ARC: Exception Handlers Code consolidation

After the recent cleanups, all the exception handlers now have same
boilerplate prologue code. Move that into common macro.

This reduces readability but helps greatly with sharing / duplicating
entry code with ARCv2 ISA where the handlers are pretty much the same,
just the entry prologue is different (due to hardware assist).

Also while at it, add the missing FAKE_RET_FROM_EXCPN calls in couple of
places to drop down to pure kernel mode (from exception mode) before
jumping off into "C" code.

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

arch/arc/include/asm/entry.h

@@ -365,7 +365,7 @@
  * it to memory (non-SMP case) or SCRATCH0 Aux Reg (SMP).
  *
  * Before saving the full regfile - this reg is restored back, only
- * to be saved again on kernel mode stack, as part of ptregs.
+ * to be saved again on kernel mode stack, as part of pt_regs.
  *-------------------------------------------------------------*/
 .macro EXCPN_PROLOG_FREEUP_REG	reg
 #ifdef CONFIG_SMP
@@ -383,6 +383,28 @@
 #endif
 .endm
 
+/*--------------------------------------------------------------
+ * Exception Entry prologue
+ * -Switches stack to K mode (if not already)
+ * -Saves the register file
+ *
+ * After this it is safe to call the "C" handlers
+ *-------------------------------------------------------------*/
+.macro EXCEPTION_PROLOGUE
+
+	/* Need at least 1 reg to code the early exception prologue */
+	EXCPN_PROLOG_FREEUP_REG r9
+
+	/* U/K mode at time of exception (stack not switched if already K) */
+	lr  r9, [erstatus]
+
+	/* ARC700 doesn't provide auto-stack switching */
+	SWITCH_TO_KERNEL_STK
+
+	/* save the regfile */
+	SAVE_ALL_SYS
+.endm
+
 /*--------------------------------------------------------------
  * Save all registers used by Exceptions (TLB Miss, Prot-V, Mem err etc)
  * Requires SP to be already switched to kernel mode Stack

arch/arc/kernel/entry.S

@@ -267,12 +267,7 @@ ARC_EXIT handle_interrupt_level1
 
 ARC_ENTRY instr_service
 
-	EXCPN_PROLOG_FREEUP_REG r9
-
-	lr  r9, [erstatus]
-
-	SWITCH_TO_KERNEL_STK
-	SAVE_ALL_SYS
+	EXCEPTION_PROLOGUE
 
 	lr  r0, [efa]
 	mov r1, sp
@@ -289,15 +284,13 @@ ARC_EXIT instr_service
 
 ARC_ENTRY mem_service
 
-	EXCPN_PROLOG_FREEUP_REG r9
-
-	lr  r9, [erstatus]
-
-	SWITCH_TO_KERNEL_STK
-	SAVE_ALL_SYS
+	EXCEPTION_PROLOGUE
 
 	lr  r0, [efa]
 	mov r1, sp
+
+	FAKE_RET_FROM_EXCPN r9
+
 	bl  do_memory_error
 	b   ret_from_exception
 ARC_EXIT mem_service
@@ -308,11 +301,7 @@ ARC_EXIT mem_service
 
 ARC_ENTRY EV_MachineCheck
 
-	EXCPN_PROLOG_FREEUP_REG r9
-	lr  r9, [erstatus]
-
-	SWITCH_TO_KERNEL_STK
-	SAVE_ALL_SYS
+	EXCEPTION_PROLOGUE
 
 	lr  r2, [ecr]
 	lr  r0, [efa]
@@ -342,13 +331,7 @@ ARC_EXIT EV_MachineCheck
 
 ARC_ENTRY EV_TLBProtV
 
-	EXCPN_PROLOG_FREEUP_REG r9
-
-	;Which mode (user/kernel) was the system in when Exception occured
-	lr  r9, [erstatus]
-
-	SWITCH_TO_KERNEL_STK
-	SAVE_ALL_SYS
+	EXCEPTION_PROLOGUE
 
 	;---------(3) Save some more regs-----------------
 	;  vineetg: Mar 6th: Random Seg Fault issue #1
@@ -406,12 +389,7 @@ ARC_EXIT EV_TLBProtV
 ; ---------------------------------------------
 ARC_ENTRY EV_PrivilegeV
 
-	EXCPN_PROLOG_FREEUP_REG r9
-
-	lr  r9, [erstatus]
-
-	SWITCH_TO_KERNEL_STK
-	SAVE_ALL_SYS
+	EXCEPTION_PROLOGUE
 
 	lr  r0, [efa]
 	mov r1, sp
@@ -427,14 +405,13 @@ ARC_EXIT EV_PrivilegeV
 ; ---------------------------------------------
 ARC_ENTRY EV_Extension
 
-	EXCPN_PROLOG_FREEUP_REG r9
-	lr  r9, [erstatus]
-
-	SWITCH_TO_KERNEL_STK
-	SAVE_ALL_SYS
+	EXCEPTION_PROLOGUE
 
 	lr  r0, [efa]
 	mov r1, sp
+
+	FAKE_RET_FROM_EXCPN r9
+
 	bl  do_extension_fault
 	b   ret_from_exception
 ARC_EXIT EV_Extension
@@ -526,14 +503,7 @@ trap_with_param:
 
 ARC_ENTRY EV_Trap
 
-	; Need at least 1 reg to code the early exception prolog
-	EXCPN_PROLOG_FREEUP_REG r9
-
-	;Which mode (user/kernel) was the system in when intr occured
-	lr  r9, [erstatus]
-
-	SWITCH_TO_KERNEL_STK
-	SAVE_ALL_SYS
+	EXCEPTION_PROLOGUE
 
 	;------- (4) What caused the Trap --------------
 	lr     r12, [ecr]

arch/arc/mm/tlbex.S

@@ -371,13 +371,7 @@ do_slow_path_pf:
 
 	; Slow path TLB Miss handled as a regular ARC Exception
 	; (stack switching / save the complete reg-file).
-	; That requires freeing up r9
-	EXCPN_PROLOG_FREEUP_REG r9
-
-	lr  r9, [erstatus]
-
-	SWITCH_TO_KERNEL_STK
-	SAVE_ALL_SYS
+	EXCEPTION_PROLOGUE
 
 	; ------- setup args for Linux Page fault Hanlder ---------
 	mov_s r0, sp