Understood with your KVM/TCG snapshot comment. I thought it was worth a try.
NOTE: I do not yet understand how gdb interacts with the virtual machine. I have experience with GDB, but only at a linux app-debug level. I don't grok how gdb on a linux host works with QEMU running a windows guest. My *assumption* is that the VM continues to run while an app is being debugged with GDB can be stopped, stepped, etc. If this is the case, I would expect that the VM's sense of time will continue to move forward while the app is paused. This would be an issue for my time-sensitive app. If I slow down the entire QEMU system with my hacks, then my expectation is that the time for both the VM and the app will slow down similarly (if I decouple the VM time from real-world time using the -rtc command-line argument). So... 1) Are my assumptions close? 2) Can someone point me to information on using gdb with QEMU/KVM? Thanks! -S On Thu, Jun 24, 2021 at 11:23 AM Peter Maydell <peter.mayd...@linaro.org> wrote: > On Wed, 23 Jun 2021 at 22:10, Steven Raasch <sraa...@gmail.com> wrote: > > I have used KVM to create a snapshot of a windows-10 guest running a > graphics-intensive app. The *original* issue is that the app does not > execute correctly when re-started from the snapshot using TCG (it doesn't > crash, but it doesn't run correctly, either). > > I'm not sure that taking a snapshot with KVM and then resuming under TCG > is really tested. So I'm not very surprised that it doesn't work. > > > I'm setting DEBUG & single-step modes by calling cpu_single_step() from > the top of kvm_vcpu_thread_fn(). > > in kvm_cpu_exec() I wait until I get a KVM_EXIT_DEBUG signal before > logging the instruction. > > If your app can cope with the slowdown involved in taking a VM exit > after every instruction (which will be massive), then it can probably > also handle the extra overhead on top of that of the gdbstub communication > protocol. So it's probably simplest just to connect to QEMU's gdbstub and > do the single-stepping that way. > > The other approach to this would be to see if intel's perf monitor > stuff (which I know nothing about) has some kind of execution-trace > capture support and if that works when passing through the PMU to a > KVM guest. > > thanks > -- PMM >
