sched: Mark __schedule() stack frame as non-standard

objtool reports the following warnings for __schedule():

  kernel/sched/core.o: warning: objtool:__schedule()+0x3c0: duplicate frame pointer save
  kernel/sched/core.o: warning: objtool:__schedule()+0x3fd: sibling call from callable instruction with changed frame pointer
  kernel/sched/core.o: warning: objtool:__schedule()+0x40a: call without frame pointer save/setup
  kernel/sched/core.o: warning: objtool:__schedule()+0x7fd: frame pointer state mismatch
  kernel/sched/core.o: warning: objtool:__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@mail.gmail.com

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

In the meantime, mark its stack frame as non-standard so we can have a
baseline with no objtool warnings.  The marker also serves as a reminder
that this code could be improved a bit.

Signed-off-by: Josh Poimboeuf <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Bernd Petrovitsch <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Chris J Arges <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Michal Marek <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Pedro Alves <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/91190e324ebd7fcd01748d508d0dfd4693e84d91.1456719558.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions