linux-kernel - Re: An objtool warning from mainline

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Date:   Thu, 27 Apr 2023 09:55:41 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     jpoimboe@...nel.org, peterz@...radead.org,
        linux-kernel@...r.kernel.org
Subject: Re: An objtool warning from mainline

On Thu, Apr 27, 2023 at 11:14:21AM +0200, Borislav Petkov wrote:
> On Wed, Apr 26, 2023 at 04:50:49PM -0700, Paul E. McKenney wrote:
> > vmlinux.o: warning: objtool: exc_nmi+0x2b3: call to __const_udelay() leaves .noinstr.text section
> 
> What does
> 
> ./scripts/faddr2line vmlinux.o exc_nmi+0x2b3
> 
> say?

$ ./scripts/faddr2line vmlinux.o exc_nmi+0x2b3
exc_nmi+0x2b3/0x3c0:
exc_nmi at ??:?

Which might mean something to you, but does not look all that helpful
to me.  :-/

> I guess it should point to io_check_error()'s udelay().
> 
> If so, it is noinline:
> 
> 81423c37415f ("x86/timer: Don't inline __const_udelay()")

I do have that commit, so it is noinline.

> > I see this with gcc version 11.3.0 (Ubuntu 11.3.0-1ubuntu1~22.04) and also with
> > gcc version 8.5.0 20210514 (Red Hat 8.5.0-18) (GCC).
> 
> I can't trigger it here with
> 
> gcc-11 (Debian 11.2.0-19) 11.2.0
> 
> Which is weird because the asm looks like it should warn.
> 
> Does it go away if you remove the noinline before __const_udelay()?

It stays.

No idea here.

							Thanx, Paul