[PATCH v3] ftrace: Hide a extra entry in stack trace

From: Tatsuya S
Date: Wed Oct 02 2024 - 01:16:41 EST


A extra entry is shown on stack trace(CONFIG_UNWINDER_ORC=y).

[003] ..... 110.171589: vfs_write <-__x64_sys_write
[003] ..... 110.171600: <stack trace>
=> XXXXXXXXX (Wrong function name)
=> vfs_write
=> ksys_write
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe

To resolve this, increment skip for __ftrace_trace_stack() in
function_stack_trace_call().
The reason why skip is incremented for __ftrace_trace_stack()
is because __ftrace_trace_stack() in stack trace is the only function
that wasn't skipped from anywhere.

Signed-off-by: Tatsuya S <tatsuya.s2862@xxxxxxxxx>
---
V2 -> V3: Changed the place to increment skip number
V1 -> V2: Fixed redundant code

kernel/trace/trace_functions.c | 24 +++++++++++-------------
1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 3b0cea37e029..27089d8e65d4 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -203,23 +203,21 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
ftrace_test_recursion_unlock(bit);
}

-#ifdef CONFIG_UNWINDER_ORC
-/*
- * Skip 2:
- *
- * function_stack_trace_call()
- * ftrace_call()
- */
-#define STACK_SKIP 2
-#else
/*
* Skip 3:
- * __trace_stack()
- * function_stack_trace_call()
- * ftrace_call()
+ * Skipped functions if CONFIG_UNWINDER_ORC is defined
+ *
+ * __ftrace_trace_stack()
+ * function_stack_trace_call()
+ * ftrace_call()
+ *
+ * Otherwise
+ *
+ * __trace_stack()
+ * function_stack_trace_call()
+ * ftrace_call()
*/
#define STACK_SKIP 3
-#endif

static void
function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
--
2.46.2