Add subarchitecture-independent implementation of asm-generic/syscall.h
allowing access to user system call parameters and results:
* syscall_get_nr()
* syscall_rollback()
* syscall_get_error()
* syscall_get_return_value()
* syscall_set_return_value()
* syscall_get_arguments()
* syscall_set_arguments()
* syscall_get_arch() provided by arch/x86/um/asm/syscall.h

This provides the necessary syscall helpers needed by
HAVE_ARCH_SECCOMP_FILTER plus syscall_get_error().

This is inspired from Meredydd Luff's patch
(https://gerrit.chromium.org/gerrit/21425).
Signed-off-by: NMickaël Salaün <mic@digikod.net>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: Meredydd Luff <meredydd@senatehouse.org>
Cc: David Drysdale <drysdale@google.com>
Signed-off-by: NRichard Weinberger <richard@nod.at>
Acked-by: NKees Cook <keescook@chromium.org>

I didn't realize that um didn't include x86's asm/syscall.h.
Re-add a missing typedef.
Reported-by: NRichard Weinberger <richard@nod.at>
Signed-off-by: NAndy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 034042cc ("x86/entry/syscalls: Move syscall table declarations into asm/syscalls.h")
Link: http://lkml.kernel.org/r/8d15b9a88f4fd49e3342757e0a34624ee5ce9220.1444696194.git.luto@kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

This patch defines syscall_get_arch() for the um platform.  It adds a
new syscall.h header file to define this.  It copies the HOST_AUDIT_ARCH
definition from ptrace.h.  (that definition will be removed when we
switch audit to use this new syscall_get_arch() function)
Based-on-patch-by: NRichard Briggs <rgb@redhat.com>
Signed-off-by: NEric Paris <eparis@redhat.com>
Cc: user-mode-linux-devel@lists.sourceforge.net