cvs commit: src/sys/i386/include atomic.h
jhb at freebsd.org
Tue Mar 28 20:01:05 UTC 2006
On Tuesday 28 March 2006 14:28, Dag-Erling Smørgrav wrote:
> John Baldwin <jhb at freebsd.org> writes:
> > On Tuesday 28 March 2006 13:05, Dag-Erling Smørgrav wrote:
> > > John Baldwin <jhb at freebsd.org> writes:
> > > > One reason for not having the casts, btw, is that you lose type
> > > > checking.
> > > Huh? Before my patch, any use of atomic_*_ptr with warnings turned
> > > off would result in a slew of warnings because you'd be passing
> > > pointers to a function which is declared to take u_int. The only way
> > > to make this type safe is to use inline functions instead of the
> > > macros I wrote.
> > s/off/on/ I trust
> > Not true. The tinderbox would attest to that. Please see code such as
> > this: [...]
> which uses uintptr_t, not actual pointers, to avoid warnings. In
> effect, that code is broken.
No, it's on _purpose_, because we do arithmetic on the value (setting
flags, etc.) We happen to use curthread as our cookie value, but
the cookie is an integer, not a pointer.
> Apply the attached patch, see how far a buildkernel gets...
Your patch could break the kernel, as it doesn't say that the value
being modified is volatile (volatile void ** != volatile uintptr_t *).
I can't even get cdecl to tell me how to declare a pointer to a volatile
> I think the proper thing to do, to cover all your bases, would be to
> define a MD atomic_*_intptr family which operated on uintptr_t, and
> define an MI atomic_*_ptr family which operates on void * based on
*sigh* Where were you 6 months ago when I changed atomic_foo_ptr() to
use uintptr_t rather than void *? (For very valid reasons you haven't
bothered to research?)
> > Even userland uses casts when it uses void * rather than uintptr_t for
> > the underlying type. See src/lib/libpthread/sys/lock.c or
> > src/lib/libthr/thr_umtx.h.
> The latter only works because libthr is built with warnings disabled.
> I just finished working on making it build at WARNS level 2; higher
> levels will require a major overhaul, because the kernel interface it
> uses is fundamentally broken.
No, it needs to use the correct casts. We've been through this, the
atomic(9) manpage covers it, etc.
John Baldwin <jhb at FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" = http://www.FreeBSD.org
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