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With some configs, objtool reports the following warning: arch/x86/kernel/ftrace.o: warning: objtool: ftrace_modify_code_direct()+0x2d: sibling call from callable instruction with modified stack frame The instruction it's complaining about isn't actually a sibling call. It's just a normal jump to an address inside the function. Objtool thought it was a sibling call because the instruction's jump_dest wasn't initialized because the function was supposed to be ignored due to its use of sync_core(). Objtool ended up validating the function instead of ignoring it because it didn't properly recognize a sibling call to the function. So fix the sibling call logic. Also add a warning to catch ignored functions being validated so we'll get a more useful error message next time. Reported-by: Mike Galbraith <[email protected]> Signed-off-by: Josh Poimboeuf <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/96cc8ecbcdd8cb29ddd783817b4af918a6a171b0.1499437107.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <[email protected]>