[for-linus][PATCH 2/7] tracing: Define MCOUNT_INSN_SIZE when not defined without direct calls

From: Steven Rostedt
Date: Mon Jan 06 2020 - 16:20:20 EST

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

In order to handle direct calls along side of function graph tracer, a check
is made to see if the address being traced by the function graph tracer is a
direct call or not. To get the address used by direct callers, the return
address is subtracted by MCOUNT_INSN_SIZE.

For some archs with certain configurations, MCOUNT_INSN_SIZE is undefined
here. But these should not be using direct calls anyway. Just define
MCOUNT_INSN_SIZE to zero in this case.

Link: https://lore.kernel.org/r/202001020219.zvE3vsty%lkp@xxxxxxxxx

Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Fixes: ff205766dbbee ("ftrace: Fix function_graph tracer interaction with BPF trampoline")
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
kernel/trace/fgraph.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index a2659735db73..1af321dec0f1 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -96,6 +96,20 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func,
return 0;

+ * Not all archs define MCOUNT_INSN_SIZE which is used to look for direct
+ * functions. But those archs currently don't support direct functions
+ * anyway, and ftrace_find_rec_direct() is just a stub for them.
+ * Define MCOUNT_INSN_SIZE to keep those archs compiling.
+ */
+/* Make sure this only works without direct calls */
+# error MCOUNT_INSN_SIZE not defined with direct calls enabled
+# endif
+# define MCOUNT_INSN_SIZE 0
int function_graph_enter(unsigned long ret, unsigned long func,
unsigned long frame_pointer, unsigned long *retp)