[PATCH v3 5/8] ftrace: Add swap_func to ftrace_process_locs()

[Mike Rapoport <rppt@kernel.org>]

From: Song Liu <song@kernel.org>

ftrace_process_locs sorts module mcount, which is inside RO memory. Add a
ftrace_swap_func so that archs can use RO-memory-poke function to do the
sorting.

Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 include/linux/ftrace.h |  2 ++
 kernel/trace/ftrace.c  | 19 ++++++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index fd5e84d0ec47..b794dcb7cae8 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -1188,4 +1188,6 @@ unsigned long arch_syscall_addr(int nr);
 
 #endif /* CONFIG_FTRACE_SYSCALLS */
 
+void ftrace_swap_func(void *a, void *b, int n);
+
 #endif /* _LINUX_FTRACE_H */
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4c28dd177ca6..95bb9b52ab36 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6989,6 +6989,23 @@ static void test_is_sorted(unsigned long *start, unsigned long count)
 }
 #endif
 
+/*
+ * ftrace_process_locs sorts module mcount, which might be inside RO
+ * memory.
+ * ftrace_swap_func allows architectures to use RO-memory-poke function to
+ * do the sorting.
+ */
+void __weak ftrace_swap_func(void *a, void *b, int n)
+{
+	unsigned long t;
+
+	WARN_ON_ONCE(n != sizeof(t));
+
+	t = *((unsigned long *)a);
+	*(unsigned long *)a = *(unsigned long *)b;
+	*(unsigned long *)b = t;
+}
+
 static int ftrace_process_locs(struct module *mod,
 			       unsigned long *start,
 			       unsigned long *end)
@@ -7016,7 +7033,7 @@ static int ftrace_process_locs(struct module *mod,
 	 */
 	if (!IS_ENABLED(CONFIG_BUILDTIME_MCOUNT_SORT) || mod) {
 		sort(start, count, sizeof(*start),
-		     ftrace_cmp_ips, NULL);
+		     ftrace_cmp_ips, ftrace_swap_func);
 	} else {
 		test_is_sorted(start, count);
 	}
-- 
2.43.0