riscv: add backtrace support

When debugging, it is useful to have a backtrace to find
out what is in the call stack as the previous function (RA)
may not have been the culprit.

Since this adds size to the build, do not add it by default
and avoid putting it in the SPL build if not needed.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Tested-by: Leo Yu-Chi Liang <ycliang@andestech.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/arch/riscv/lib/interrupts.c b/arch/riscv/lib/interrupts.c
index a26ccc721fd..7350e2ced85 100644
--- a/arch/riscv/lib/interrupts.c
+++ b/arch/riscv/lib/interrupts.c
@@ -60,6 +60,40 @@ static void show_regs(struct pt_regs *regs)
 #endif
 }
 
+#if defined(CONFIG_FRAMEPOINTER) || defined(CONFIG_SPL_FRAMEPOINTER)
+static void show_backtrace(struct pt_regs *regs)
+{
+	uintptr_t *fp = (uintptr_t *)regs->s0;
+	unsigned count = 0;
+	ulong ra;
+
+	printf("backtrace:\n");
+
+	/* there are a few entry points where the s0 register is
+	 * set to gd, so to avoid changing those, just abort if
+	 * the value is the same */
+	while (fp != NULL && fp != (uintptr_t *)gd) {
+		ra = fp[-1];
+		printf("backtrace %2d: FP: " REG_FMT " RA: " REG_FMT,
+		       count, (ulong)fp, ra);
+
+		if (gd && gd->flags & GD_FLG_RELOC)
+			printf(" - RA: " REG_FMT " reloc adjusted\n",
+			ra - gd->reloc_off);
+		else
+			printf("\n");
+
+		fp = (uintptr_t *)fp[-2];
+		count++;
+	}
+}
+#else
+static void show_backtrace(struct pt_regs *regs)
+{
+	printf("No backtrace support enabled\n");
+}
+#endif
+
 /**
  * instr_len() - get instruction length
  *
@@ -131,6 +165,7 @@ static void _exit_trap(ulong code, ulong epc, ulong tval, struct pt_regs *regs)
 		       epc - gd->reloc_off, regs->ra - gd->reloc_off);
 
 	show_regs(regs);
+	show_backtrace(regs);
 	show_code(epc);
 	show_efi_loaded_images(epc);
 	panic("\n");