kernel: 0.900 device: 0.858 debug: 0.844 files: 0.812 boot: 0.760 semantic: 0.745 ppc: 0.723 user-level: 0.692 arm: 0.689 PID: 0.619 virtual: 0.585 register: 0.551 socket: 0.536 graphic: 0.536 mistranslation: 0.526 architecture: 0.526 performance: 0.525 hypervisor: 0.498 permissions: 0.489 network: 0.410 vnc: 0.388 peripherals: 0.345 risc-v: 0.342 x86: 0.297 VMM: 0.282 TCG: 0.217 assembly: 0.199 i386: 0.191 KVM: 0.165 gdbstub debug of multi-cluster machines is undocumented and confusing Working with Zephyr RTOS, running a multi core sample on mps2_an521 works fine. Both cpus start. Trying to debug with options -s -S the second core fails to boot. Posted with explanation also at: https://github.com/zephyrproject-rtos/zephyr/issues/33635 there was no bug, it was my fault. How do I delete this In general, you don't need to delete bugs that turn out to be user error, or edit the description/title; just mark them as 'invalid', perhaps with a comment about what turned out to be the cause. That leaves the trail of what was going on for future readers who might be going down the same path as you. There are actually a couple of things we should do here in upstream QEMU: * we should document the process for using the debugstub with multi-cluster board models like the mps2-an521 * we should check whether we are doing the right/most appropriate thing when the user connects to the debug stub and is only attaching to one 'inferior' -- it sounds from your report like the un-attached inferior is left permanently in the 'stopped' state. Maybe that's what the gdb protocol requires, but it seems a bit unhelpful. I'm going to update the bug status/text accordingly. Thanks for the answer, indeed the second cluster of the board has been halted when I was starting gdb the "normal" way - not adding the second inferior. In my own research I did not find out about these inferiors, so I was wondering why "info threads" did only show one cpu. Maybe gdb could inform the user about unattached inferiors when using "info threads" Could you provide an example QEMU command line and guest image file which you were having this problem with, please? That would save me figuring out how to build zephyr binaries :-) qemu-system-arm -cpu cortex-m33 -machine mps2-an521 -nographic -m 16 -vga none -net none -chardev stdio,id=con,mux=on -serial chardev:con -mon chardev=con,mode=readline -icount shift=7,align=off,sleep=off -rtc clock=vm -device loader,file=/zephyr.elf -s -S -kernel /zephyr.elf i've included both .elf files in a zip. That should be enough for running the sample There's now a new docs section on debugging multicore (including multi-cluster) machines: https://qemu-project.gitlab.io/qemu/system/gdb.html#debugging-multicore-machines Is there still anything to do here or could we close the ticket now? It can be closed. The added documentation is very helpful. Ok, thanks, so I'm closing this ticket now.