[PATCH 2/2] riscv: stacktrace: make walk_stackframe() more robust

[Puranjay Mohan]

Currently walk_stackframe() provides only a cookie and the PC to the
consume_entry function. This doesn't allow the implementation of
advanced stack walkers that need access to SP and FP as well.

Change walk_stackframe to provide a struct unwind_state to the
consume_entry function. This unwind_state has all information that is
available to walk_stackframe. The information provided to the callback
will not always be live/useful, the callback would be aware of the
different configurations the information in unwind_state can be.

For example: if CONFIG_FRAME_POINTER is not available, unwind_state->fp
will always be zero.

This commit doesn't make any functional changes.

Signed-off-by: Puranjay Mohan <puranjay12 at gmail.com>
---
 arch/riscv/kernel/stacktrace.c | 55 ++++++++++++++++++++++++++++++----
 1 file changed, 49 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index e28f7b2e4b6a6..92c41c87b267b 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -14,15 +14,26 @@
 
 #include <asm/stacktrace.h>
 
+struct unwind_state {
+	unsigned long fp;
+	unsigned long sp;
+	unsigned long pc;
+	struct pt_regs *regs;
+	struct task_struct *task;
+};
+
+typedef bool (*unwind_consume_fn)(void *cookie, const struct unwind_state *state);
+
 #ifdef CONFIG_FRAME_POINTER
 
 extern asmlinkage void ret_from_exception(void);
 
 static __always_inline void
 walk_stackframe(struct task_struct *task, struct pt_regs *regs,
-		bool (*fn)(void *, unsigned long), void *arg)
+		unwind_consume_fn fn, void *arg)
 {
 	unsigned long fp, sp, pc;
+	struct unwind_state state;
 	int level = 0;
 
 	if (regs) {
@@ -40,12 +51,17 @@ walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 		sp = task->thread.sp;
 		pc = task->thread.ra;
 	}
+	state.task = task;
+	state.regs = regs;
 
 	for (;;) {
 		unsigned long low, high;
 		struct stackframe *frame;
 
-		if (unlikely(!__kernel_text_address(pc) || (level++ >= 0 && !fn(arg, pc))))
+		state.sp = sp;
+		state.fp = fp;
+		state.pc = pc;
+		if (unlikely(!__kernel_text_address(pc) || (level++ >= 0 && !fn(arg, &state))))
 			break;
 
 		/* Validate frame pointer */
@@ -64,7 +80,10 @@ walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 			pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
 						   &frame->ra);
 			if (pc == (unsigned long)ret_from_exception) {
-				if (unlikely(!__kernel_text_address(pc) || !fn(arg, pc)))
+				state.sp = sp;
+				state.fp = fp;
+				state.pc = pc;
+				if (unlikely(!__kernel_text_address(pc) || !fn(arg, &state)))
 					break;
 
 				pc = ((struct pt_regs *)sp)->epc;
@@ -79,9 +98,10 @@ walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 
 static __always_inline void
 walk_stackframe(struct task_struct *task, struct pt_regs *regs,
-		bool (*fn)(void *, unsigned long), void *arg)
+		unwind_consume_fn fn, void *arg)
 {
 	unsigned long sp, pc;
+	struct unwind_state state;
 	unsigned long *ksp;
 
 	if (regs) {
@@ -99,9 +119,14 @@ walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 	if (unlikely(sp & 0x7))
 		return;
 
+	state.task = task;
+	state.regs = regs;
+	state.sp = sp;
+	state.fp = 0;
 	ksp = (unsigned long *)sp;
 	while (!kstack_end(ksp)) {
-		if (__kernel_text_address(pc) && unlikely(!fn(arg, pc)))
+		state.pc = pc;
+		if (__kernel_text_address(pc) && unlikely(!fn(arg, &state)))
 			break;
 		pc = READ_ONCE_NOCHECK(*ksp++) - 0x4;
 	}
@@ -109,10 +134,28 @@ walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 
 #endif /* CONFIG_FRAME_POINTER */
 
+struct unwind_consume_entry_data {
+	stack_trace_consume_fn consume_entry;
+	void *cookie;
+};
+
+static __always_inline bool
+arch_unwind_consume_entry(void *cookie, const struct unwind_state *state)
+{
+	struct unwind_consume_entry_data *data = cookie;
+
+	return data->consume_entry(data->cookie, state->pc);
+}
+
 noinline noinstr void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
 				      struct task_struct *task, struct pt_regs *regs)
 {
-	walk_stackframe(task, regs, consume_entry, cookie);
+	struct unwind_consume_entry_data data = {
+		.consume_entry = consume_entry,
+		.cookie = cookie,
+	};
+
+	walk_stackframe(task, regs, arch_unwind_consume_entry, &data);
 }
 
 static bool print_trace_address(void *arg, unsigned long pc)
-- 
2.40.1