xtensa: use abi_* register names in the kernel exit code

Using plain register names is prone to errors when code is changed and
new calls are added between the register load and use. Change plain
register names to abi_* names in the call-heavy part of the kernel exit
code to clearly indicate what's supposed to be preserved and what's not.
Re-align code while at it.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/entry.S

@@ -462,11 +462,11 @@ KABI_W	or	a3, a3, a2
 	 * exception handler and call the exception handler.
 	 */
 
-	l32i	abi_arg1, a1, PT_EXCCAUSE	# pass EXCCAUSE
-	rsr	abi_tmp0, excsave1
-	addx4	abi_tmp0, abi_arg1, abi_tmp0
-	l32i	abi_tmp0, abi_tmp0, EXC_TABLE_DEFAULT	# load handler
-	mov	abi_arg0, a1			# pass stack frame
+	l32i		abi_arg1, a1, PT_EXCCAUSE	# pass EXCCAUSE
+	rsr		abi_tmp0, excsave1
+	addx4		abi_tmp0, abi_arg1, abi_tmp0
+	l32i		abi_tmp0, abi_tmp0, EXC_TABLE_DEFAULT	# load handler
+	mov		abi_arg0, a1			# pass stack frame
 
 	/* Call the second-level handler */
 
@@ -477,23 +477,23 @@ KABI_W	or	a3, a3, a2
 common_exception_return:
 
 #if XTENSA_FAKE_NMI
-	l32i	abi_tmp0, a1, PT_EXCCAUSE
-	movi	abi_tmp1, EXCCAUSE_MAPPED_NMI
-	l32i	abi_saved1, a1, PT_PS
-	beq	abi_tmp0, abi_tmp1, .Lrestore_state
+	l32i		abi_tmp0, a1, PT_EXCCAUSE
+	movi		abi_tmp1, EXCCAUSE_MAPPED_NMI
+	l32i		abi_saved1, a1, PT_PS
+	beq		abi_tmp0, abi_tmp1, .Lrestore_state
 #endif
 .Ltif_loop:
-	irq_save a2, a3
+	irq_save	abi_tmp0, abi_tmp1
 #ifdef CONFIG_TRACE_IRQFLAGS
 	abi_call	trace_hardirqs_off
 #endif
 
 	/* Jump if we are returning from kernel exceptions. */
 
-	l32i	abi_saved1, a1, PT_PS
-	GET_THREAD_INFO(a2, a1)
-	l32i	a4, a2, TI_FLAGS
-	_bbci.l	abi_saved1, PS_UM_BIT, .Lexit_tif_loop_kernel
+	l32i		abi_saved1, a1, PT_PS
+	GET_THREAD_INFO(abi_tmp0, a1)
+	l32i		abi_saved0, abi_tmp0, TI_FLAGS
+	_bbci.l		abi_saved1, PS_UM_BIT, .Lexit_tif_loop_kernel
 
 	/* Specific to a user exception exit:
 	 * We need to check some flags for signal handling and rescheduling,
@@ -502,75 +502,77 @@ common_exception_return:
 	 * Note that we don't disable interrupts here. 
 	 */
 
-	_bbsi.l	a4, TIF_NEED_RESCHED, .Lresched
-	movi	a2, _TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL
-	bnone	a4, a2, .Lexit_tif_loop_user
+	_bbsi.l		abi_saved0, TIF_NEED_RESCHED, .Lresched
+	movi		abi_tmp0, _TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL
+	bnone		abi_saved0, abi_tmp0, .Lexit_tif_loop_user
 
-	l32i	a4, a1, PT_DEPC
-	bgeui	a4, VALID_DOUBLE_EXCEPTION_ADDRESS, .Lrestore_state
+	l32i		abi_tmp0, a1, PT_DEPC
+	bgeui		abi_tmp0, VALID_DOUBLE_EXCEPTION_ADDRESS, .Lrestore_state
 
 	/* Call do_signal() */
 
 #ifdef CONFIG_TRACE_IRQFLAGS
 	abi_call	trace_hardirqs_on
 #endif
-	rsil	a2, 0
-	mov	abi_arg0, a1
+	rsil		abi_tmp0, 0
+	mov		abi_arg0, a1
 	abi_call	do_notify_resume	# int do_notify_resume(struct pt_regs*)
-	j	.Ltif_loop
+	j		.Ltif_loop
 
 .Lresched:
 #ifdef CONFIG_TRACE_IRQFLAGS
 	abi_call	trace_hardirqs_on
 #endif
-	rsil	a2, 0
+	rsil		abi_tmp0, 0
 	abi_call	schedule	# void schedule (void)
-	j	.Ltif_loop
+	j		.Ltif_loop
 
 .Lexit_tif_loop_kernel:
 #ifdef CONFIG_PREEMPTION
-	_bbci.l	a4, TIF_NEED_RESCHED, .Lrestore_state
+	_bbci.l		abi_saved0, TIF_NEED_RESCHED, .Lrestore_state
 
 	/* Check current_thread_info->preempt_count */
 
-	l32i	a4, a2, TI_PRE_COUNT
-	bnez	a4, .Lrestore_state
+	l32i		abi_tmp1, abi_tmp0, TI_PRE_COUNT
+	bnez		abi_tmp1, .Lrestore_state
 	abi_call	preempt_schedule_irq
 #endif
-	j	.Lrestore_state
+	j		.Lrestore_state
 
 .Lexit_tif_loop_user:
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
-	_bbci.l	a4, TIF_DB_DISABLED, 1f
+	_bbci.l		abi_saved0, TIF_DB_DISABLED, 1f
 	abi_call	restore_dbreak
 1:
 #endif
 #ifdef CONFIG_DEBUG_TLB_SANITY
-	l32i	a4, a1, PT_DEPC
-	bgeui	a4, VALID_DOUBLE_EXCEPTION_ADDRESS, .Lrestore_state
+	l32i		abi_tmp0, a1, PT_DEPC
+	bgeui		abi_tmp0, VALID_DOUBLE_EXCEPTION_ADDRESS, .Lrestore_state
 	abi_call	check_tlb_sanity
 #endif
 
 .Lrestore_state:
 #ifdef CONFIG_TRACE_IRQFLAGS
-	extui	a4, abi_saved1, PS_INTLEVEL_SHIFT, PS_INTLEVEL_WIDTH
-	bgei	a4, LOCKLEVEL, 1f
+	extui		abi_tmp0, abi_saved1, PS_INTLEVEL_SHIFT, PS_INTLEVEL_WIDTH
+	bgei		abi_tmp0, LOCKLEVEL, 1f
 	abi_call	trace_hardirqs_on
 1:
 #endif
-	/* Restore optional registers. */
+	/*
+	 * Restore optional registers.
+	 * abi_arg* are used as temporary registers here.
+	 */
 
-	load_xtregs_opt a1 a2 a4 a5 a6 a7 PT_XTREGS_OPT
+	load_xtregs_opt a1 abi_tmp0 abi_arg0 abi_arg1 abi_arg2 abi_arg3 PT_XTREGS_OPT
 
 	/* Restore SCOMPARE1 */
 
 #if XCHAL_HAVE_S32C1I
-	l32i    a2, a1, PT_SCOMPARE1
-	wsr     a2, scompare1
+	l32i		abi_tmp0, a1, PT_SCOMPARE1
+	wsr		abi_tmp0, scompare1
 #endif
-	wsr	abi_saved1, ps		/* disable interrupts */
-
-	_bbci.l	abi_saved1, PS_UM_BIT, kernel_exception_exit
+	wsr		abi_saved1, ps		/* disable interrupts */
+	_bbci.l		abi_saved1, PS_UM_BIT, kernel_exception_exit
 
 user_exception_exit: