfd.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
index 2c7cca6..63be27f 100644
--- a/tools/testing/selftests/vm/userfaultfd.c
+++ b/tools/testing/selftests/vm/userfaultfd.c

@@ -65,16 +65,27 @@
 #include <sys/ioctl.h>
 #include <pthread.h>
 #include "../../../../include/uapi/linux/userfaultfd.h"
+#include <asm/unistd.h>
 
+/* ideally the above user header provides that number, but ... */
+#ifndef __NR_userfaultfd
 #ifdef __x86_64__
 #define __NR_userfaultfd 323
 #elif defined(__i386__)
 #define __NR_userfaultfd 374
-#elif defined(__powewrpc__)
+#elif defined(__powerpc__)
 #define __NR_userfaultfd 364
+#elif defined(__ia64__)
+#define __NR_userfaultfd 1343
+#elif defined(__arm__)
+#define __NR_userfaultfd 388
+#elif defined(__aarch64__)
+/* this is from the generic syscall table, used also on other architectures */
+#define __NR_userfaultfd 283
 #else
 #error "missing __NR_userfaultfd definition"
 #endif
+#endif /* !__NR_userfaultfd */
 
 static unsigned long nr_cpus, nr_pages, nr_pages_per_cpu, page_size;
 

This is not okay. User-space shouldn't be (re)defining/duplicating
syscall numbers. I can't take this patch.

While I agree that this isn't the right approach from a userland point
of view, I wonder how this is supposed to work for the next few months?
Is everybody required to overwrite their distribution-provided kernel
headers just for compiling this test program?

-mm has already been updated to do exactly that. Syscall numbers end
up hardcoded into userland binaries/libs somewhere, so it's not a
bugfix but certainly it's a nice cleanup to remove the whole #ifdef block.

Andre, could you see if linux-next (which includes -mm) works for you
by just running "cd tools/testing/selftests/vm/ && make"? If there's
any further change required could you diff it against linux-next?

This doesn't compile now for me, because it looks into
/usr/include/asm/unistd.h, which I keep to the distribution copy of it.
Also linux/userfaultfd.h is missing, because it's brand new.

If that tool lives in the kernel repo, it should be able to either use
the uapi headers directly or hardcode the syscall numbers - strictly
it's not a sane userland program anymore, but for that kind of tools I
deem it's totally acceptable. I think this is one rationale for keeping
it inside the linux.git repo.

Obviously you were facing the same problem in the beginning (looking at
the original code), so I was just extending the original solution to
cover more architectures and prepare for the time when those symbols
start to appear in distributions.

I guess the right solution would be to hack the Makefile to set the
include path to the kernel's copy of include/uapi, though I am not sure
this works cleanly for different architectures and separate build
directories. I will give this a try ...

Cheers,
Andre.