linux-kernel - Re: linux-next: Tree for Oct 31 (vboxguest)

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Date:   Thu, 1 Nov 2018 12:32:48 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Changbin Du <changbin.du@...il.com>
Subject: Re: linux-next: Tree for Oct 31 (vboxguest)

Hi Arnd,


On Thu, Nov 1, 2018 at 6:42 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On 10/31/18, Randy Dunlap <rdunlap@...radead.org> wrote:
> > On 10/30/18 8:59 PM, Stephen Rothwell wrote:
> >> Hi all,
> >>
> >> Please do not add any v4.21/v5.1 code to your linux-next included trees
> >> until after the merge window closes.
> >>
> >> Changes since 20181030:
> >>
> >
> >
> > on i386:
> >
> > ld: drivers/virt/vboxguest/vboxguest_core.o: in function
> > `vbg_ioctl_hgcm_call':
> > vboxguest_core.c:(.text+0x212b): undefined reference to `vbg_hgcm_call32'
> >
> >
> > Full randconfig file is attached.
> >
> > Reported-by: Randy Dunlap <rdunlap@...radead.org>
>
> I ran into the same thing, and lots of others like it; they all go back to
> the -Og compiler option introduced in commit 94c7dfd01652 ("kernel
> hacking: support building kernel with -Og optimization level").
>
>
> I have patches for most of these, but I'd prefer if we could leave
> that patch out of 4.20 for now, and have it in linux-next for merging
> into the next merge window, to give us more time to fix up all the
> regressions. This particular instance is fixed by the patch below.


Hmm, I was considering the -Og support for the current MW,
but it might be better to postpone it for 4.21-rc1...



> Other symptoms caused by the change are tons of 'section mismatch'
> warnings for functions that are no longer automatically inlined, and
> sprintf format string overflow warnings when gcc fails to propagate
> an upper bound on an integer argument that is printed into a fixed
> length string.
>
>      Arnd
> ---
> From 8172e650c6797b9cc64c6f7b1c9e5433156290cc Mon Sep 17 00:00:00 2001
> From: Arnd Bergmann <arnd@...db.de>
> Date: Wed, 31 Oct 2018 16:24:35 +0100
> Subject: [PATCH] vbox: fix link error with 'gcc -Og'
>
> With the new CONFIG_CC_OPTIMIZE_FOR_DEBUGGING option, we get a link
> error in the vboxguest driver, when that fails to optimize out the
> call to the compat handler:
>
> drivers/virt/vboxguest/vboxguest_core.o: In function `vbg_ioctl_hgcm_call':
> vboxguest_core.c:(.text+0x1f6e): undefined reference to `vbg_hgcm_call32'
>
> Another compile-time check documents better what we want and avoids
> the error.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>
> diff --git a/drivers/virt/vboxguest/vboxguest_core.c
> b/drivers/virt/vboxguest/vboxguest_core.c
> index 3093655c7b92..1475ed5ffcde 100644
> --- a/drivers/virt/vboxguest/vboxguest_core.c
> +++ b/drivers/virt/vboxguest/vboxguest_core.c
> @@ -1312,7 +1312,7 @@ static int vbg_ioctl_hgcm_call(struct vbg_dev *gdev,
>                 return -EINVAL;
>         }
>
> -       if (f32bit)
> +       if (IS_ENABLED(CONFIG_COMPAT) && f32bit)
>                 ret = vbg_hgcm_call32(gdev, client_id,
>                                       call->function, call->timeout_ms,
>                                       VBG_IOCTL_HGCM_CALL_PARMS32(call),

Right, but adding the CONFIG_COMPAT guard to both the caller and the callee
looks a bit redundant...


I think most cases causing this kind of problem
rely on the assumption that 'static' functions are inlined.

We can force the compiler to do so
by replacing 'static' with 'static __always_inline'


-- 
Best Regards
Masahiro Yamada