riscv/ftrace: Add dynamic function tracer support

We now have dynamic ftrace with the following added items:

* ftrace_make_call, ftrace_make_nop (in kernel/ftrace.c)
  The two functions turn each recorded call site of filtered functions
  into a call to ftrace_caller or nops

* ftracce_update_ftrace_func (in kernel/ftrace.c)
  turns the nops at ftrace_call into a call to a generic entry for
  function tracers.

* ftrace_caller (in kernel/mcount-dyn.S)
  The entry where each _mcount call sites calls to once they are
  filtered to be traced.

Also, this patch fixes the semantic problems in mcount.S, which will be
treated as only a reference implementation once we have the dynamic
ftrace.

Cc: Greentime Hu <greentime@andestech.com>
Signed-off-by: Alan Kao <alankao@andestech.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

1 files changed, 102 insertions, 1 deletions

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index d0de68d144cb..be4b24332d97 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -6,9 +6,109 @@
  */
 
 #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_FUNCTION_GRAPH_TRACER
 /*
- * Most of this file is copied from arm64.
+ * Most of this function is copied from arm64.
  */
 void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 			   unsigned long frame_pointer)
@@ -39,3 +139,4 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
 		return;
 	*parent = return_hooker;
 }
+#endif