ARM: aarch64: implement stacktraces

Implement stacktraces as a great debugging aid. On aarch64 this is cheap
enough to be enabled unconditionally. Unwinding code is taken from the
Kernel.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 86 insertions, 0 deletions

diff --git a/arch/arm/lib64/stacktrace.c b/arch/arm/lib64/stacktrace.c
new file mode 100644
index 0000000000..b8352c1454
--- /dev/null
+++ b/arch/arm/lib64/stacktrace.c
@@ -0,0 +1,86 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; version 2.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ */
+
+#include <common.h>
+#include <asm/stacktrace.h>
+
+#define THREAD_SIZE 16384
+
+/*
+ * AArch64 PCS assigns the frame pointer to x29.
+ *
+ * A simple function prologue looks like this:
+ * 	sub	sp, sp, #0x10
+ *   	stp	x29, x30, [sp]
+ *	mov	x29, sp
+ *
+ * A simple function epilogue looks like this:
+ *	mov	sp, x29
+ *	ldp	x29, x30, [sp]
+ *	add	sp, sp, #0x10
+ */
+int unwind_frame(struct stackframe *frame)
+{
+	unsigned long high, low;
+	unsigned long fp = frame->fp;
+
+	low  = frame->sp;
+	high = ALIGN(low, THREAD_SIZE);
+
+	if (fp < low || fp > high - 0x18 || fp & 0xf)
+		return -EINVAL;
+
+	frame->sp = fp + 0x10;
+	frame->fp = *(unsigned long *)(fp);
+	frame->pc = *(unsigned long *)(fp + 8);
+
+	return 0;
+}
+
+void dump_backtrace_entry(unsigned long where, unsigned long from)
+{
+#ifdef CONFIG_KALLSYMS
+	printf("[<%08lx>] (%pS) from [<%08lx>] (%pS)\n", where, (void *)where, from, (void *)from);
+#else
+	printf("Function entered at [<%08lx>] from [<%08lx>]\n", where, from);
+#endif
+}
+
+void unwind_backtrace(struct pt_regs *regs)
+{
+        struct stackframe frame = {};
+	register unsigned long current_sp asm ("sp");
+
+	if (regs) {
+		frame.fp = regs->regs[29];
+		frame.pc = regs->elr;
+	} else {
+		frame.fp = (unsigned long)__builtin_frame_address(0);
+		frame.sp = current_sp;
+		frame.pc = (unsigned long)unwind_backtrace;
+	}
+
+	printf("Call trace:\n");
+	while (1) {
+		unsigned long where = frame.pc;
+		int ret;
+
+		ret = unwind_frame(&frame);
+		if (ret < 0)
+			break;
+		dump_backtrace_entry(where, frame.pc);
+	}
+}
+
+void dump_stack(void)
+{
+	unwind_backtrace(NULL);
+}