linux-kernel - Re: [RFC][PATCH][REGRESSION FIX] x86/ftrace: Add ORC annotation to 64 bit ftrace assembly

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Message-ID: <20171223005145.5f4d3884@gandalf.local.home>
Date:   Sat, 23 Dec 2017 00:51:45 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC][PATCH][REGRESSION FIX] x86/ftrace: Add ORC annotation to
 64 bit ftrace assembly

On Fri, 22 Dec 2017 20:43:37 -0600
Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> Objtool doesn't like the fact that save_mcount_regs pushes rbp at the
> beginning, but it's never restored (directly, at least).
> 
> How about something like this instead, where it skips the original rbp
> push?  I didn't test it, but I think it should work.  It at least gets
> rid of the warnings and doesn't need any unwind hints other than the
> UNWIND_HINT_EMPTY in return_to_handler.

There's a reason I did it that way, but don't remember exactly why. I
think we discussed this a while ago when we had issues with ftrace.S
during your first iterations of objtool.

I'll have to test all different compile options and different gcc
compiler versions.

-- Steve