A simple x86 firmware that can boot Linux.

Most of QEMU's startup time is spent:

in the dynamic linker. This can be reduced by 150 ms simply by compiling a stripped down QEMU:

./configure --disable-libssh2 --disable-tcmalloc --disable-glusterfs
--disable-seccomp --disable-{bzip2,snappy,lzo} --disable-usb-redir
--disable-libusb --disable-smartcard-nss --disable-libnfs
--disable-libiscsi --disable-rbd --disable-spice --disable-attr
--disable-cap-ng --disable-linux-aio --disable-brlapi
--disable-vnc-{jpeg,tls,sasl,png,ws} --disable-rdma --disable-bluez
--disable-fdt --disable-curl --disable-curses --disable-sdl
--disable-gtk --disable-tpm --disable-vte --disable-vnc
--disable-xen --disable-opengl --target-list=x86_64-softmmu
in the BIOS. qboot saves another 150 ms.
until QEMU 2.7+, in fw_cfg. qboot uses the DMA interface which is pretty much instantaneous.

Compile qboot

Clone the source:

$ git clone https://github.com/bonzini/qboot.git

Compile the qboot firmware (you may need to install the relevant build time dependancies):

$ meson build && ninja -C build

The result will be a 64K file named bios.bin under the build/ directory.

Usage

$ qemu-kvm -bios bios.bin \
  -kernel /boot/vmlinuz-4.0.3-300.fc22.x86_64 \
  -serial mon:stdio -append 'console=ttyS0,115200,8n1'