v4.19.13 snapshot.
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
new file mode 100644
index 0000000..c433f6d
--- /dev/null
+++ b/arch/riscv/kernel/ftrace.c
@@ -0,0 +1,202 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2013 Linaro Limited
+ * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
+ * Copyright (C) 2017 Andes Technology Corporation
+ */
+
+#include <linux/ftrace.h>
+#include <linux/uaccess.h>
+#include <asm/cacheflush.h>
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+static int ftrace_check_current_call(unsigned long hook_pos,
+ unsigned int *expected)
+{
+ unsigned int replaced[2];
+ unsigned int nops[2] = {NOP4, NOP4};
+
+ /* we expect nops at the hook position */
+ if (!expected)
+ expected = nops;
+
+ /*
+ * Read the text we want to modify;
+ * return must be -EFAULT on read error
+ */
+ if (probe_kernel_read(replaced, (void *)hook_pos, MCOUNT_INSN_SIZE))
+ return -EFAULT;
+
+ /*
+ * Make sure it is what we expect it to be;
+ * return must be -EINVAL on failed comparison
+ */
+ if (memcmp(expected, replaced, sizeof(replaced))) {
+ pr_err("%p: expected (%08x %08x) but get (%08x %08x)",
+ (void *)hook_pos, expected[0], expected[1], replaced[0],
+ replaced[1]);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
+ bool enable)
+{
+ unsigned int call[2];
+ unsigned int nops[2] = {NOP4, NOP4};
+ int ret = 0;
+
+ make_call(hook_pos, target, call);
+
+ /* replace the auipc-jalr pair at once */
+ ret = probe_kernel_write((void *)hook_pos, enable ? call : nops,
+ MCOUNT_INSN_SIZE);
+ /* return must be -EPERM on write error */
+ if (ret)
+ return -EPERM;
+
+ smp_mb();
+ flush_icache_range((void *)hook_pos, (void *)hook_pos + MCOUNT_INSN_SIZE);
+
+ return 0;
+}
+
+int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+{
+ int ret = ftrace_check_current_call(rec->ip, NULL);
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call(rec->ip, addr, true);
+}
+
+int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
+ unsigned long addr)
+{
+ unsigned int call[2];
+ int ret;
+
+ make_call(rec->ip, addr, call);
+ ret = ftrace_check_current_call(rec->ip, call);
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call(rec->ip, addr, false);
+}
+
+int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+ int ret = __ftrace_modify_call((unsigned long)&ftrace_call,
+ (unsigned long)func, true);
+ if (!ret) {
+ ret = __ftrace_modify_call((unsigned long)&ftrace_regs_call,
+ (unsigned long)func, true);
+ }
+
+ return ret;
+}
+
+int __init ftrace_dyn_arch_init(void)
+{
+ return 0;
+}
+#endif
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+ unsigned long addr)
+{
+ unsigned int call[2];
+ int ret;
+
+ make_call(rec->ip, old_addr, call);
+ ret = ftrace_check_current_call(rec->ip, call);
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call(rec->ip, addr, true);
+}
+#endif
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+/*
+ * Most of this function is copied from arm64.
+ */
+void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
+ unsigned long frame_pointer)
+{
+ unsigned long return_hooker = (unsigned long)&return_to_handler;
+ unsigned long old;
+ int err;
+
+ if (unlikely(atomic_read(¤t->tracing_graph_pause)))
+ return;
+
+ /*
+ * We don't suffer access faults, so no extra fault-recovery assembly
+ * is needed here.
+ */
+ old = *parent;
+
+ if (function_graph_enter(old, self_addr, frame_pointer, parent))
+ *parent = return_hooker;
+}
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+extern void ftrace_graph_call(void);
+int ftrace_enable_ftrace_graph_caller(void)
+{
+ unsigned int call[2];
+ static int init_graph = 1;
+ int ret;
+
+ make_call(&ftrace_graph_call, &ftrace_stub, call);
+
+ /*
+ * When enabling graph tracer for the first time, ftrace_graph_call
+ * should contains a call to ftrace_stub. Once it has been disabled,
+ * the 8-bytes at the position becomes NOPs.
+ */
+ if (init_graph) {
+ ret = ftrace_check_current_call((unsigned long)&ftrace_graph_call,
+ call);
+ init_graph = 0;
+ } else {
+ ret = ftrace_check_current_call((unsigned long)&ftrace_graph_call,
+ NULL);
+ }
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call((unsigned long)&ftrace_graph_call,
+ (unsigned long)&prepare_ftrace_return, true);
+}
+
+int ftrace_disable_ftrace_graph_caller(void)
+{
+ unsigned int call[2];
+ int ret;
+
+ make_call(&ftrace_graph_call, &prepare_ftrace_return, call);
+
+ /*
+ * This is to make sure that ftrace_enable_ftrace_graph_caller
+ * did the right thing.
+ */
+ ret = ftrace_check_current_call((unsigned long)&ftrace_graph_call,
+ call);
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call((unsigned long)&ftrace_graph_call,
+ (unsigned long)&prepare_ftrace_return, false);
+}
+#endif /* CONFIG_DYNAMIC_FTRACE */
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */