xen

That would give the user full control over the physical CPU, though, whereas most "cloud" services only give you access to a virtual machine. On the other hand, it should be possible for the hypervisor to provide roughly the same capabilities in software, without having to modify the software inside the virtual machine. Indeed, most hypervisors already provide a GDB stub for this purpose, including, e.g., Xen [1]; it's just that public clouds don't typically give customers access to it. It would be nice if that changed. [1] https://github.com/xen-project/xen/tree/master/tools/debugge...