ftrace, orc, x86: Handle ftrace dynamically allocated trampolines

The function tracer can create a dynamically allocated trampoline that is
called by the function mcount or fentry hook that is used to call the
function callback that is registered. The problem is that the orc undwinder
will bail if it encounters one of these trampolines. This breaks the stack
trace of function callbacks, which include the stack tracer and setting the
stack trace for individual functions.

Since these dynamic trampolines are basically copies of the static ftrace
trampolines defined in ftrace_*.S, we do not need to create new orc entries
for the dynamic trampolines. Finding the return address on the stack will be
identical as the functions that were copied to create the dynamic
trampolines. When encountering a ftrace dynamic trampoline, we can just use
the orc entry of the ftrace static function that was copied for that
trampoline.

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

1 files changed, 17 insertions, 12 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index ccdf3664e4a9..554b517c61a0 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1119,15 +1119,11 @@ static struct ftrace_ops global_ops = {
 };
 
 /*
- * This is used by __kernel_text_address() to return true if the
- * address is on a dynamically allocated trampoline that would
- * not return true for either core_kernel_text() or
- * is_module_text_address().
+ * Used by the stack undwinder to know about dynamic ftrace trampolines.
  */
-bool is_ftrace_trampoline(unsigned long addr)
+struct ftrace_ops *ftrace_ops_trampoline(unsigned long addr)
 {
-        struct ftrace_ops *op;
-        bool ret = false;
+        struct ftrace_ops *op = NULL;
 
         /*
          * Some of the ops may be dynamically allocated,
@@ -1144,15 +1140,24 @@ bool is_ftrace_trampoline(unsigned long addr)
                 if (op->trampoline && op->trampoline_size)
                         if (addr >= op->trampoline &&
                             addr < op->trampoline + op->trampoline_size) {
-                                ret = true;
-                                goto out;
+                                preempt_enable_notrace();
+                                return op;
                         }
         } while_for_each_ftrace_op(op);
-
- out:
         preempt_enable_notrace();
 
-        return ret;
+        return NULL;
+}
+
+/*
+ * This is used by __kernel_text_address() to return true if the
+ * address is on a dynamically allocated trampoline that would
+ * not return true for either core_kernel_text() or
+ * is_module_text_address().
+ */
+bool is_ftrace_trampoline(unsigned long addr)
+{
+        return ftrace_ops_trampoline(addr) != NULL;
 }
 
 struct ftrace_page {