parisc: Clean up fixup routines for get_user()/put_user()

Al Viro noticed that userspace accesses via get_user()/put_user() can be
simplified a lot with regard to usage of the exception handling.

This patch implements a fixup routine for get_user() and put_user() in such
that the exception handler will automatically load -EFAULT into the register
%r8 (the error value) in case on a fault on userspace.  Additionally the fixup
routine will zero the target register on fault in case of a get_user() call.
The target register is extracted out of the faulting assembly instruction.

This patch brings a few benefits over the old implementation:
1. Exception handling gets much cleaner, easier and smaller in size.
2. Helper functions like fixup_get_user_skip_1 (all of fixup.S) can be dropped.
3. No need to hardcode %r9 as target register for get_user() any longer. This
   helps the compiler register allocator and thus creates less assembler
   statements.
4. No dependency on the exception_data contents any longer.
5. Nested faults will be handled cleanly.

Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Cc: <stable@vger.kernel.org> # v4.9+
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/lib/Makefile

@@ -2,7 +2,7 @@
 # Makefile for parisc-specific library files
 #
 
-lib-y	:= lusercopy.o bitops.o checksum.o io.o memset.o fixup.o memcpy.o \
+lib-y	:= lusercopy.o bitops.o checksum.o io.o memset.o memcpy.o \
 	   ucmpdi2.o delay.o
 
 obj-y	:= iomap.o

arch/parisc/lib/fixup.S

@@ -1,98 +0,0 @@
-/*
- * Linux/PA-RISC Project (http://www.parisc-linux.org/)
- *
- *  Copyright (C) 2004  Randolph Chung <tausq@debian.org>
- *
- *    This program is free software; you can redistribute it and/or modify
- *    it under the terms of the GNU General Public License as published by
- *    the Free Software Foundation; either version 2, or (at your option)
- *    any later version.
- *
- *    This program is distributed in the hope that it will be useful,
- *    but WITHOUT ANY WARRANTY; without even the implied warranty of
- *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *    GNU General Public License for more details.
- *
- *    You should have received a copy of the GNU General Public License
- *    along with this program; if not, write to the Free Software
- *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- * 
- * Fixup routines for kernel exception handling.
- */
-#include <asm/asm-offsets.h>
-#include <asm/assembly.h>
-#include <asm/errno.h>
-#include <linux/linkage.h>
-
-#ifdef CONFIG_SMP
-	.macro  get_fault_ip t1 t2
-	loadgp
-	addil LT%__per_cpu_offset,%r27
-	LDREG RT%__per_cpu_offset(%r1),\t1
-	/* t2 = smp_processor_id() */
-	mfctl 30,\t2
-	ldw TI_CPU(\t2),\t2
-#ifdef CONFIG_64BIT
-	extrd,u \t2,63,32,\t2
-#endif
-	/* t2 = &__per_cpu_offset[smp_processor_id()]; */
-	LDREGX \t2(\t1),\t2 
-	addil LT%exception_data,%r27
-	LDREG RT%exception_data(%r1),\t1
-	/* t1 = this_cpu_ptr(&exception_data) */
-	add,l \t1,\t2,\t1
-	/* %r27 = t1->fault_gp - restore gp */
-	LDREG EXCDATA_GP(\t1), %r27
-	/* t1 = t1->fault_ip */
-	LDREG EXCDATA_IP(\t1), \t1
-	.endm
-#else
-	.macro  get_fault_ip t1 t2
-	loadgp
-	/* t1 = this_cpu_ptr(&exception_data) */
-	addil LT%exception_data,%r27
-	LDREG RT%exception_data(%r1),\t2
-	/* %r27 = t2->fault_gp - restore gp */
-	LDREG EXCDATA_GP(\t2), %r27
-	/* t1 = t2->fault_ip */
-	LDREG EXCDATA_IP(\t2), \t1
-	.endm
-#endif
-
-	.level LEVEL
-
-	.text
-	.section .fixup, "ax"
-
-	/* get_user() fixups, store -EFAULT in r8, and 0 in r9 */
-ENTRY_CFI(fixup_get_user_skip_1)
-	get_fault_ip %r1,%r8
-	ldo 4(%r1), %r1
-	ldi -EFAULT, %r8
-	bv %r0(%r1)
-	copy %r0, %r9
-ENDPROC_CFI(fixup_get_user_skip_1)
-
-ENTRY_CFI(fixup_get_user_skip_2)
-	get_fault_ip %r1,%r8
-	ldo 8(%r1), %r1
-	ldi -EFAULT, %r8
-	bv %r0(%r1)
-	copy %r0, %r9
-ENDPROC_CFI(fixup_get_user_skip_2)
-
-	/* put_user() fixups, store -EFAULT in r8 */
-ENTRY_CFI(fixup_put_user_skip_1)
-	get_fault_ip %r1,%r8
-	ldo 4(%r1), %r1
-	bv %r0(%r1)
-	ldi -EFAULT, %r8
-ENDPROC_CFI(fixup_put_user_skip_1)
-
-ENTRY_CFI(fixup_put_user_skip_2)
-	get_fault_ip %r1,%r8
-	ldo 8(%r1), %r1
-	bv %r0(%r1)
-	ldi -EFAULT, %r8
-ENDPROC_CFI(fixup_put_user_skip_2)
-