[for-next][PATCH 11/31] ftrace: Add test to make sure compiled time sorts work

From: Steven Rostedt
Date: Tue Jan 11 2022 - 12:31:58 EST


From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>

Now that ftrace function pointers are sorted at compile time, add a test
that makes sure they are sorted at run time. This test is only run if it is
configured in.

Link: https://lkml.kernel.org/r/20211206151858.4d21a24d@xxxxxxxxxxxxxxxxxx

Cc: Yinan Liu <yinan@xxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
kernel/trace/Kconfig | 14 ++++++++++++++
kernel/trace/ftrace.c | 23 +++++++++++++++++++++++
2 files changed, 37 insertions(+)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 420ff4bc67fd..f468767bc287 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -915,6 +915,20 @@ config EVENT_TRACE_TEST_SYSCALLS
TBD - enable a way to actually call the syscalls as we test their
events

+config FTRACE_SORT_STARTUP_TEST
+ bool "Verify compile time sorting of ftrace functions"
+ depends on DYNAMIC_FTRACE
+ depends on BUILDTIME_TABLE_SORT
+ help
+ Sorting of the mcount_loc sections that is used to find the
+ where the ftrace knows where to patch functions for tracing
+ and other callbacks is done at compile time. But if the sort
+ is not done correctly, it will cause non-deterministic failures.
+ When this is set, the sorted sections will be verified that they
+ are in deed sorted and will warn if they are not.
+
+ If unsure, say N
+
config RING_BUFFER_STARTUP_TEST
bool "Ring buffer startup self test"
depends on RING_BUFFER
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 9ca63df6553a..403e485bf091 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6388,6 +6388,27 @@ static int ftrace_cmp_ips(const void *a, const void *b)
return 0;
}

+#ifdef CONFIG_FTRACE_SORT_STARTUP_TEST
+static void test_is_sorted(unsigned long *start, unsigned long count)
+{
+ int i;
+
+ for (i = 1; i < count; i++) {
+ if (WARN(start[i - 1] > start[i],
+ "[%d] %pS at %lx is not sorted with %pS at %lx\n", i,
+ (void *)start[i - 1], start[i - 1],
+ (void *)start[i], start[i]))
+ break;
+ }
+ if (i == count)
+ pr_info("ftrace section at %px sorted properly\n", start);
+}
+#else
+static void test_is_sorted(unsigned long *start, unsigned long count)
+{
+}
+#endif
+
static int ftrace_process_locs(struct module *mod,
unsigned long *start,
unsigned long *end)
@@ -6414,6 +6435,8 @@ static int ftrace_process_locs(struct module *mod,
if (!IS_ENABLED(CONFIG_BUILDTIME_TABLE_SORT) || mod) {
sort(start, count, sizeof(*start),
ftrace_cmp_ips, NULL);
+ } else {
+ test_is_sorted(start, count);
}

start_pg = ftrace_allocate_pages(count);
--
2.33.0