arch: arc: use top of isr stack as exception stack and bug fixes

* re-use top of isr stack as exception stack
* bug fixes in irq offload's implementation
* improve kernel oops implementation

Signed-off-by: Wayne Ren <[email protected]>

Author: Wayne Ren

arch/arc/core/fatal.c

@@ -81,11 +81,6 @@ void _NanoFatalErrorHandler(unsigned int reason, const NANO_ESF *pEsf)
 	_SysFatalErrorHandler(reason, pEsf);
 }
 
-void _do_kernel_oops(const NANO_ESF *esf)
-{
-	_NanoFatalErrorHandler(esf->r0, esf);
-}
-
 FUNC_NORETURN void _arch_syscall_oops(void *ssf_ptr)
 {
 	_SysFatalErrorHandler(_NANO_ERR_KERNEL_OOPS, ssf_ptr);

arch/arc/core/fault.c

@@ -39,6 +39,13 @@ void _Fault(const NANO_ESF *esf)
 	code =  _ARC_V2_ECR_CODE(ecr);
 	parameter = _ARC_V2_ECR_PARAMETER(ecr);
 
+
+	/* exception raised by kernel */
+	if (vector == 0x9 && parameter == _TRAP_S_CALL_RUNTIME_EXCEPT) {
+		_NanoFatalErrorHandler(esf->r0, esf);
+		return;
+	}
+
 	printk("Exception vector: 0x%x, cause code: 0x%x, parameter 0x%x\n",
 	       vector, code, parameter);
 	printk("Address 0x%x\n", exc_addr);

arch/arc/core/fault_s.S

@@ -33,17 +33,18 @@ GTEXT(__ev_extension)
 GTEXT(__ev_div_zero)
 GTEXT(__ev_dc_error)
 GTEXT(__ev_maligned)
+#ifdef CONFIG_IRQ_OFFLOAD
+GTEXT(_irq_do_offload);
+#endif
 
 GDATA(exc_nest_count)
 
 	.balign 4
 SECTION_VAR(BSS, saved_value)
 	.word 0
 
-#define EXCEPTION_STACK_SIZE 256
-
-SECTION_VAR(NOINIT, _exception_stack)
-	.space EXCEPTION_STACK_SIZE
+/* the necessary stack size for exception handling */
+#define EXCEPTION_STACK_SIZE 384
 
 /*
  * @brief Fault handler installed in the fault and reserved vectors
@@ -62,6 +63,7 @@ SECTION_SUBSEC_FUNC(TEXT,__fault,__ev_div_zero)
 SECTION_SUBSEC_FUNC(TEXT,__fault,__ev_dc_error)
 SECTION_SUBSEC_FUNC(TEXT,__fault,__ev_maligned)
 
+_exc_entry:
 
 #ifdef CONFIG_ARC_STACK_CHECKING
 	st r0, [saved_value]
@@ -72,10 +74,24 @@ SECTION_SUBSEC_FUNC(TEXT,__fault,__ev_maligned)
 	ld r0, [saved_value]
 #endif
 	st sp, [saved_value]
-	mov_s sp, _exception_stack
+	/*
+	 * re-use the top part of interrupt stack as exception
+	 * stack. If this top part is used by interrupt handling,
+	 * and exception is raised, then here it's guaranteed that
+	 * exception handling has necessary stack to use
+	 */
+	mov_s sp, _interrupt_stack
 	add sp, sp, EXCEPTION_STACK_SIZE
 
-	/* save caller saved registers */
+	/*
+	 * save caller saved registers
+	 * this stack frame is set up in exception stack,
+	 * not in the original sp (thread stack or interrupt stack).
+	 * Because the exception may be raised by stack checking or
+	 * mpu protect violation related to stack. If this stack frame
+	 * is setup in original sp, double exception may be raised during
+	 * _create_irq_stack_frame, which is unrecoverable.
+	 */
 	_create_irq_stack_frame
 
 #ifdef CONFIG_ARC_HAS_SECURE
@@ -87,8 +103,8 @@ SECTION_SUBSEC_FUNC(TEXT,__fault,__ev_maligned)
 	lr r0,[_ARC_V2_ERET]
 	st_s r0, [sp, ___isf_t_pc_OFFSET] /* eret into pc */
 
+	/* sp is parameter of _Fault */
 	mov r0, sp
-
 	jl _Fault
 
 _exc_return:
@@ -138,18 +154,13 @@ _exc_return_from_exc:
 	rtie
 
 
-#ifdef CONFIG_IRQ_OFFLOAD
-GTEXT(_irq_do_offload);
-#endif
-
-
 SECTION_SUBSEC_FUNC(TEXT,__fault,__ev_trap)
 	/* get the id of trap_s */
 	lr ilink, [_ARC_V2_ECR]
 	and ilink, ilink, 0x3f
 #ifdef CONFIG_USERSPACE
 	cmp ilink, _TRAP_S_CALL_SYSTEM_CALL
-	bne _do_other_trap
+	bne _do_non_syscall_trap
 /* do sys_call */
 	mov ilink, _SYSCALL_LIMIT
 	cmp r6, ilink
@@ -177,27 +188,16 @@ valid_syscall_id:
 
 	rtie
 
+_do_non_syscall_trap:
+#endif /* CONFIG_USERSPACE */
+#ifdef CONFIG_IRQ_OFFLOAD
 	/*
-	 * Before invoking exception handler, the kernel switches to an exception
-	 * stack to save the faulting thread's registers.
-	 * The exception is fatal and all the kernel can do is just print
-	 * a diagnostic message and halt.
+	 * IRQ_OFFLOAD is to simulate interrupt handling through exception,
+	 * so its entry is different with normal exception handling, it is
+	 * handled in isr stack
 	 */
-
-_do_other_trap:
-#endif /* CONFIG_USERSPACE */
-#ifdef CONFIG_ARC_STACK_CHECKING
-	st r0, [saved_value]
-	/* disable stack checking */
-	lr r0, [_ARC_V2_STATUS32]
-	bclr r0, r0, _ARC_V2_STATUS32_SC_BIT
-	kflag r0
-	ld r0, [saved_value]
-#endif
-	st sp, [saved_value]
-	mov_s sp, _exception_stack
-	add sp, sp, EXCEPTION_STACK_SIZE
-
+	cmp ilink, _TRAP_S_SCALL_IRQ_OFFLOAD
+	bne _exc_entry
 	/* save caller saved registers */
 	_create_irq_stack_frame
 
@@ -210,21 +210,83 @@ _do_other_trap:
 	lr r0,[_ARC_V2_ERET]
 	st_s r0, [sp, ___isf_t_pc_OFFSET] /* eret into pc */
 
+#ifdef CONFIG_ARC_STACK_CHECKING
+	/* disable stack checking */
+	lr r0, [_ARC_V2_STATUS32]
+	bclr r0, r0, _ARC_V2_STATUS32_SC_BIT
+	kflag r0
+#endif
+
+	ld r1, [exc_nest_count]
+	add r0, r1, 1
+	st r0, [exc_nest_count]
+	cmp r1, 0
+
+	bgt.d  exc_nest_handle
 	mov r0, sp
 
-	mov blink,  _exc_return
+	mov r1, _kernel
+	ld sp, [r1, _kernel_offset_to_irq_stack]
+exc_nest_handle:
+	push_s r0
 
-	cmp ilink, _TRAP_S_CALL_RUNTIME_EXCEPT
-	beq _oops
+	jl _irq_do_offload
 
-#ifdef CONFIG_IRQ_OFFLOAD
-	cmp ilink, _TRAP_S_SCALL_IRQ_OFFLOAD
-	bne _trap_fault
-	j _irq_do_offload
+	pop sp
+
+	mov	r1, exc_nest_count
+	ld	r0, [r1]
+	sub	r0, r0, 1
+	cmp	r0, 0
+	bne.d	_exc_return_from_exc
+	st 	r0, [r1]
+
+#ifdef CONFIG_PREEMPT_ENABLED
+	mov_s r1, _kernel
+	ld_s r2, [r1, _kernel_offset_to_current]
+
+	/* check if the current thread needs to be rescheduled */
+	ld_s r0, [r1, _kernel_offset_to_ready_q_cache]
+	breq r0, r2, _exc_return_from_irqoffload_trap
+
+	_save_callee_saved_regs
+
+	st _CAUSE_RIRQ, [r2, _thread_offset_to_relinquish_cause]
+	/* note: Ok to use _CAUSE_RIRQ since everything is saved */
+
+	ld_s r2, [r1, _kernel_offset_to_ready_q_cache]
+	st_s r2, [r1, _kernel_offset_to_current]
+
+#ifdef CONFIG_ARC_HAS_SECURE
+	/*
+	 * sync up the ERSEC_STAT.ERM and SEC_STAT.IRM.
+	 * use a fake interrupt return to simulate an exception turn.
+	 * ERM and IRM record which mode the cpu should return, 1: secure
+	 * 0: normal
+	 */
+	lr r3,[_ARC_V2_ERSEC_STAT]
+	btst r3, 31
+	bset.nz r3, r3, 3
+	bclr.z r3, r3, 3
+	/* sflag r3 */
+	/* sflag instruction is not supported in current ARC GNU */
+	.long 0x00ff302f
 #endif
+	/* clear AE bit to forget this was an exception */
+	lr r3, [_ARC_V2_STATUS32]
+	and r3,r3,(~_ARC_V2_STATUS32_AE)
+	kflag r3
+	/* pretend lowest priority interrupt happened to use common handler */
+	lr r3, [_ARC_V2_AUX_IRQ_ACT]
+	or r3,r3,(1<<(CONFIG_NUM_IRQ_PRIO_LEVELS-1)) /* use lowest */
+	sr r3, [_ARC_V2_AUX_IRQ_ACT]
 
-_trap_fault:
-	j _Fault
+	/* Assumption: r2 has current thread */
+	b _rirq_common_interrupt_swap
+#endif
 
-_oops:
-	j _do_kernel_oops
+_exc_return_from_irqoffload_trap:
+	_pop_irq_stack_frame
+	rtie
+#endif /* CONFIG_IRQ_OFFLOAD */
+	b _exc_entry