On 17 March 2014 05:13, Peter Crosthwaite <peter.crosthwa...@xilinx.com> wrote: > On Fri, Mar 7, 2014 at 5:32 AM, Peter Maydell <peter.mayd...@linaro.org> > wrote: >> Suppress the ID_AA64DFR0_EL1 PMUVer field, even if the CPU specific >> value claims that it exists. QEMU doesn't currently implement it, >> and not advertising it prevents the guest from trying to use it >> and getting UNDEFs on unimplemented registers. >> >> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> > > Reviewed-by: Peter Crosthwaite <peter.crosthwa...@xilinx.com> > >> --- >> This is arguably a hack, but otherwise Linux tries to prod >> half a dozen PMU sysregs. > > Not really. I think sane self-identification trumps dummy feature > advertising. Although there is a consistency argument to be made, as > to whether you should also wipe-out any other features advertised by > this register and friends (e.g. should TraceVer be set?).
The lack of consistency is what makes it a hack :-) Generally QEMU takes the approach of "report what the h/w reports even if we don't implement it all"; "report what we provide even if that's not the same values as h/w" would be a different approach, but if we wanted that we'd need to do it consistently. Still I think pragmatism wins out here. thanks -- PMM
