Download the TinyCore Linux ISO:

curl -O https://mirrors.dotsrc.org/tinycorelinux/8.x/x86/release/TinyCore-8.2.1.iso</code.
  * Create mount points<code>sudo mkdir -p /mnt/{image,iso}

Create disk image

qemu-img create -f raw tc.raw 64M

Mount image as blockdevice

sudo losetup /dev/loop0 tc.raw
sudo kpartx -a /dev/loop0

Create partition table on disk image

sudo parted --script /dev/loop0 \
    mklabel msdos \
    mkpart primary 1MiB 100% \
    toggle 1 boot

Create filesystem

sudo mkfs.ext2 /dev/mapper/loop0p1

Mount image and ISO

sudo mount /dev/mapper/loop0p1 /mnt/image
sudo mount -o loop TinyCore-8.2.1.iso /mnt/iso

Create directories

sudo mkdir -p /mnt/image/{boot,tce,tce/optional}

Copy TinyCore to disk image

sudo cp /mnt/iso/boot/core.gz /mnt/image/boot/
sudo cp /mnt/iso/boot/vmlinuz /mnt/image/boot/
sudo cp /mnt/iso/cde/onboot.lst /mnt/image/tce/
sudo cp /mnt/iso/cde/optional/* /mnt/image/tce/optional/

Install GRUB (grub2-… on Fedora/RedHat)

sudo grub2-install --target=i386-pc --boot-directory=/mnt/image/boot /dev/loop0

Configure grub

sudo bash -c "cat > /mnt/image/boot/grub2/grub.cfg" <<'EOF'
set timeout=5
set root='hd0,msdos1'
menuentry 'TinyCore 8.2.1' {
    linux /boot/vmlinuz quiet noswap
    initrd /boot/core.gz
}
EOF

Test boot image

cd; sudo umount /mnt/{iso,image}

qemu-system-x86_64 \
    -vga qxl \
    -soundhw ac97 \
    -enable-kvm \
    -m 2G \
    -hda tc.raw \
    -boot c \
    -usb \
    -device usb-ehci,id=ehci \
    -device usb-tablet,bus=usb-bus.0