parisc: Switch user access functions to signal errors in r29 instead …

…of r8

Use register r29 instead of register r8 to signal faults when accessing
user memory. In case of faults, the fixup routine will store -EFAULT in
this register.

This change saves up to 752 bytes on a 32bit kernel, partly because the
compiler doesn't need to save and restore the old r8 value on the stack.

bloat-o-meter results for usage with r29 register:
add/remove: 0/0 grow/shrink: 23/86 up/down: 228/-980 (-752)

bloat-o-meter results for usage with r28 register:
add/remove: 0/0 grow/shrink: 28/83 up/down: 296/-956 (-660)

Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/include/asm/uaccess.h

@@ -53,15 +53,18 @@ struct exception_table_entry {
 /*
  * ASM_EXCEPTIONTABLE_ENTRY_EFAULT() creates a special exception table entry
  * (with lowest bit set) for which the fault handler in fixup_exception() will
- * load -EFAULT into %r8 for a read or write fault, and zeroes the target
+ * load -EFAULT into %r29 for a read or write fault, and zeroes the target
  * register in case of a read fault in get_user().
  */
+#define ASM_EXCEPTIONTABLE_REG	29
+#define ASM_EXCEPTIONTABLE_VAR(__variable)		\
+	register long __variable __asm__ ("r29") = 0
 #define ASM_EXCEPTIONTABLE_ENTRY_EFAULT( fault_addr, except_addr )\
 	ASM_EXCEPTIONTABLE_ENTRY( fault_addr, except_addr + 1)
 
 #define __get_user_internal(sr, val, ptr)		\
 ({							\
-	register long __gu_err __asm__ ("r8") = 0;	\
+	ASM_EXCEPTIONTABLE_VAR(__gu_err);		\
 							\
 	switch (sizeof(*(ptr))) {			\
 	case 1: __get_user_asm(sr, val, "ldb", ptr); break; \
@@ -131,7 +134,7 @@ struct exception_table_entry {
 
 #define __put_user_internal(sr, x, ptr)				\
 ({								\
-	register long __pu_err __asm__ ("r8") = 0;      	\
+	ASM_EXCEPTIONTABLE_VAR(__pu_err);		      	\
         __typeof__(*(ptr)) __x = (__typeof__(*(ptr)))(x);	\
 								\
 	switch (sizeof(*(ptr))) {				\
@@ -168,7 +171,8 @@ struct exception_table_entry {
  * gcc knows about, so there are no aliasing issues. These macros must
  * also be aware that fixups are executed in the context of the fault,
  * and any registers used there must be listed as clobbers.
- * r8 is already listed as err.
+ * The register holding the possible EFAULT error (ASM_EXCEPTIONTABLE_REG)
+ * is already listed as input and output register.
  */
 
 #define __put_user_asm(sr, stx, x, ptr)				\

arch/parisc/mm/fault.c

@@ -148,11 +148,11 @@ int fixup_exception(struct pt_regs *regs)
 		 * Fix up get_user() and put_user().
 		 * ASM_EXCEPTIONTABLE_ENTRY_EFAULT() sets the least-significant
 		 * bit in the relative address of the fixup routine to indicate
-		 * that %r8 should be loaded with -EFAULT to report a userspace
-		 * access error.
+		 * that gr[ASM_EXCEPTIONTABLE_REG] should be loaded with
+		 * -EFAULT to report a userspace access error.
 		 */
 		if (fix->fixup & 1) {
-			regs->gr[8] = -EFAULT;
+			regs->gr[ASM_EXCEPTIONTABLE_REG] = -EFAULT;
 
 			/* zero target register for get_user() */
 			if (parisc_acctyp(0, regs->iir) == VM_READ) {