Re: [Xen-devel] [PATCH v3 5/5] xen: modify several static locks to unique names

[Juergen Gross <jgross@xxxxxxxx>]

On 04.09.19 10:51, Jan Beulich wrote:
> On 04.09.2019 10:47, Juergen Gross wrote:
> > On 04.09.19 10:40, Jan Beulich wrote:
> > > On 04.09.2019 10:25, Juergen Gross wrote:
> > > > On 03.09.19 17:09, Jan Beulich wrote:
> > > > > On 03.09.2019 17:03, Juergen Gross wrote:
> > > > > > On 03.09.19 16:53, Jan Beulich wrote:
> > > > > > > On 29.08.2019 12:18, Juergen Gross wrote:
> > > > > > > > In order to have unique names when doing lock profiling several local
> > > > > > > > locks "lock" need to be renamed.
> > > > > > > But these are all named simply "lock" for a good reason, including
> > > > > > > because they're all function scope symbols (and typically the
> > > > > > > functions are all sufficiently short). The issue stems from the
> > > > > > > dual use of "name" in
> > > > > > >
> > > > > > > #define _LOCK_PROFILE(name) { 0, #name, &name, 0, 0, 0, 0, 0 }
> > > > > > >
> > > > > > > so I'd rather suggest making this a derivation of a new
> > > > > > >
> > > > > > > #define _LOCK_PROFILE_NAME(lock, name) { 0, #name, &lock, 0, 0, 0, 0, 0 }
> > > > > > >
> > > > > > > if there's no other (transparent) way of disambiguating the names.
> > > > > > This will require to use a different DEFINE_SPINLOCK() variant, so e.g.
> > > > > > DEFINE_SPINLOCK_LOCAL(), which will then include the needed "static" and
> > > > > > add "@<func>" to the lock profiling name. Is this okay?
> > > > > To be frank - not really. I dislike both, and would hence prefer to
> > > > > stick to what there is currently, until someone invents a transparent
> > > > > way to disambiguate these. I'm sorry for being unhelpful here.
> > > > I think I have found a way: I could add __FILE__ and __LINE__ data to
> > > > struct lock_profile. In lock_prof_init() I could look for non-unique
> > > > lock names and mark those to be printed with the __FILE__ and __LINE__
> > > > data added to the names.
> > > >
> > > > Would you be fine with this approach?
> > > I would be, but I'm afraid Andrew won't (as with any new uses of __LINE__).
> > > I wonder if __func__ or __FUNCTION__ could be used - the main question is
> > > how they behave when used outside of a function. If either would be NULL
> > > (rather than triggering a diagnostic), it might be usable here. Of course
> > > this would be fragile if just based on observed (rather than documented)
> > > behavior.
> > With gcc 7.4.1 it fails:
> >
> > /home/gross/xen/xen/include/xen/spinlock.h:80:41: error: ‘__func__’ is
> > not defined outside of function scope [-Werror]
> >    #define _LOCK_PROFILE(name) { 0, #name, __func__, &name, 0, 0, 0, 0, 0 }
> Right, as I was afraid of. But __PRETTY_FUNCTION__ looks to be suitable
> (as per the gcc doc, and as per there being clear indications that clang
> also supports this).
Yes, this is working. Will modify the patch.


Juergen

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