v4.19.13 snapshot.
diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c
new file mode 100644
index 0000000..4f0e17b
--- /dev/null
+++ b/arch/x86/kernel/unwind_guess.c
@@ -0,0 +1,72 @@
+#include <linux/sched.h>
+#include <linux/ftrace.h>
+#include <asm/ptrace.h>
+#include <asm/bitops.h>
+#include <asm/stacktrace.h>
+#include <asm/unwind.h>
+
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+ unsigned long addr;
+
+ if (unwind_done(state))
+ return 0;
+
+ addr = READ_ONCE_NOCHECK(*state->sp);
+
+ return ftrace_graph_ret_addr(state->task, &state->graph_idx,
+ addr, state->sp);
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+{
+ return NULL;
+}
+
+bool unwind_next_frame(struct unwind_state *state)
+{
+ struct stack_info *info = &state->stack_info;
+
+ if (unwind_done(state))
+ return false;
+
+ do {
+ for (state->sp++; state->sp < info->end; state->sp++) {
+ unsigned long addr = READ_ONCE_NOCHECK(*state->sp);
+
+ if (__kernel_text_address(addr))
+ return true;
+ }
+
+ state->sp = PTR_ALIGN(info->next_sp, sizeof(long));
+
+ } while (!get_stack_info(state->sp, state->task, info,
+ &state->stack_mask));
+
+ return false;
+}
+EXPORT_SYMBOL_GPL(unwind_next_frame);
+
+void __unwind_start(struct unwind_state *state, struct task_struct *task,
+ struct pt_regs *regs, unsigned long *first_frame)
+{
+ memset(state, 0, sizeof(*state));
+
+ state->task = task;
+ state->sp = PTR_ALIGN(first_frame, sizeof(long));
+
+ get_stack_info(first_frame, state->task, &state->stack_info,
+ &state->stack_mask);
+
+ /*
+ * The caller can provide the address of the first frame directly
+ * (first_frame) or indirectly (regs->sp) to indicate which stack frame
+ * to start unwinding at. Skip ahead until we reach it.
+ */
+ if (!unwind_done(state) &&
+ (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
+ !__kernel_text_address(*first_frame)))
+ unwind_next_frame(state);
+}
+EXPORT_SYMBOL_GPL(__unwind_start);