v4.19.13 snapshot.
diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
new file mode 100644
index 0000000..a56e7c8
--- /dev/null
+++ b/arch/arm/kernel/stacktrace.c
@@ -0,0 +1,171 @@
+#include <linux/export.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/stacktrace.h>
+
+#include <asm/sections.h>
+#include <asm/stacktrace.h>
+#include <asm/traps.h>
+
+#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
+/*
+ * Unwind the current stack frame and store the new register values in the
+ * structure passed as argument. Unwinding is equivalent to a function return,
+ * hence the new PC value rather than LR should be used for backtrace.
+ *
+ * With framepointer enabled, a simple function prologue looks like this:
+ * mov ip, sp
+ * stmdb sp!, {fp, ip, lr, pc}
+ * sub fp, ip, #4
+ *
+ * A simple function epilogue looks like this:
+ * ldm sp, {fp, sp, pc}
+ *
+ * Note that with framepointer enabled, even the leaf functions have the same
+ * prologue and epilogue, therefore we can ignore the LR value in this case.
+ */
+int notrace unwind_frame(struct stackframe *frame)
+{
+ unsigned long high, low;
+ unsigned long fp = frame->fp;
+
+ /* only go to a higher address on the stack */
+ low = frame->sp;
+ high = ALIGN(low, THREAD_SIZE);
+
+ /* check current frame pointer is within bounds */
+ if (fp < low + 12 || fp > high - 4)
+ return -EINVAL;
+
+ /* restore the registers from the stack frame */
+ frame->fp = *(unsigned long *)(fp - 12);
+ frame->sp = *(unsigned long *)(fp - 8);
+ frame->pc = *(unsigned long *)(fp - 4);
+
+ return 0;
+}
+#endif
+
+void notrace walk_stackframe(struct stackframe *frame,
+ int (*fn)(struct stackframe *, void *), void *data)
+{
+ while (1) {
+ int ret;
+
+ if (fn(frame, data))
+ break;
+ ret = unwind_frame(frame);
+ if (ret < 0)
+ break;
+ }
+}
+EXPORT_SYMBOL(walk_stackframe);
+
+#ifdef CONFIG_STACKTRACE
+struct stack_trace_data {
+ struct stack_trace *trace;
+ unsigned int no_sched_functions;
+ unsigned int skip;
+};
+
+static int save_trace(struct stackframe *frame, void *d)
+{
+ struct stack_trace_data *data = d;
+ struct stack_trace *trace = data->trace;
+ struct pt_regs *regs;
+ unsigned long addr = frame->pc;
+
+ if (data->no_sched_functions && in_sched_functions(addr))
+ return 0;
+ if (data->skip) {
+ data->skip--;
+ return 0;
+ }
+
+ trace->entries[trace->nr_entries++] = addr;
+
+ if (trace->nr_entries >= trace->max_entries)
+ return 1;
+
+ if (!in_entry_text(frame->pc))
+ return 0;
+
+ regs = (struct pt_regs *)frame->sp;
+
+ trace->entries[trace->nr_entries++] = regs->ARM_pc;
+
+ return trace->nr_entries >= trace->max_entries;
+}
+
+/* This must be noinline to so that our skip calculation works correctly */
+static noinline void __save_stack_trace(struct task_struct *tsk,
+ struct stack_trace *trace, unsigned int nosched)
+{
+ struct stack_trace_data data;
+ struct stackframe frame;
+
+ data.trace = trace;
+ data.skip = trace->skip;
+ data.no_sched_functions = nosched;
+
+ if (tsk != current) {
+#ifdef CONFIG_SMP
+ /*
+ * What guarantees do we have here that 'tsk' is not
+ * running on another CPU? For now, ignore it as we
+ * can't guarantee we won't explode.
+ */
+ if (trace->nr_entries < trace->max_entries)
+ trace->entries[trace->nr_entries++] = ULONG_MAX;
+ return;
+#else
+ frame.fp = thread_saved_fp(tsk);
+ frame.sp = thread_saved_sp(tsk);
+ frame.lr = 0; /* recovered from the stack */
+ frame.pc = thread_saved_pc(tsk);
+#endif
+ } else {
+ /* We don't want this function nor the caller */
+ data.skip += 2;
+ frame.fp = (unsigned long)__builtin_frame_address(0);
+ frame.sp = current_stack_pointer;
+ frame.lr = (unsigned long)__builtin_return_address(0);
+ frame.pc = (unsigned long)__save_stack_trace;
+ }
+
+ walk_stackframe(&frame, save_trace, &data);
+ if (trace->nr_entries < trace->max_entries)
+ trace->entries[trace->nr_entries++] = ULONG_MAX;
+}
+
+void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
+{
+ struct stack_trace_data data;
+ struct stackframe frame;
+
+ data.trace = trace;
+ data.skip = trace->skip;
+ data.no_sched_functions = 0;
+
+ frame.fp = regs->ARM_fp;
+ frame.sp = regs->ARM_sp;
+ frame.lr = regs->ARM_lr;
+ frame.pc = regs->ARM_pc;
+
+ walk_stackframe(&frame, save_trace, &data);
+ if (trace->nr_entries < trace->max_entries)
+ trace->entries[trace->nr_entries++] = ULONG_MAX;
+}
+
+void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
+{
+ __save_stack_trace(tsk, trace, 1);
+}
+EXPORT_SYMBOL(save_stack_trace_tsk);
+
+void save_stack_trace(struct stack_trace *trace)
+{
+ __save_stack_trace(current, trace, 0);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace);
+#endif