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

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Message-ID: <20150922140625.GH25412@redhat.com>
Date:	Tue, 22 Sep 2015 16:06:25 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Shuah Khan <shuahkh@....samsung.com>
Cc:	Andre Przywara <andre.przywara@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH 2/2] selftests/userfaultfd: improve syscall number
 definition

On Tue, Sep 22, 2015 at 07:49:13AM -0600, Shuah Khan wrote:
> On 09/22/2015 04:45 AM, Andre Przywara wrote:
> > 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@....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.

-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?

Thanks!
Andrea
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