LoongArch: Add guess unwinder support

Name "guess unwinder" comes from x86, it scans the stack and reports
every kernel text address it finds.

Unwinders can be used by dump_stack() and other stacktrace functions.

Three stages when we do unwind,
  1) unwind_start(), the prapare of unwinding, fill unwind_state.
  2) unwind_done(), judge whether the unwind process is finished or not.
  3) unwind_next_frame(), unwind the next frame.

Add get_stack_info() to get stack info. At present we have irq stack and
task stack. The next_sp is the key info between two types of stacks.

Dividing unwinder helps to add new unwinders in the future.

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

1 files changed, 67 insertions, 0 deletions

diff --git a/arch/loongarch/kernel/unwind_guess.c b/arch/loongarch/kernel/unwind_guess.c
new file mode 100644
index 000000000000..5afa6064d73e
--- /dev/null
+++ b/arch/loongarch/kernel/unwind_guess.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+#include <linux/kernel.h>
+
+#include <asm/unwind.h>
+
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+	if (unwind_done(state))
+		return 0;
+	else if (state->first)
+		return state->pc;
+
+	return *(unsigned long *)(state->sp);
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+void unwind_start(struct unwind_state *state, struct task_struct *task,
+		    struct pt_regs *regs)
+{
+	memset(state, 0, sizeof(*state));
+
+	if (regs) {
+		state->sp = regs->regs[3];
+		state->pc = regs->csr_era;
+	}
+
+	state->task = task;
+	state->first = true;
+
+	get_stack_info(state->sp, state->task, &state->stack_info);
+
+	if (!unwind_done(state) && !__kernel_text_address(state->pc))
+		unwind_next_frame(state);
+}
+EXPORT_SYMBOL_GPL(unwind_start);
+
+bool unwind_next_frame(struct unwind_state *state)
+{
+	struct stack_info *info = &state->stack_info;
+	unsigned long addr;
+
+	if (unwind_done(state))
+		return false;
+
+	if (state->first)
+		state->first = false;
+
+	do {
+		for (state->sp += sizeof(unsigned long);
+		     state->sp < info->end;
+		     state->sp += sizeof(unsigned long)) {
+			addr = *(unsigned long *)(state->sp);
+
+			if (__kernel_text_address(addr))
+				return true;
+		}
+
+		state->sp = info->next_sp;
+
+	} while (!get_stack_info(state->sp, state->task, info));
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(unwind_next_frame);