Build QEMU from source

Dockerfile

@@ -1,5 +1,48 @@
-FROM qemu/arm as dockerpi-vm
+ARG QEMU_VERSION=4.2.0
+
+# Build stage for qemu-system-arm
+FROM debian:stable-slim AS qemu-system-arm-builder
+ARG QEMU_VERSION
+ENV QEMU_TARBALL="qemu-${QEMU_VERSION}.tar.xz"
+WORKDIR /qemu
+
+RUN # Update package lists
+RUN apt-get update
+
+RUN # Pull source and verify signatures
+RUN apt-get -y install wget
+RUN wget "https://download.qemu.org/${QEMU_TARBALL}"
+
+RUN # Verify signatures
+RUN apt-get -y install gpg
+RUN wget "https://download.qemu.org/${QEMU_TARBALL}.sig"
+RUN gpg --keyserver keyserver.ubuntu.com --recv-keys CEACC9E15534EBABB82D3FA03353C9CEF108B584
+RUN gpg --verify "${QEMU_TARBALL}.sig" "${QEMU_TARBALL}"
+
+RUN # Extract source tarball
+RUN apt-get -y install pkg-config
+RUN tar xvf "${QEMU_TARBALL}"
+
+RUN # Build source
+# These seem to be the only deps actually required for a successful  build
+RUN apt-get -y install python build-essential libglib2.0-dev libpixman-1-dev
+# These don't seem to be required but are specified here: https://wiki.qemu.org/Hosts/Linux
+RUN apt-get -y install libfdt-dev zlib1g-dev
+# Not required or specified anywhere but supress build warnings
+RUN apt-get -y install pkg-config flex bison
+RUN "qemu-${QEMU_VERSION}/configure" --static --target-list=arm-softmmu
+RUN make -j$(nproc)
+
+RUN # Strip the binary, this gives a substantial size reduction!
+RUN strip "arm-softmmu/qemu-system-arm"
+
+
+# Build the dockerpi VM image
+FROM busybox:1.31 AS dockerpi-vm
 LABEL maintainer="Luke Childs <lukechilds123@gmail.com>"
+ARG QEMU_VERSION
+
+COPY --from=qemu-system-arm-builder /qemu/arm-softmmu/qemu-system-arm /usr/local/bin/qemu-system-arm
 
 ADD https://github.com/dhruvvyas90/qemu-rpi-kernel/archive/afe411f2c9b04730bcc6b2168cdc9adca224227c.zip /tmp/qemu-rpi-kernel.zip
 
@@ -14,6 +57,9 @@ VOLUME /sdcard
 ADD ./entrypoint.sh /entrypoint.sh
 ENTRYPOINT ["./entrypoint.sh"]
 
+
+# Build the dockerpi image
+# It's just the VM image with a compressed Raspbian filesystem added
 FROM dockerpi-vm as dockerpi
 LABEL maintainer="Luke Childs <lukechilds123@gmail.com>"
 ADD http://downloads.raspberrypi.org/raspbian_lite/images/raspbian_lite-2019-09-30/2019-09-26-raspbian-buster-lite.zip /filesystem.zip