s390: open-code s390_personality syscall

Patch series "s390: rework compat wrapper generation".

As promised, I gave this a go and changed the SYSCALL_DEFINEx()
infrastructure to always include the wrappers for doing the
31-bit argument conversion on s390 compat mode.

This does three main things:

- The UID16 rework saved a lot of duplicated code, and would
  probably make sense by itself, but is also required as
  we can no longer call sys_*() functions directly after the
  last step.

- Removing the compat_wrapper.c file is of course the main
  goal here, in order to remove the need to maintain the
  compat_wrapper.c file when new system calls get added.
  Unfortunately, this requires adding some complexity in
  syscall_wrapper.h, and trades a small reduction in source
  code lines for a small increase in binary size for
  unused wrappers.

- As an added benefit, the use of syscall_wrapper.h now makes
  it easy to change the syscall wrappers so they no longer
  see all user space register contents, similar to changes
  done in commits fa69714 ("syscalls/x86: Use 'struct pt_regs'
  based syscall calling convention for 64-bit syscalls") and
  4378a7d ("arm64: implement syscall wrappers").
  I leave the actual implementation of this for you, if you
  want to do it later.

I did not test the changes at runtime, but I looked at the
generated object code, which seems fine here and includes
the same conversions as before.

This patch(of 5):

The sys_personality function is not meant to be called from other system
calls. We could introduce an intermediate ksys_personality function,
but it does almost nothing, so this just moves the implementation into
the caller.

Link: https://lore.kernel.org/lkml/20190116131527.2071570-1-arnd@arndb.de
Link: https://lore.kernel.org/lkml/20190116131527.2071570-2-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

Author: arndb

arch/s390/kernel/sys_s390.c

@@ -79,12 +79,15 @@ SYSCALL_DEFINE5(s390_ipc, uint, call, int, first, unsigned long, second,
 
 SYSCALL_DEFINE1(s390_personality, unsigned int, personality)
 {
-	unsigned int ret;
+	unsigned int ret = current->personality;
 
 	if (personality(current->personality) == PER_LINUX32 &&
 	    personality(personality) == PER_LINUX)
 		personality |= PER_LINUX32;
-	ret = sys_personality(personality);
+
+	if (personality != 0xffffffff)
+		set_personality(personality);
+
 	if (personality(ret) == PER_LINUX32)
 		ret &= ~PER_LINUX32;