Re: [PATCH] x86/mem_sharing: silence ubsan warning

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Mon, Jan 4, 2021 at 7:31 AM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> On 03/01/2021 18:47, Tamas K Lengyel wrote:
> > Running Xen compiled with UBSAN produces a warning for mismatched size. It's
> > benign but this patch silences the warning.
> >
> > Signed-off-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> > ---
> >  xen/arch/x86/mm/mem_sharing.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
> > index c428fd16ce..6920077dbf 100644
> > --- a/xen/arch/x86/mm/mem_sharing.c
> > +++ b/xen/arch/x86/mm/mem_sharing.c
> > @@ -1638,7 +1638,10 @@ static int fork_hap_allocation(struct domain *cd, 
> > struct domain *d)
> >      rc = hap_set_allocation(cd, mb << (20 - PAGE_SHIFT), &preempted);
> >      paging_unlock(cd);
> >
> > -    return preempted ? -ERESTART : rc;
> > +    if ( preempted )
> > +        rc = -ERESTART;
> > +
> > +    return rc;
>
> I can't repro this at all, even with some simplified examples.
>
> -ERESTART is int (it is an enum constant in C files), as is rc, so I
> can't spot a legitimate UBSAN complaint here.
>
> Which compiler, and/or do you have the exact complaint available?

It was with gcc-7 on debian buster but can't recreate it after a make
clean & make, it's now gone ¯\_(ツ)_/¯, seems like it was just a bad
build. Sorry for the noise.

Tamas