linux-kernel - Re: [PATCH v2 6/8] x86/entry: add unwind hint annotations

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Date:   Fri, 30 Jun 2017 10:55:00 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        live-patching@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Slaby <jslaby@...e.cz>, Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mike Galbraith <efault@....de>
Subject: Re: [PATCH v2 6/8] x86/entry: add unwind hint annotations

On Fri, Jun 30, 2017 at 08:44:40AM -0700, Andy Lutomirski wrote:
> > A few comments about the first patch:
> >
> >   https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_irq_stack&id=3e2aa2102cc1c5e60d4a8637bff78d0478a55059
> >
> > - It uses a '693:' label instead of '.Lirqs_off_\@:'
> 
> Touché!
> 
> >
> > - There's a comment I don't follow:
> >
> >     "Anything that can interrupt us here without using IST must be
> >     *extremely* careful to limit its stack usage."
> >
> >   What specifically could interrupt there without using IST?
> 
> #DB, later on in the series.  I'll update the comment.
> 
> >
> > - Since do_softirq_own_stack() is a callable function, I think it still
> >   needs to save rbp.
> 
> Whoops.
> 
> >
> > - Why change the "jmp error_exit" to "ret" in
> >   xen_do_hypervisor_callback()?
> 
> To match the other change I made there.  I removed both.

One more thing I forgot to mention: if you could use r10 instead of r11,
that would be helpful because it means one less register undwarf needs
to know about.  (It already deals with r10 because of GCC stack
realignment).

-- 
Josh