add proper x86 build (not proper enough to work but 'more correct')

README.md

@@ -1,3 +1,11 @@
 # minimal-linux
 
-A minimal linux distro with busybox. Don't know if this works properly
+A minimal linux distro with busybox. Kernel loads up in Qemu but doesn't "init" into shell properly yet.
+
+## build from scratch
+
+Just do: `./build.sh`
+
+### test with QEMU
+
+`./start-vm.sh`

build.sh

@@ -0,0 +1,119 @@
+set -e
+set -u
+
+OUTDIR=/minimal-linux
+KERNEL_REPO=git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
+KERNEL_VERSION=v6.1.14
+BUSYBOX_VERSION=1_33_1
+
+#ARCH=arm64
+#CROSS_COMPILE=aarch64-none-linux-gnu-
+ARCH=x86_64
+CROSS_COMPILE=
+
+if [ $# -lt 1 ]
+then
+	echo "Using default directory ${OUTDIR} for output"
+else
+	OUTDIR=$1
+	echo "Using passed directory ${OUTDIR} for output"
+fi
+
+mkdir -p ${OUTDIR}
+
+cd "$OUTDIR"
+if [ ! -d "${OUTDIR}/linux-stable" ]; then
+    #Clone only if the repository does not exist.
+	echo "CLONING GIT LINUX STABLE VERSION ${KERNEL_VERSION} IN ${OUTDIR}"
+	git clone ${KERNEL_REPO} --depth 1 --single-branch --branch ${KERNEL_VERSION}
+fi
+if [ ! -e ${OUTDIR}/linux-stable/arch/${ARCH}/boot/Image ]; then
+    cd linux-stable
+    echo "Checking out version ${KERNEL_VERSION}"
+    git checkout ${KERNEL_VERSION}
+    # https://unix.stackexchange.com/questions/657882/how-do-i-cross-compile-the-linux-kernel
+    #make ARCH="$ARCH" CROSS_COMPILE="$CROSS_COMPILE" menuconfig
+    #make ARCH="$ARCH" CROSS_COMPILE="$CROSS_COMPILE" config
+    # use default config
+    make ARCH="$ARCH" CROSS_COMPILE="$CROSS_COMPILE" defconfig
+    make ARCH="$ARCH" CROSS_COMPILE="$CROSS_COMPILE"
+fi
+
+echo "Adding the Image in outdir"
+
+cp ${OUTDIR}/linux-stable/arch/x86/boot/bzImage ${OUTDIR}
+
+echo "Creating the staging directory for the root filesystem"
+cd "$OUTDIR"
+if [ -d "${OUTDIR}/rootfs" ]
+then
+	echo "Deleting rootfs directory at ${OUTDIR}/rootfs and starting over"
+    sudo rm  -rf ${OUTDIR}/rootfs
+fi
+
+# TODO: Create necessary base directories
+mkdir rootfs/
+mkdir rootfs/bin
+mkdir rootfs/dev
+mkdir rootfs/etc
+mkdir rootfs/home
+mkdir rootfs/lib
+mkdir rootfs/lib/modules
+mkdir rootfs/lib64
+mkdir rootfs/lib64/modules
+mkdir rootfs/proc
+mkdir rootfs/sys
+mkdir rootfs/sbin
+mkdir rootfs/tmp
+mkdir rootfs/usr
+mkdir rootfs/usr/lib
+mkdir rootfs/usr/bin 
+mkdir rootfs/usr/sbin
+mkdir rootfs/var
+mkdir rootfs/var/log 
+
+cd "$OUTDIR"
+if [ ! -d "${OUTDIR}/busybox" ]
+then
+git clone git://busybox.net/busybox.git
+    cd busybox
+    git checkout ${BUSYBOX_VERSION}
+    # TODO:  Configure busybox
+    # https://busybox.net/FAQ.html#configure
+    make ARCH="$ARCH" CROSS_COMPILE="$CROSS_COMPILE" defconfig
+else
+    cd busybox
+fi
+
+# TODO: Make and install busybox
+make ARCH="$ARCH" CROSS_COMPILE="$CROSS_COMPILE"
+make ARCH="$ARCH" CROSS_COMPILE="$CROSS_COMPILE" CONFIG_PREFIX="${OUTDIR}/rootfs" install
+cd ..
+pwd
+
+echo "Library dependencies"
+${CROSS_COMPILE}readelf -a ${OUTDIR}/rootfs/bin/busybox | grep "program interpreter"
+${CROSS_COMPILE}readelf -a ${OUTDIR}/rootfs/bin/busybox | grep "Shared library"
+
+# TODO: Add library dependencies to rootfs
+SYSROOT=$(${CROSS_COMPILE}gcc -print-sysroot)
+echo "SYSROOT is : $SYSROOT"
+cp -a ${SYSROOT}/lib64/ld-linux-x86-64.so.2 ${OUTDIR}/rootfs/lib
+echo "cp 1 result $#"
+cp -r ${SYSROOT}/lib64/ ${OUTDIR}/rootfs/lib64
+echo "cp 2 result $#"
+
+# TODO: Make device nodes
+cd ${OUTDIR}/rootfs
+sudo mknod -m 666 dev/null c 1 3
+sudo mknod -m 600 dev/console c 5 1
+ls -l dev
+
+# TODO: Chown the root directory
+cd "$OUTDIR/rootfs"
+sudo chown -R root:root *
+
+# TODO: Create initramfs.cpio.gz
+find . | cpio -H newc -ov --owner root:root > ${OUTDIR}/initramfs.cpio
+cd "$OUTDIR"
+gzip -f initramfs.cpio

start-vm.sh

@@ -0,0 +1,37 @@
+# !/bin/bash
+# Script to test build using qemu x86 emulator.
+
+set -e
+
+OUTDIR=$1
+
+if [ -z "${OUTDIR}" ]; then
+    OUTDIR=/minimal-linux
+    echo "No outdir specified, using ${OUTDIR}"
+fi
+
+KERNEL_IMAGE=${OUTDIR}/linux-stable/arch/x86/boot/bzImage
+INITRD_IMAGE=${OUTDIR}/initramfs.cpio.gz
+
+if [ ! -e ${KERNEL_IMAGE} ]; then
+    echo "Missing kernel image at ${KERNEL_IMAGE}"
+    exit 1
+fi
+if [ ! -e ${INITRD_IMAGE} ]; then
+    echo "Missing initrd image at ${INITRD_IMAGE}"
+    exit 1
+fi
+
+
+echo "Booting the kernel"
+# See trick at https://superuser.com/a/1412150 to route serial port output to file
+qemu-system-x86_64 \
+        -m 256M \
+        -M pc \
+        -cpu qemu64 \
+        -nographic \
+        -smp 1 \
+        -kernel ${KERNEL_IMAGE} \
+        -chardev stdio,id=char0,mux=on,logfile=${OUTDIR}/serial.log,signal=off \
+        -serial chardev:char0 -mon chardev=char0 \
+        -append "rdinit=/home/autorun-qemu.sh console=ttyAMA0" -initrd ${INITRD_IMAGE}