Re: [PATCH] disable lock annotation with clang 3.4.2

[Thomas Monjalon <thomas@monjalon.net>]

13/02/2023 17:36, Raslan Darawsheh:
> From: Morten Brørup <mb@smartsharesystems.com>
> > From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> > > On Mon, Feb 13, 2023 at 03:44:55PM +0100, David Marchand wrote:
> > > > Venerable RHEL7 clang 3.4.2 has (at least) two issues with lock
> > > > annotations.
> > > >
> > > > A first one with regards to the attribute position:
> > > > ../lib/vhost/vhost.h:518:2: error: GCC does not allow
> > > > 	assert_exclusive_lock attribute in this position on a
> > > > 	function definition [-Werror,-Wgcc-compat]
> > > >         __rte_assert_exclusive_lock(&vq->access_lock)
> > > >         ^
> > > > ../lib/eal/include/rte_lock_annotations.h:29:38: note: expanded
> > > > 	from macro '__rte_assert_exclusive_lock'
> > > >         __attribute__((assert_exclusive_lock(__VA_ARGS__)))
> > > >                                             ^
> > > >
> > > > This can be worked around by splitting and having the allocation on
> > > the
> > > > function declaration.
> > > >
> > > > But on the other hand, clang 3.4.2 does not seem to propagate those
> > > > annotations in presence of a __builtin_expect (i.e. unlikely()), like
> > > > for example when calling if (unlikely(rte_spinlock_trylock() == 0)).
> > > >
> > > > Those annotations were only working with clang in any case, so
> > > restrict
> > > > to clang versions newer than 3.5.0.
> > > >
> > > > Fixes: 657a98f38940 ("eal: annotate spinlock, rwlock and seqlock")
> > > >
> > > > Signed-off-by: David Marchand <david.marchand@redhat.com>
[...]
> > > Are we likely to see any issues with this with any other compilers?
> > > Should
> > > we look to do a built-test in meson to determine feature support rather
> > > than checking clang versions explicitly?
> > >
> > > On the plus side, checking clang version like this makes it clear when
> > > we
> > > can drop the conditional.
> > 
> > I prefer this over auto-detection in meson, for the reason mentioned by
> > Bruce.
> > 
> > Furthermore, different compilers may use different syntax in the code, so it
> > is impossible to detect generically; the auto-detection would be per compiler
> > anyway.
> > 
> > Acked-by: Morten Brørup <mb@smartsharesystems.com>
> Tested-by: Raslan Darawsheh <rasland@nvidia.com>

Applied, thanks.