1 files changed, 110 insertions, 0 deletions
diff --git a/arch/loongarch/kernel/ftrace_dyn.c b/arch/loongarch/kernel/ftrace_dyn.c
new file mode 100644
index 000000000000..3b82bface840
--- /dev/null
+++ b/arch/loongarch/kernel/ftrace_dyn.c
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Based on arch/arm64/kernel/ftrace.c
+ *
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+
+#include <linux/ftrace.h>
+#include <linux/uaccess.h>
+
+#include <asm/inst.h>
+
+static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, bool validate)
+{
+	u32 replaced;
+
+	if (validate) {
+		if (larch_insn_read((void *)pc, &replaced))
+			return -EFAULT;
+
+		if (replaced != old)
+			return -EINVAL;
+	}
+
+	if (larch_insn_patch_text((void *)pc, new))
+		return -EPERM;
+
+	return 0;
+}
+
+int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+	u32 new;
+	unsigned long pc;
+
+	pc = (unsigned long)&ftrace_call;
+	new = larch_insn_gen_bl(pc, (unsigned long)func);
+
+	return ftrace_modify_code(pc, 0, new, false);
+}
+
+/*
+ * The compiler has inserted 2 NOPs before the regular function prologue.
+ * T series registers are available and safe because of LoongArch's psABI.
+ *
+ * At runtime, we can replace nop with bl to enable ftrace call and replace bl
+ * with nop to disable ftrace call. The bl requires us to save the original RA
+ * value, so it saves RA at t0 here.
+ *
+ * Details are:
+ *
+ * | Compiled   |       Disabled         |        Enabled         |
+ * +------------+------------------------+------------------------+
+ * | nop        | move     t0, ra        | move     t0, ra        |
+ * | nop        | nop                    | bl       ftrace_caller |
+ * | func_body  | func_body              | func_body              |
+ *
+ * The RA value will be recovered by ftrace_regs_entry, and restored into RA
+ * before returning to the regular function prologue. When a function is not
+ * being traced, the "move t0, ra" is not harmful.
+ */
+
+int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
+{
+	u32 old, new;
+	unsigned long pc;
+
+	pc = rec->ip;
+	old = larch_insn_gen_nop();
+	new = larch_insn_gen_move(LOONGARCH_GPR_T0, LOONGARCH_GPR_RA);
+
+	return ftrace_modify_code(pc, old, new, true);
+}
+
+int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+{
+	u32 old, new;
+	unsigned long pc;
+
+	pc = rec->ip + LOONGARCH_INSN_SIZE;
+
+	old = larch_insn_gen_nop();
+	new = larch_insn_gen_bl(pc, addr);
+
+	return ftrace_modify_code(pc, old, new, true);
+}
+
+int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
+{
+	u32 old, new;
+	unsigned long pc;
+
+	pc = rec->ip + LOONGARCH_INSN_SIZE;
+
+	new = larch_insn_gen_nop();
+	old = larch_insn_gen_bl(pc, addr);
+
+	return ftrace_modify_code(pc, old, new, true);
+}
+
+void arch_ftrace_update_code(int command)
+{
+	command |= FTRACE_MAY_SLEEP;
+	ftrace_modify_all_code(command);
+}
+
+int __init ftrace_dyn_arch_init(void)
+{
+	return 0;
+}