This will be used by bpf_throw() to unwind till the program marked as
exception boundary and run the callback with the stack of the main
program.
This is required for supporting BPF exceptions on RISC-V.
This depends on the frame pointer unwinder, so it is only built under
CONFIG_FRAME_POINTER, else falls back to the weak no-op.

Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
---
 arch/riscv/kernel/stacktrace.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index b41b6255751c..a4c2411f4038 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -5,6 +5,7 @@
  */
 
 #include <linux/export.h>
+#include <linux/filter.h>
 #include <linux/kallsyms.h>
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
@@ -102,6 +103,33 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 	}
 }
 
+void notrace arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp),
+				 void *cookie)
+{
+	unsigned long fp, sp, pc;
+
+	fp = (unsigned long)__builtin_frame_address(0);
+	sp = current_stack_pointer;
+	pc = (unsigned long)arch_bpf_stack_walk;
+
+	for (;;) {
+		struct stackframe *frame;
+
+		if (unlikely(!__kernel_text_address(pc)))
+			break;
+		/* pc belongs to the function whose frame pointer is fp */
+		if (!consume_fn(cookie, pc, sp, fp))
+			break;
+		if (unlikely(!fp_is_valid(fp, sp)))
+			break;
+
+		frame = (struct stackframe *)fp - 1;
+		sp = fp;
+		fp = READ_ONCE_TASK_STACK(current, frame->fp);
+		pc = READ_ONCE_TASK_STACK(current, frame->ra);
+	}
+}
+
 #else /* !CONFIG_FRAME_POINTER */
 
 void notrace walk_stackframe(struct task_struct *task,
-- 
2.54.0