On Mon, Nov 16, 2020 at 12:45:41PM +0100, Martin Kletzander wrote:
> On Mon, Nov 16, 2020 at 10:48:20AM +0000, Daniel P. Berrangé wrote:
> > On Mon, Nov 16, 2020 at 11:26:45AM +0100, Michal Privoznik wrote:
> > > On 11/16/20 10:59 AM, Daniel P. Berrangé wrote:
> > > > On Mon, Nov 16, 2020 at 10:52:54AM +0100, Martin Kletzander wrote:
> > > > > On Mon, Nov 16, 2020 at 09:24:22AM +0000, Daniel P. Berrangé wrote:
> > > > > > On Sun, Nov 15, 2020 at 09:42:40PM +0100, Martin Kletzander wrote:
> > > > > > > This reverts commit b3710e9a2af402a2b620de570b062294e11190eb.
> > > > > > >
> > > > > > > That check is very valuable for our code, but it causes issue with glib >=
> > > > > > > 2.67.0 when building with clang.
> > > > > > >
> > > > > > > The reason is a combination of two commits in glib, firstly fdda405b6b1b which
> > > > > > > adds a g_atomic_pointer_{set,get} variants that enforce stricter type
> > > > > > > checking (by removing an extra cast) for compilers that support __typeof__, and
> > > > > > > commit dce24dc4492d which effectively enabled the new variant of glib's atomic
> > > > > > > code for clang. This will not be necessary when glib's issue #600 [0] (8 years
> > > > > > > old) is fixed. Thankfully, MR #1719 [1], which is supposed to deal with this
> > > > > > > issue was opened 3 weeks ago, so there is a slight sliver of hope.
> > > > > > >
> > > > > > > [0] https://gitlab.gnome.org/GNOME/glib/-/issues/600
> > > > > > > [1] https://gitlab.gnome.org/GNOME/glib/-/merge_requests/1719
> > > > > > >
> > > > > > > Signed-off-by: Martin Kletzander <mkletzan@xxxxxxxxxx>
> > > > > > > ---
> > > > > > > meson.build | 3 ---
> > > > > > > src/qemu/qemu_domain.c | 7 +++++++
> > > > > > > src/util/vireventthread.c | 6 ++++++
> > > > > > > src/util/viridentity.c | 6 ++++++
> > > > > > > src/util/virobject.c | 6 ++++++
> > > > > > > 5 files changed, 25 insertions(+), 3 deletions(-)
> > > > > > >
> > > > > > > diff --git a/meson.build b/meson.build
> > > > > > > index cecaad199d4c..04646e3a078c 100644
> > > > > > > --- a/meson.build
> > > > > > > +++ b/meson.build
> > > > > > > @@ -405,9 +405,6 @@ cc_flags += [
> > > > > > > # so use this Clang-specific arg to keep it quiet
> > > > > > > '-Wno-typedef-redefinition',
> > > > > > >
> > > > > > > - # Clang complains about casts in G_DEFINE_TYPE(...)
> > > > > > > - '-Wno-incompatible-pointer-types-discards-qualifiers',
> > > > > > > -
> > > > > > > # We don't use -Wc++-compat so we have to enable it explicitly
> > > > > > > '-Wjump-misses-init',
> > > > > > >
> > > > > > > diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> > > > > > > index 2158080a56ad..3349476cceae 100644
> > > > > > > --- a/src/qemu/qemu_domain.c
> > > > > > > +++ b/src/qemu/qemu_domain.c
> > > > > > > @@ -330,7 +330,14 @@ struct _qemuDomainLogContext {
> > > > > > > virLogManagerPtr manager;
> > > > > > > };
> > > > > > >
> > > > > > > +#pragma clang diagnostic push
> > > > > > > +/* Workaround for glib's issue #600 on clang */
> > > > > > > +#pragma clang diagnostic ignored "-Wincompatible-pointer-types-discards-qualifiers"
> > > > > > > +
> > > > > > > G_DEFINE_TYPE(qemuDomainLogContext, qemu_domain_log_context, G_TYPE_OBJECT);
> > > > > > > +
> > > > > > > +#pragma clang diagnostic pop
> > > > > >
> > > > > > I really don't want to see this pattern used. We may only have a handful
> > > > > > of G_DEFINE_TYPE today, but as we convert all 200 virClass over to GObject
> > > > > > this is going to be way to tedious. This has to be done as a global
> > > > > > thing IMHO.
> > > > > >
> > > > >
> > > > > Even when the warning we're disabling actually catches errors we make every now
> > > > > and then? Really?
> > > >
> > > > You can disable it globall, but only when compiling against the glib versions
> > > > affected. We'll still get coverage of the warning flag when building against
> > > > other versions.
> > > >
> > > > >
> > > > > I know the issue is very old and it only showed up now. And that the MR might
> > > > > not go through for quite some time. But how about a middle ground like the one
> > > > > I described in reply to Pavel? Looks like this:
> > > > >
> > > > > #define G_DEFINE_TYPE_WITH_WORKAROUND(a, b, c) \
> > > > > _Pragma ("clang diagnostic push") \
> > > > > _Pragma ("clang diagnostic ignored \"-Wincompatible-pointer-types-discards-qualifiers\"") \
> > > > > G_DEFINE_TYPE(a, b, c) \
> > > > > _Pragma ("clang diagnostic pop")
> > > > >
> > > > > If someone wants to make sure it does not break and we really want to get rid of
> > > > > this ASAP, then we can even syntax-check for it, describe it and only use it
> > > > > with glib that has this issue.
> > > >
> > > > That can't be done selectively - we would have to use that wrapper macro
> > > > unconditionally, so it'd be present for years until we bump the min glib
> > > > to a version that has the fix.
> > >
> > > So what about something like this:
> > >
> > > #if glib is broken
> > > # undefine G_DEFINE_TYPE
> > > # define G_DEFINE_TYPE \
> > > # some pragma magic (basically what martin has above) \
> > > #endif
> > >
> > > This way we can continue using G_DEFINE_TYPE and ditch this redefine once
> > > glib is updated to fixed version.
> >
> > If you can make that work, that'd be ok as it isolates the workaround in
> > a single place.
> >
>
> OK, thanks Michal for following up because I was kind of misunderstanding the
> intention.
>
> If we #undef the original G_DEFINE_TYPE we would have to open code it, being
> prone to errors if the original definition changes. If we change it to
> e.g. VIR_G_DEFINE_TYPE() (and disable G_DEFINE_TYPE usage out of
> sr/util/glibcompat.c) then we can just do what I wrote above and whenever it is
> removed it is easy to see what places in the code need changing. I know you are
> against that, but I don't see how different that is compared to, for example
> vir_g_canonicalize_filename(). And other functions in gcompat.h also, although
> they don't even have the version check.
No code ever calls vir_g_canonicalize_filename directly, it continues
to use g_canonicalize_filename as normal. The calls get transparently
re-written to vir_g_canonicalize_filename - basically the same hack that
gnulib used to transparently replace functions.
Regards,
Daniel
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