[PATCH for-next v2 2/4] riscv: stacktrace: Introduce unwind functions

[Chen Zhongjin]

Now all riscv unwinding code is inside arch_stack_walk. It's
not same as other architectures.

Make some refactoring, to move unwinding code into unwind() and
unwind_next() functions, which walks through all stack frames
or single frame.

This patch only moves code but doesn't make any logical change.

Signed-off-by: Chen Zhongjin <chenzhongjin at huawei.com>
---
 arch/riscv/include/asm/stacktrace.h |   7 ++
 arch/riscv/kernel/stacktrace.c      | 104 ++++++++++++++++++----------
 2 files changed, 74 insertions(+), 37 deletions(-)

diff --git a/arch/riscv/include/asm/stacktrace.h b/arch/riscv/include/asm/stacktrace.h
index b6cd3eddfd38..a39e4ef1dbd5 100644
--- a/arch/riscv/include/asm/stacktrace.h
+++ b/arch/riscv/include/asm/stacktrace.h
@@ -11,6 +11,13 @@ struct stackframe {
 	unsigned long ra;
 };
 
+struct unwind_state {
+	unsigned long fp;
+	unsigned long sp;
+	unsigned long pc;
+	struct pt_regs *regs;
+};
+
 extern void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
 			   const char *loglvl);
 
diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index b51e32d50a0e..e84e21868a3e 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -16,54 +16,84 @@
 
 #ifdef CONFIG_FRAME_POINTER
 
-noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
-		  void *cookie, struct task_struct *task,
-		  struct pt_regs *regs)
+static int notrace unwind_next(struct unwind_state *state)
 {
-	unsigned long fp, sp, pc;
-	int level = 0;
+	unsigned long low, high, fp;
+	struct stackframe *frame;
 
-	if (regs) {
-		fp = frame_pointer(regs);
-		sp = user_stack_pointer(regs);
-		pc = instruction_pointer(regs);
-	} else if (task == NULL || task == current) {
-		fp = (unsigned long)__builtin_frame_address(0);
-		sp = current_stack_pointer;
-		pc = (unsigned long)arch_stack_walk;
+	fp = state->fp;
+
+	/* Validate frame pointer */
+	low = state->sp + sizeof(struct stackframe);
+	high = ALIGN(low, THREAD_SIZE);
+
+	if (fp < low || fp > high || fp & 0x7)
+		return -EINVAL;
+
+	/* Unwind stack frame */
+	frame = (struct stackframe *)fp - 1;
+	state->sp = fp;
+
+	if (state->regs && state->regs->epc == state->pc &&
+		fp & 0x7) {
+		state->fp = frame->ra;
+		state->pc = state->regs->ra;
 	} else {
-		/* task blocked in __switch_to */
-		fp = task->thread.s[0];
-		sp = task->thread.sp;
-		pc = task->thread.ra;
+		state->fp = frame->fp;
+		state->pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
+							(unsigned long *)fp - 1);
 	}
 
-	for (;;) {
-		unsigned long low, high;
-		struct stackframe *frame;
+	return 0;
+}
 
-		if (unlikely(!__kernel_text_address(pc) ||
-		   (level++ >= 1 && !consume_entry(cookie, pc))))
+static void notrace unwind(struct unwind_state *state,
+				stack_trace_consume_fn consume_entry, void *cookie)
+{
+	while (1) {
+		int ret;
+
+		if (!__kernel_text_address(state->pc))
+			break;
+
+		if (!consume_entry(cookie, state->pc))
 			break;
 
-		/* Validate frame pointer */
-		low = sp + sizeof(struct stackframe);
-		high = ALIGN(sp, THREAD_SIZE);
-		if (unlikely(fp < low || fp > high || fp & 0x7))
+		ret = unwind_next(state);
+		if (ret < 0)
 			break;
-		/* Unwind stack frame */
-		frame = (struct stackframe *)fp - 1;
-		sp = fp;
-		if (regs && (regs->epc == pc) && (frame->fp & 0x7)) {
-			fp = frame->ra;
-			pc = regs->ra;
-		} else {
-			fp = frame->fp;
-			pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
-						   (unsigned long *)(fp - 8));
-		}
+	}
+}
+
+noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
+		  void *cookie, struct task_struct *task,
+		  struct pt_regs *regs)
+{
+	struct unwind_state state;
+
+	if (task == NULL)
+		task = current;
 
+	if (regs) {
+		state.fp = frame_pointer(regs);
+		state.sp = user_stack_pointer(regs);
+		state.pc = instruction_pointer(regs);
+		state.regs = regs;
+	} else if (task == current) {
+		state.fp = (unsigned long)__builtin_frame_address(0);
+		state.sp = current_stack_pointer;
+		state.pc = (unsigned long)arch_stack_walk;
+
+		/* skip frame of arch_stack_walk */
+		unwind_next(&state);
+	} else {
+		/* task blocked in __switch_to */
+		state.fp = task->thread.s[0];
+		state.sp = task->thread.sp;
+		state.pc = task->thread.ra;
 	}
+
+	unwind(&state, consume_entry, cookie);
 }
 
 #else /* !CONFIG_FRAME_POINTER */
-- 
2.17.1