ftrace: Allow archs to specify if they need a separate function graph trampoline

Currently if an arch supports function graph tracing, the core code will
just assign the function graph trampoline to the function graph addr that
gets called.

But as the old method for function graph tracing always calls the function
trampoline first and that calls the function graph trampoline, some
archs may have the function graph trampoline dependent on operations that
were done in the function trampoline. This causes function graph tracer
to break on those archs.

Instead of having the default be to set the function graph ftrace_ops
to the function graph trampoline, have it instead just set it to zero
which will keep it from jumping to a trampoline that is not set up
to be jumped directly too.

Link: http://lkml.kernel.org/r/53BED155.9040607@nvidia.com

Reported-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Tested-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 45aac1a742c5..1776153ea6e0 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5366,7 +5366,8 @@ int register_ftrace_graph(trace_func_graph_ret_t retfunc,
 
 #ifdef CONFIG_DYNAMIC_FTRACE
         /* Optimize function graph calling (if implemented by arch) */
-        global_ops.trampoline = FTRACE_GRAPH_ADDR;
+        if (FTRACE_GRAPH_TRAMP_ADDR != 0)
+                global_ops.trampoline = FTRACE_GRAPH_TRAMP_ADDR;
 #endif
 
         ret = ftrace_startup(&global_ops, FTRACE_START_FUNC_RET);
@@ -5390,7 +5391,8 @@ void unregister_ftrace_graph(void)
         ftrace_shutdown(&global_ops, FTRACE_STOP_FUNC_RET);
         global_ops.flags &= ~FTRACE_OPS_FL_STUB;
 #ifdef CONFIG_DYNAMIC_FTRACE
-        global_ops.trampoline = 0;
+        if (FTRACE_GRAPH_TRAMP_ADDR != 0)
+                global_ops.trampoline = 0;
 #endif
         unregister_pm_notifier(&ftrace_suspend_notifier);
         unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);