xtensa: rework kernel oops exception path

When kernel OOPS is raised, we need to actually go through
the process of terminating the offending thread, instead of
simply printing the stack and continue running. This change
employs similar mechanism to xtensa_arch_except() to use
illegal instruction to raise hardware exception, and going
through the fatal exception path.

Signed-off-by: Daniel Leung <[email protected]>
Signed-off-by: Flavio Ceolin <[email protected]>

Author: dcpleung

arch/xtensa/core/fatal.c

@@ -87,6 +87,8 @@ char *z_xtensa_exccause(unsigned int cause_code)
 	case 63:
 		/* i.e. z_except_reason */
 		return "zephyr exception";
+	case 64:
+		return "kernel oops";
 	default:
 		return "unknown/reserved";
 	}
@@ -114,7 +116,6 @@ void z_xtensa_fatal_error(unsigned int reason, const z_arch_esf_t *esf)
 		z_xtensa_backtrace_print(100, (int *)esf);
 #endif
 #endif
-
 		arch_irq_unlock(key);
 	}
 
@@ -144,9 +145,10 @@ FUNC_NORETURN void z_system_halt(unsigned int reason)
 
 FUNC_NORETURN void arch_syscall_oops(void *ssf)
 {
-	z_arch_esf_t *esf = ssf;
+	ARG_UNUSED(ssf);
+
+	xtensa_arch_kernel_oops(K_ERR_KERNEL_OOPS, ssf);
 
-	z_xtensa_fatal_error(K_ERR_KERNEL_OOPS, esf);
 	CODE_UNREACHABLE;
 }
 

arch/xtensa/core/xtensa-asm2-util.S

@@ -204,6 +204,20 @@ xtensa_arch_except_epc:
 	ill
 	retw
 
+/*
+ * void xtensa_arch_kernel_oops(int reason_p, void *ssf);
+ *
+ * Simply to raise hardware exception for Kernel OOPS.
+ */
+.global xtensa_arch_kernel_oops
+.global xtensa_arch_kernel_oops_epc
+.align 4
+xtensa_arch_kernel_oops:
+	entry a1, 16
+xtensa_arch_kernel_oops_epc:
+	ill
+	retw
+
 /*
  * void xtensa_switch(void *new, void **old_return);
  *

arch/xtensa/core/xtensa-asm2.c

@@ -20,6 +20,7 @@
 LOG_MODULE_DECLARE(os, CONFIG_KERNEL_LOG_LEVEL);
 
 extern char xtensa_arch_except_epc[];
+extern char xtensa_arch_kernel_oops_epc[];
 
 #ifdef CONFIG_USERSPACE
 Z_EXC_DECLARE(z_xtensa_user_string_nlen);
@@ -202,11 +203,12 @@ static inline unsigned int get_bits(int offset, int num_bits, unsigned int val)
 	return val & mask;
 }
 
-static void print_fatal_exception(_xtensa_irq_bsa_t *bsa, int cause,
+static void print_fatal_exception(void *print_stack, int cause,
 				  bool is_dblexc, uint32_t depc)
 {
 	void *pc;
 	uint32_t ps, vaddr;
+	_xtensa_irq_bsa_t *bsa = (void *)*(int **)print_stack;
 
 	ps = bsa->ps;
 	pc = (void *)bsa->pc;
@@ -334,7 +336,7 @@ void *xtensa_excint1_c(int *interrupted_stack)
 	bool is_fatal_error = false;
 	bool is_dblexc = false;
 	uint32_t ps;
-	void *pc;
+	void *pc, *print_stack = (void *)interrupted_stack;
 	uint32_t depc = 0;
 
 	__asm__ volatile("rsr.exccause %0" : "=r"(cause));
@@ -399,22 +401,40 @@ void *xtensa_excint1_c(int *interrupted_stack)
 		 * We assign EXCCAUSE the unused, reserved code 63; this may be
 		 * problematic if the app or new boards also decide to repurpose
 		 * this code.
+		 *
+		 * Another intentionally ill is from xtensa_arch_kernel_oops.
+		 * Kernel OOPS has to be explicity raised so we can simply
+		 * set the reason and continue.
 		 */
-		if ((pc ==  (void *) &xtensa_arch_except_epc) && (cause == 0)) {
-			cause = 63;
-			__asm__ volatile("wsr.exccause %0" : : "r"(cause));
-			reason = bsa->a2;
+		if (cause == EXCCAUSE_ILLEGAL) {
+			if (pc == (void *)&xtensa_arch_except_epc) {
+				cause = 63;
+				__asm__ volatile("wsr.exccause %0" : : "r"(cause));
+				reason = bsa->a2;
+			} else if (pc == (void *)&xtensa_arch_kernel_oops_epc) {
+				cause = 64; /* kernel oops */
+				reason = K_ERR_KERNEL_OOPS;
+
+				/* A3 contains the second argument to
+				 * xtensa_arch_kernel_oops(reason, ssf)
+				 * where ssf is the stack frame causing
+				 * the kernel oops.
+				 */
+				print_stack = (void *)bsa->a3;
+			}
 		}
 
-		print_fatal_exception(bsa, cause, is_dblexc, depc);
+		if (reason != K_ERR_KERNEL_OOPS) {
+			print_fatal_exception(print_stack, cause, is_dblexc, depc);
+		}
 
 		/* FIXME: legacy xtensa port reported "HW" exception
 		 * for all unhandled exceptions, which seems incorrect
 		 * as these are software errors.  Should clean this
 		 * up.
 		 */
 		z_xtensa_fatal_error(reason,
-				     (void *)interrupted_stack);
+				     (void *)print_stack);
 		break;
 	}
 

include/zephyr/arch/xtensa/arch.h

@@ -54,6 +54,7 @@ struct arch_mem_domain {
 };
 
 extern void xtensa_arch_except(int reason_p);
+extern void xtensa_arch_kernel_oops(int reason_p, void *ssf);
 
 #ifdef CONFIG_USERSPACE