On Thu, Sep 15, 2022 at 01:11:11PM +0200, Peter Zijlstra wrote:
> From: Peter Zijlstra <peterz@infradead.org>
> 
> Allow STT_NOTYPE to tail-call into STT_FUNC, per definition STT_NOTYPE
> is not a sub-function of the STT_FUNC.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  tools/objtool/check.c |   29 ++++++++++++++++++++---------
>  1 file changed, 20 insertions(+), 9 deletions(-)
> 
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -1370,6 +1370,16 @@ static void add_return_call(struct objto
>  
>  static bool same_function(struct instruction *insn1, struct instruction *insn2)
>  {
> +	if (!insn1->func && !insn2->func)
> +		return true;
> +
> +	/* Allow STT_NOTYPE -> STT_FUNC+0 tail-calls */
> +	if (!insn1->func && insn1->func != insn2->func)
> +		return false;

Looks like this check is triggering below warning:

vmlinux.o: warning: objtool: ftrace_replace_code.cold+0x0: unreachable instruction

(.config is attached)

> +
> +	if (!insn2->func)
> +		return true;
> +
>  	return insn1->func->pfunc == insn2->func->pfunc;
>  }