[PATCH] riscv: Add option to print registers on exception

[Sean Anderson]

When debugging, it can be helpful to see more information about an
unhandled exception. This patch adds an option to view the registers at
the time of the trap, similar to the linux output on a kernel panic.

Signed-off-by: Sean Anderson <seanga2 at gmail.com>
---
 arch/riscv/Kconfig          |  3 +++
 arch/riscv/cpu/mtrap.S      |  3 ++-
 arch/riscv/lib/interrupts.c | 50 +++++++++++++++++++++++++++++--------
 3 files changed, 44 insertions(+), 12 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 85e15ebffa..3338b788f8 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -222,6 +222,9 @@ config XIP
 	  from a NOR flash memory without copying the code to ram.
 	  Say yes here if U-Boot boots from flash directly.

+config SHOW_REGS
+	bool "Show registers on unhandled exception"
+
 config STACK_SIZE_SHIFT
 	int
 	default 14
diff --git a/arch/riscv/cpu/mtrap.S b/arch/riscv/cpu/mtrap.S
index 407ecfa9c0..e40c7bd3f4 100644
--- a/arch/riscv/cpu/mtrap.S
+++ b/arch/riscv/cpu/mtrap.S
@@ -64,7 +64,8 @@ trap_entry:
 	SREG x31, 31 * REGBYTES(sp)
 	csrr a0, MODE_PREFIX(cause)
 	csrr a1, MODE_PREFIX(epc)
-	mv a2, sp
+	csrr a2, MODE_PREFIX(tval)
+	mv a3, sp
 	jal handle_trap
 	csrw MODE_PREFIX(epc), a0

diff --git a/arch/riscv/lib/interrupts.c b/arch/riscv/lib/interrupts.c
index 3b25c5b7a7..0f1e5123d2 100644
--- a/arch/riscv/lib/interrupts.c
+++ b/arch/riscv/lib/interrupts.c
@@ -5,6 +5,8 @@
  *
  * Copyright (C) 2017 Andes Technology Corporation
  * Rick Chen, Andes Technology Corporation <rick at andestech.com>
+ *
+ * Copyright (C) 2019 Sean Anderson <seanga2 at gmail.com>
  */

 #include <common.h>
@@ -13,7 +15,34 @@
 #include <asm/system.h>
 #include <asm/encoding.h>

-static void _exit_trap(ulong code, ulong epc, struct pt_regs *regs)
+static void show_regs(struct pt_regs *regs)
+{
+#ifdef CONFIG_SHOW_REGS
+	printf("RA: " REG_FMT " SP:  " REG_FMT " GP:  " REG_FMT "\n",
+	       regs->ra, regs->sp, regs->gp);
+	printf("TP: " REG_FMT " T0:  " REG_FMT " T1:  " REG_FMT "\n",
+	       regs->tp, regs->t0, regs->t1);
+	printf("T2: " REG_FMT " S0:  " REG_FMT " S1:  " REG_FMT "\n",
+	       regs->t2, regs->s0, regs->s1);
+	printf("A0: " REG_FMT " A1:  " REG_FMT " A2:  " REG_FMT "\n",
+	       regs->a0, regs->a1, regs->a2);
+	printf("A3: " REG_FMT " A4:  " REG_FMT " A5:  " REG_FMT "\n",
+	       regs->a3, regs->a4, regs->a5);
+	printf("A6: " REG_FMT " A7:  " REG_FMT " S2:  " REG_FMT "\n",
+	       regs->a6, regs->a7, regs->s2);
+	printf("S3: " REG_FMT " S4:  " REG_FMT " S5:  " REG_FMT "\n",
+	       regs->s3, regs->s4, regs->s5);
+	printf("S6: " REG_FMT " S7:  " REG_FMT " S8:  " REG_FMT "\n",
+	       regs->s6, regs->s7, regs->s8);
+	printf("S9: " REG_FMT " S10: " REG_FMT " S11: " REG_FMT "\n",
+	       regs->s9, regs->s10, regs->s11);
+	printf("T3: " REG_FMT " T4:  " REG_FMT " T5:  " REG_FMT "\n",
+	       regs->t3, regs->t4, regs->t5);
+	printf("T6: " REG_FMT "\n", regs->t6);
+#endif
+}
+
+static void _exit_trap(ulong code, ulong epc, ulong tval, struct pt_regs *regs)
 {
 	static const char * const exception_code[] = {
 		"Instruction address misaligned",
@@ -34,14 +63,13 @@ static void _exit_trap(ulong code, ulong epc, struct pt_regs *regs)
 		"Store/AMO page fault",
 	};

-	if (code < ARRAY_SIZE(exception_code)) {
-		printf("exception code: %ld , %s , epc %lx , ra %lx\n",
-		       code, exception_code[code], epc, regs->ra);
-	} else {
-		printf("reserved exception code: %ld , epc %lx , ra %lx\n",
-		       code, epc, regs->ra);
-	}
+	if (code < ARRAY_SIZE(exception_code))
+		printf("Unhandled exception: %s\n", exception_code[code]);
+	else
+		printf("Unhandled exception code: %ld\n", code);

+	printf("PC: " REG_FMT " TVAL: " REG_FMT "\n", epc, tval);
+	show_regs(regs);
 	hang();
 }

@@ -65,7 +93,7 @@ int disable_interrupts(void)
 	return 0;
 }

-ulong handle_trap(ulong cause, ulong epc, struct pt_regs *regs)
+ulong handle_trap(ulong cause, ulong epc, ulong tval, struct pt_regs *regs)
 {
 	ulong is_irq, irq;

@@ -83,11 +111,11 @@ ulong handle_trap(ulong cause, ulong epc, struct pt_regs *regs)
 			timer_interrupt(0);	/* handle timer interrupt */
 			break;
 		default:
-			_exit_trap(cause, epc, regs);
+			_exit_trap(cause, epc, tval, regs);
 			break;
 		};
 	} else {
-		_exit_trap(cause, epc, regs);
+		_exit_trap(cause, epc, tval, regs);
 	}

 	return epc;
-- 
2.23.0