ftrace: Add variable ftrace_expected for archs to show expected code

When an anomaly is found while modifying function code, ftrace_bug() is
called which disables the function tracing infrastructure and reports
information about what failed. If the code that is to be replaced does not
match what is expected, then actual code is shown. Currently there is no
arch generic way to show what was expected.

Add a new variable pointer calld ftrace_expected that the arch code can set
to point to what it expected so that ftrace_bug() can report the actual text
as well as the text that was expected to be there.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index b95efcac9dfe..7870c03b4c4d 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1940,7 +1940,7 @@ static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
 	return __ftrace_hash_update_ipmodify(ops, old_hash, new_hash);
 }
 
-static void print_ip_ins(const char *fmt, unsigned char *p)
+static void print_ip_ins(const char *fmt, const unsigned char *p)
 {
 	int i;
 
@@ -1954,6 +1954,7 @@ static struct ftrace_ops *
 ftrace_find_tramp_ops_any(struct dyn_ftrace *rec);
 
 enum ftrace_bug_type ftrace_bug_type;
+const void *ftrace_expected;
 
 static void print_bug_type(void)
 {
@@ -2001,8 +2002,12 @@ void ftrace_bug(int failed, struct dyn_ftrace *rec)
 		FTRACE_WARN_ON_ONCE(1);
 		pr_info("ftrace failed to modify ");
 		print_ip_sym(ip);
-		print_ip_ins(" actual: ", (unsigned char *)ip);
+		print_ip_ins(" actual:   ", (unsigned char *)ip);
 		pr_cont("\n");
+		if (ftrace_expected) {
+			print_ip_ins(" expected: ", ftrace_expected);
+			pr_cont("\n");
+		}
 		break;
 	case -EPERM:
 		FTRACE_WARN_ON_ONCE(1);