[PATCH 32/33] sched: Add __schedule() to stacktool whitelist

[Josh Poimboeuf]

stacktool reports the following warnings for __schedule():

  stacktool: kernel/sched/core.o: __schedule()+0x3c0: duplicate frame pointer save
  stacktool: kernel/sched/core.o: __schedule()+0x3fd: sibling call from callable instruction with changed frame pointer
  stacktool: kernel/sched/core.o: __schedule()+0x40a: call without frame pointer save/setup
  stacktool: kernel/sched/core.o: __schedule()+0x7fd: frame pointer state mismatch
  stacktool: kernel/sched/core.o: __schedule()+0x421: frame pointer state mismatch

Basically it's confused by two unusual attributes of the switch_to()
macro:

1. It saves prev's frame pointer to the old stack and restores next's
   frame pointer from the new stack.

2. For new tasks it jumps directly to ret_from_fork.

Eventually it would probably be a good idea to clean up the
ret_from_fork hack so that new tasks are created with a valid initial
stack, as suggested by Andy:

  https://lkml.kernel.org/r/CALCETrWsqCw4L1qKO9j9L5F+4ED4viuLQTFc=n1pKBZfFPQUFg@xxxxxxxxxxxxxx

Then __schedule() could return normally into the new code and stacktool
hopefully wouldn't have a problem anymore.

In the meantime, add it to the stacktool whitelist so we can have a
baseline with no stacktool warnings.  The marker also serves as a
reminder that this code could be improved a bit.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 kernel/sched/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 474658b..cc7e8e70 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -74,6 +74,7 @@
 #include <linux/binfmts.h>
 #include <linux/context_tracking.h>
 #include <linux/compiler.h>
+#include <linux/stacktool.h>
 
 #include <asm/switch_to.h>
 #include <asm/tlb.h>
@@ -3288,6 +3289,7 @@ static void __sched notrace __schedule(bool preempt)
 
 	balance_callback(rq);
 }
+STACKTOOL_IGNORE_FUNC(__schedule);
 
 static inline void sched_submit_work(struct task_struct *tsk)
 {
-- 
2.4.3