ARC: [Review] Preparing to fix incorrect syscall restarts due to signals

To avoid multiple syscall restarts (multiple signals) or no restart at
all (sigreturn), we need just an extra bit of state "literally 1 bit" in
struct pt_regs. orig_r8 is the best place to do this, however given the
way it is encoded currently, we can't add anything simplistically.

Current orig_r8:
* syscalls   -> 1 to NR_SYSCALLS
* Exceptions -> NR_SYSCALLS + 1
* Break-point-> NR_SYSCALLS + 2

In new scheme it is a bit-field
* lower short word contains the  exact event type (and a new bit to represent
   restart semantics : if syscall was already / can't be restarted)
* upper short word optionally containing the syscall num - needed by
  likes of tracehooks etc

This patch only changes how orig_r8 is organised and nothing should
change behaviourily.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>

arch/arc/kernel/asm-offsets.c

@@ -46,7 +46,7 @@ int main(void)
 	BLANK();
 
 	DEFINE(PT_status32, offsetof(struct pt_regs, status32));
-	DEFINE(PT_orig_r8, offsetof(struct pt_regs, orig_r8));
+	DEFINE(PT_orig_r8, offsetof(struct pt_regs, orig_r8_word));
 	DEFINE(PT_sp, offsetof(struct pt_regs, sp));
 	DEFINE(PT_r0, offsetof(struct pt_regs, r0));
 	DEFINE(PT_r1, offsetof(struct pt_regs, r1));

arch/arc/kernel/entry.S

@@ -350,8 +350,8 @@ ARC_EXIT EV_Extension
 
 trap_with_param:
 
-	;make sure orig_r8 is a positive value
-	st  NR_syscalls + 2, [sp, PT_orig_r8]
+	; stop_pc info by gdb needs this info
+	st  orig_r8_IS_BRKPT, [sp, PT_orig_r8]
 
 	mov r0, r12
 	lr  r1, [efa]