Date: Tue, 28 Mar 2006 15:01:05 -0500 From: John Baldwin <jhb@freebsd.org> To: "Dag-Erling =?iso-8859-1?q?Sm=F8rgrav?=" <des@des.no> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/i386/include atomic.h Message-ID: <200603281501.08699.jhb@freebsd.org> In-Reply-To: <86acbawerh.fsf@xps.des.no> References: <200603281434.k2SEYmaR031447@repoman.freebsd.org> <200603281358.26703.jhb@freebsd.org> <86acbawerh.fsf@xps.des.no>
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On Tuesday 28 March 2006 14:28, Dag-Erling Sm=F8rgrav wrote: > John Baldwin <jhb@freebsd.org> writes: > > On Tuesday 28 March 2006 13:05, Dag-Erling Sm=F8rgrav wrote: > > > John Baldwin <jhb@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: [...] >=20 > 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 ** !=3D volatile uintptr_t *). I can't even get cdecl to tell me how to declare a pointer to a volatile void pointer. > 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 > that. *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. >=20 > 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. =2D-=20 John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" =3D http://www.FreeBSD.org
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