Re: [PATCH v2] powerpc/uaccess: Use flexible addressing with __put_user()/__get_user()

[Christophe Leroy]

Le 08/07/2020 à 06:49, Christophe Leroy a écrit :
> Le 07/07/2020 à 21:02, Christophe Leroy a écrit :
> > Le 07/07/2020 à 14:44, Christophe Leroy a écrit :
> > > Le 30/06/2020 à 03:19, Michael Ellerman a écrit :
> > > > Michael Ellerman <mpe@xxxxxxxxxxxxxx> writes:
> > > > > Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
> > > > > > Hi Michael,
> > > > > >
> > > > > > I see this patch is marked as "defered" in patchwork, but I can't see
> > > > > > any related discussion. Is it normal ?
> > > > >
> > > > > Because it uses the "m<>" constraint which didn't work on GCC 4.6.
> > > > >
> > > > > https://github.com/linuxppc/issues/issues/297
> > > > >
> > > > > So we should be able to pick it up for v5.9 hopefully.
> > > >
> > > > It seems to break the build with the kernel.org 4.9.4 compiler and
> > > > corenet64_smp_defconfig:
> > >
> > > Most likely a GCC bug ?
> > >
> > > It seems the problem vanishes with patch 
> > > https://patchwork.ozlabs.org/project/linuxppc-dev/patch/173de3b659fa3a5f126a0eb170522cccd909950f.1594125164.git.christophe.leroy@xxxxxxxxxx/ 
> >
> > Same kind of issue in signal_64.c now.
> >
> > The following patch fixes it: 
> > https://patchwork.ozlabs.org/project/linuxppc-dev/patch/810bd8840ef990a200f58c9dea9abe767ca02a3a.1594146723.git.christophe.leroy@xxxxxxxxxx/ 
>
> This time I confirm, with the two above mentioned patches, it builds OK 
> with 4.9, see 
> http://kisskb.ellerman.id.au/kisskb/head/810bd8840ef990a200f58c9dea9abe767ca02a3a/ 

I see you've merged those patches that make the issue disappear, yet not 
this patch yet. I guess you are still a bit chilly about it, so I split 
it in two parts for you to safely take patch 1 as soon as possible while 
handling the "m<>" constraint subject more carefully via 
https://github.com/linuxppc/issues/issues/297 in a later stage.

Anyway, it seems that GCC doesn't make much use of the "m<>" and the 
pre-update form. Most of the benefit of flexible addressing seems to be 
achieved with patch 1 ie without the "m<>" constraint and update form.

Christophe