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<think>
Okay, so I'm trying to help someone who's having trouble running QEMU on their Jetson Nano. They're encountering an "Illegal instruction" crash when they try to boot Raspbian Buster using the native emulation setup from a GitHub repo.
First, let me understand what they've done. They built QEMU from source with KVM enabled and are trying to emulate a Raspberry Pi 3. But instead of getting into the OS, they hit an Illegal instruction error. When they tried to use GDB, it pointed them to code_gen_buffer in TCG (Translation Control Unit) part of QEMU.
They also noticed that when they enable KVM with the -enable-kvm option, they get a different error about image format and an assertion failure because KVM is enabled while trying to do something related to physical memory. That seems like it's conflicting with how QEMU is handling the machine setup.
So why would TCG be used even though KVM is present? Maybe their system doesn't support KVM for aarch64, or perhaps there are some compatibility issues. I remember that on ARM systems, especially when using devices like the Jetson Nano, which has an arm64 architecture, sometimes the kernel might not have the necessary virtualization extensions enabled.
Looking at their QEMU configuration, they included --enable-kvm in their build, so the option is there. But maybe KVM isn't properly supported or initialized for aarch64 emulation on their setup. Alternatively, perhaps the way they're invoking QEMU is incorrect—maybe they need to specify more parameters or use different machine types when enabling KVM.
The Illegal instruction error suggests that the CPU is executing an instruction it doesn't recognize. Since they're running an arm64 build of QEMU (qemu-system-aarch64), and trying to emulate a Raspberry Pi 3 which is a 32-bit ARM device, there might be some mismatch in how the instructions are being translated or executed.
Also, when KVM is enabled, it's supposed to use hardware virtualization. But if their Jetson Nano doesn't have proper support for that (like missing kernel modules or not having the necessary virtualization features enabled), QEMU would fall back to TCG which might cause performance issues and possible crashes.
The error message when enabling KVM mentions an assertion failure in physmem.c. That probably means that QEMU tried to do something it shouldn't have with KVM enabled, possibly because it's trying to use a feature that isn't compatible with KVM.
So, putting this together: the Illegal instruction crash is likely due to TCG trying to run instructions that aren't supported by their CPU or some misconfiguration in how QEMU is handling the guest OS. The assertion when using KVM suggests that either KVM isn't properly set up on their system or the specific setup they're using (raspi3, aarch64) doesn't play well with KVM.
Since the issue involves trying to run an emulation of another system (Raspbian Buster), and it's dealing with hardware virtualization and memory management, this seems more like a system-mode issue. It's related to how QEMU interacts with the host kernel, device drivers, and virtualized peripherals.
</think>
system
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