LoongArch: Add STACKTRACE support

1. Use common arch_stack_walk() infrastructure to avoid duplicated code
   and avoid taking care of the stack storage and filtering.
2. Add sched_ra (means sched return address) and sched_cfa (means sched
   call frame address) to thread_info, and store them in switch_to().
3. Add __get_wchan() implementation.

Now we can print the process stack and wait channel by cat /proc/*/stack
and /proc/*/wchan.

Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

1 files changed, 37 insertions, 0 deletions

diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c
new file mode 100644
index 000000000000..e690c1c769f2
--- /dev/null
+++ b/arch/loongarch/kernel/stacktrace.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Stack trace management functions
+ *
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+#include <linux/sched.h>
+#include <linux/stacktrace.h>
+
+#include <asm/stacktrace.h>
+#include <asm/unwind.h>
+
+void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
+		     struct task_struct *task, struct pt_regs *regs)
+{
+	unsigned long addr;
+	struct pt_regs dummyregs;
+	struct unwind_state state;
+
+	regs = &dummyregs;
+
+	if (task == current) {
+		regs->regs[3] = (unsigned long)__builtin_frame_address(0);
+		regs->csr_era = (unsigned long)__builtin_return_address(0);
+	} else {
+		regs->regs[3] = thread_saved_fp(task);
+		regs->csr_era = thread_saved_ra(task);
+	}
+
+	regs->regs[1] = 0;
+	for (unwind_start(&state, task, regs);
+	      !unwind_done(&state); unwind_next_frame(&state)) {
+		addr = unwind_get_return_address(&state);
+		if (!addr || !consume_entry(cookie, addr))
+			break;
+	}
+}