On Thu, 5 Sep 2019 at 09:52, Marc Zyngier <maz@xxxxxxxxxx> wrote: > > On Thu, 05 Sep 2019 09:16:54 +0100, > Peter Maydell <peter.maydell@xxxxxxxxxx> wrote: > > This is true, but the problem is that barfing out to userspace > > makes it harder to debug the guest because it means that > > the VM is immediately destroyed, whereas AIUI if we > > inject some kind of exception then (assuming you're set up > > to do kernel-debug via gdbstub) you can actually examine > > the offending guest code with a debugger because at least > > your VM is still around to inspect... > > To Christoffer's point, I find the benefit a bit dubious. Yes, you get > an exception, but the instruction that caused it may be completely > legal (store with post-increment, for example), leading to an even > more puzzled developer (that exception should never have been > delivered the first place). Right, but the combination of "host kernel prints a message about an unsupported load/store insn" and "within-guest debug dump/stack trace/etc" is much more useful than just having "host kernel prints message" and "QEMU exits"; and it requires about 3 lines of code change... > I'm far more in favour of dumping the state of the access in the run > structure (much like we do for a MMIO access) and let userspace do > something about it (such as dumping information on the console or > breaking). It could even inject an exception *if* the user has asked > for it. ...whereas this requires agreement on a kernel-userspace API, larger changes in the kernel, somebody to implement the userspace side of things, and the user to update both the kernel and QEMU. It's hard for me to see that the benefit here over the 3-line approach really outweighs the extra effort needed. In practice saying "we should do this" is saying "we're going to do nothing", based on the historical record. thanks -- PMM _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
