On Sat, Jul 09, 2011 at 12:29:01AM +0100, Peter Maydell wrote: > On 8 July 2011 19:32, Nicolas Pitre <nicolas.pi...@linaro.org> wrote: > > On Fri, 8 Jul 2011, Dave Martin wrote: > >> On Fri, Jul 08, 2011 at 12:21:27AM +0100, David Gilbert wrote: > >> > Nicolas just added; Richard's argument is that if it was actually a > >> > VDSO I'd just have linked against a symbol and if the symbol wasn't > >> > there then I would have got a fairly normal linker error - I wouldn't > >> > have needed any special code; and to be honest I think that would also > >> > solve the problem that accessing that wacky address is also a pain for > >> > things like qemu because we're going to have to intercept that read. > >> > >> Note that pre-existing code already calls into the vectors page. > > > > Right, qemu must be intercepting it already. The kernel helpers located > > at a fixed address in the vector page have been around for more than 6 > > years. > > QEMU supports calls into the fixed vector page (it just special cases > attempts to execute at addresses >= 0xffff0000 and emits code to do > "cause special purpose exception" so we get control back at runtime). > What it doesn't support is attempts to do a load from the vector page, > because so far nobody has had a need to probe the vector page for what > it supports.
To solve that particular problem, can you just map a page in RAM with the right content for __kernel_helper_version? The value there can be a static feature of QEMU, indicating which kuser helper functions QEMU knows how to emulate. User processes shouldn't read anything else from the vectors page, at least for now. Cheers ---Dave _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
