ARC: stop using pt_regs->orig_r8

Historically, pt_regs have had orig_r8, an overloaded container for
  (1) backup copy of r8 (syscall number Trap Exceptions)
  (2) additional system state: (syscall/Exception/Interrupt)

There is no point in keeping (1) since syscall number is never clobbered
in-place, in pt_regs, unlike r0 which duals as first syscall arg as well
as syscall return value and in case of syscall restart, the orig arg0
needs restoring (from orig_r0)  after having been updated in-place with
syscall ret value.

This further paves way to convert (2) to contain ECR itself (rather than
current madeup values)

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

3 files changed, 4 insertions, 16 deletions

diff --git a/arch/arc/include/asm/entry.h b/arch/arc/include/asm/entry.h
index 72a7ed47117a..de01bc842a9a 100644
--- a/arch/arc/include/asm/entry.h
+++ b/arch/arc/include/asm/entry.h
@@ -422,18 +422,7 @@
  * Save scratch regs for sys calls
  *-------------------------------------------------------------*/
 .macro SAVE_ALL_TRAP
-        /*
-         * Setup pt_regs->orig_r8.
-         * Encode syscall number (r8) in upper short word of event type (r9)
-         * N.B. #1: This is already endian safe (see ptrace.h)
-         *      #2: Only r9 can be used as scratch as it is already clobbered
-         *          and it's contents are no longer needed by the latter part
-         *          of exception prologue
-         */
-        lsl  r9, r8, 16
-        or   r9, r9, orig_r8_IS_SCALL
-
-        SAVE_ALL_EXCEPTION  r9
+        SAVE_ALL_EXCEPTION  orig_r8_IS_SCALL
 .endm
 
 /*--------------------------------------------------------------
diff --git a/arch/arc/include/asm/syscall.h b/arch/arc/include/asm/syscall.h
index 33ab3048e9b2..29de09804306 100644
--- a/arch/arc/include/asm/syscall.h
+++ b/arch/arc/include/asm/syscall.h
@@ -18,7 +18,7 @@ static inline long
 syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 {
         if (user_mode(regs) && in_syscall(regs))
-                return regs->orig_r8;
+                return regs->r8;
         else
                 return -1;
 }
@@ -26,8 +26,7 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 static inline void
 syscall_rollback(struct task_struct *task, struct pt_regs *regs)
 {
-        /* XXX: I can't fathom how pt_regs->r8 will be clobbered ? */
-        regs->r8 = regs->orig_r8;
+        regs->r0 = regs->orig_r0;
 }
 
 static inline long
diff --git a/arch/arc/include/uapi/asm/ptrace.h b/arch/arc/include/uapi/asm/ptrace.h
index 4599109f68f2..2618cc13ba75 100644
--- a/arch/arc/include/uapi/asm/ptrace.h
+++ b/arch/arc/include/uapi/asm/ptrace.h
@@ -44,7 +44,7 @@ struct user_regs_struct {
                 long r19, r18, r17, r16, r15, r14, r13;
         } callee;
         long efa;       /* break pt addr, for break points in delay slots */
-        long stop_pc;   /* give dbg stop_pc directly after checking orig_r8 */
+        long stop_pc;   /* give dbg stop_pc after ensuring brkpt trap */
 };
 #endif /* !__ASSEMBLY__ */