QEMU and Linux Kernel

The original and complete text can be found here.

QEMU can be used for debugging Linux kernel. The text below, is small piece of the entire text which can be found here. Basically, after compiling the Linux kernel, it’s possible to load the compiled kernel on QEMU for debugging.

After compiling the kernel…

The results of this are basically two files: You will have a vmlinux that contains both the code and the corresponding debug information in the directory of the kernel source code. The architecture subdirectory – this is arch/x86/boot/ for the x86 platform – contains the compressed kernel in bzImage. Other platforms might call the kernel zImage. Bootloaders such as GRUB need the compressed kernel (bzImage). The debugger itself also needs the kernel image but will use the uncompressed counterpart vmlinux, which contains the debug info. Of course, the debugger also needs access to the source code.

Once you have generated the kernel and the root filesystem with Build-root, you should first test both without debugging:

qemu -kernel output/images/bzImage -hda output/images/rootfs.ext2 -append "root=/dev/sda rw"

If everything works, you can start debugging by appending -s and -S:

qemu -kernel output/images/bzImage -hda output/images/rootfs.ext2 -append "root=/dev/sda rw" -s -S

The -s option launches the debug server (gdbserver), and -S stops the kernel at the outset.

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