On Tuesday, May 03, 2011 1:43:39 pm Kostik Belousov wrote:
> On Tue, May 03, 2011 at 11:44:32AM -0400, John Baldwin wrote:
> > On Tuesday, May 03, 2011 9:10:26 am Philip Soeberg wrote:
> > > Hi fellow FreeBSD hackers,
> > >
> > > I've been using the following poor-man's approach in my driver init for
> > > ages in an attempt at detecting PAE option on BSD 6 (or greater) i386
> > > kernels, as I depend on dmabus(9) but provide a loadable kernel module
> > > only.
> > >
> > > >>>
> > > if (sizeof(void*) == 4) {
> > > if (((uint64_t)(cnt.v_page_count * cnt.v_page_size) / 1073741824)
> > > >= 4) {
> > > printf("FreeBSD i386 detected with PAE option enabled. FreeBSD
> > > PAE type\n");
> > > printf("kernels does not support loadable modules which use DMA.
> > > Please\n");
> > > printf("reconfigure your kernel for non-PAE or switch to amd64
> > > kernel.\n");
> > > return EFAULT;
> > > }
> > > }
> > > <<<
> >
> > Hmmm, even this isn't really accurate as some folks may choose to enable PAE
> > even with < 4GB to get PG_NX functionality.
> >
> > > afaik there's a sysctl method of checking this per BSD7 (or is it 8?),
> > > but what about BSD6? Any hints on how I can runtime detect the above?
> >
> > Definitely a kern.features.pae sysctl in 7. I don't see anything similar
> > in
> > 6.
>
> Read %cr4 and test the bit there.
Oh, cute. :)
--
John Baldwin
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