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QEMU for Kernel Development
Purpose
Guide agents through QEMU-based kernel and driver development workflows: building/booting custom kernels, attaching virtio block/network, using Buildroot or minimal initramfs, and rapid module test cycles — focused on kernel dev vs general skills/virtualization/qemu-kvm.
When to Use
- Test kernel patch without bare metal
- Develop driver against virtio or emulated DT platform
- CI kernel boot smoke test
- NFS or 9p root for fast edit-compile-test
Workflow
1. Minimal direct kernel boot (arm64 virt)
bash
qemu-system-aarch64 \
-machine virt -cpu cortex-a57 -smp 4 -m 2G \
-kernel arch/arm64/boot/Image \
-append "console=ttyAMA0 root=/dev/vda rw" \
-drive if=virtio,file=rootfs.ext4,format=raw \
-netdev user,id=net0 -device virtio-net-device,netdev=net0 \
-nographicx86_64:
bash
qemu-system-x86_64 -enable-kvm -m 4G -smp 4 \
-kernel arch/x86/boot/bzImage \
-append "console=ttyS0 root=/dev/vda rw" \
-drive file=rootfs.img,format=raw,if=virtio \
-nographic2. Buildroot rootfs loop
bash
cd buildroot
make qemu_aarch64_virt_defconfig
make
# output/images/Image, rootfs.ext4Integrate custom kernel: set BR2_LINUX_KERNEL_CUSTOM_VERSION or external tree.
3. Out-of-tree module test
bash
# on host — cross build
make -C $KERNEL_SRC M=$PWD modules
# in guest or via initramfs
insmod mydriver.ko
dmesg | tailShare tree with 9p:
bash
-fsdev local,id=dev,path=$PWD,security_model=none \
-device virtio-9p-pci,fsdev=dev,mount_tag=hostshare
# guest: mount -t 9p -o trans=virtio hostshare /mnt4. GDB stub for kernel
bash
qemu-system-aarch64 ... -s -S
gdb vmlinux
(gdb) target remote :1234
(gdb) break start_kernelUse CONFIG_KGDB for live kernel debugging after boot.
5. Device tree overrides
bash
qemu-system-aarch64 -machine virt -dtb myboard.dtb ...virt machine provides virtio devices; platform drivers can target QEMU -device models.
6. Agent usage
/qemu-for-kernel-development Boot arm64 virt with custom Image and virtio rootfs for driver CICommon Problems
| Symptom | Cause | Fix |
|---|---|---|
| Kernel panic no root | Wrong root= | root=/dev/vda for virtio blk |
| No console output | Missing console= on cmdline | console=ttyAMA0 / ttyS0 |
| Module vermagic error | Built against wrong tree | Same KERNEL_SRC as booted image |
| Slow without KVM | TCG emulation | -enable-kvm on x86 host |
| DTB mismatch | Wrong machine | Use virt DTB from kernel make dtbs |
Related Skills
skills/virtualization/qemu-kvm— KVM, VFIO, libvirtskills/qemu/qemu-embedded-simulation— bare-metal MCU QEMUskills/kernel/kernel-testing— KUnit, kselftestskills/kernel-dev/device-tree— DT for virt/platformskills/debuggers/gdb— remote GDB basics
