Initial commit

README.md

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+## fluxflop - floppy-sized Linux
+
+
+
+## Pre-reqs
+
+Package:
+```
+apt-get install build-essential gcc-i686-linux-gnu g++-i686-linux-gnu
+```
+Sources:
+```
+wget https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.8.11.tar.xz
+tar -xf linux-6.8.11.tar.xz
+cd linux-6.8.11
+```
+
+Configs:
+```
+cp ./configs/linux/.config linux-6.8.11/.config
+
+```
+
+Root filesystem layout:
+```
+mkdir -p root/{bin,proc,dev,sys,usr}
+
+
+
+# Create a simple init script
+# or compile tools/init.c
+cat > root/init <<EOF
+#!/bin/sh
+# Mount essential filesystems
+mount -t proc none /proc
+mount -t sysfs none /sys
+mount -t devtmpfs none /dev
+
+# Start a shell
+exec /bin/sh -i 
+
+# Infinite loop to prevent the script from exiting
+while true; do
+    sleep 1
+done
+EOF
+
+chmod a+x root/init
+
+mknod -m 660 ./root/dev/console c 5 1
+mknod -m 666 ./root/dev/ttyS0 c 4 64
+mknod -m 666 ./rootdev/tty c 5 0
+
+
+```
+
+Output image directories:
+```
+mkdir -p bootable_image/{boot,isolinux}
+```
+
+
+## Build
+Linux:
+```
+cd linux-6.8.11
+make ARCH=x86 CROSS_COMPILE=i686-linux-gnu- bzImage -j8
+```
+
+
+Toybox:
+```
+wget https://landley.net/toybox/bin/toybox-i486 -O ./root/bin/toybox-i486
+./scripts/toybox-symlinks.sh
+```
+
+Strip debug symbols:
+```
+./scripts/stripfs.sh
+```
+
+
+
+Make the initramfs:
+```
+./scripts/make-cpio.sh
+```
+
+Syslinux for ISOs:
+```
+wget https://mirrors.edge.kernel.org/pub/linux/utils/boot/syslinux/syslinux-6.03.tar.gz
+tar xvf syslinux-6.03.tar.gz
+cd syslinux-6.03
+
+cp syslinux/bios/core/isolinux.bin bootable_image/isolinux
+cp syslinux/bios/com32/elflink/ldlinux/ldlinux.c32 bootable_image/isolinux
+cp configs/isolinux/isolinux.cfg bootable_image/isolinux
+```
+
+## Boot
+Make a bootable ISO:
+```
+./scripts/make-cpio.sh
+```
+and boot with:
+```
+qemu-system-i386 -cdrom out.iso -m 32 -nographic 
+```
+
+
+
+Boot with qemu:
+```
+qemu-system-i386 -kernel ./linux-6.8.11/arch/x86/boot/bzImage -initrd ./rootfs.cpio.gz -append "append init=/init rdinit=/init -m 32 -nographic
+
+```
+
+## Extra
+Use a simple C program to use as init:
+```
+gcc -static -o init tools/init.c
+```
+Use as the initramfs:
+```
+echo init | cpio -ov --format=newc > initramfs.img
+```
+
+__Kernel image comparison with printk support__:
+
+with:
+```
+stat -c %s arch/arm64/boot/Image
+2809864
+```
+
+without:
+```
+stat -c %s arch/arm64/boot/Image
+2283528
+```
+
+__-fomit-frame-pointer__:
+```
+easto@debian-build:~/testing-linux/linux-6.8.11$ ls -ls arch/x86/boot/bzImage 
+728 -rw-r--r-- 1 easto easto 741888 May 30 02:27 arch/x86/boot/bzImage
+
+
+ make KCFLAGS="-fomit-frame-pointer" ARCH=x86 CROSS_COMPILE=i686-linux-gnu- bzImage -j8
+ 
+ easto@debian-build:~/testing-linux/linux-6.8.11$ ls -ls arch/x86/boot/bzImage 
+716 -rw-r--r-- 1 easto easto 729600 May 30 02:30 arch/x86/boot/bzImage
+
+```
+
+## Resources
+
+https://justine.lol/sizetricks/
+
+https://elinux.org/images/7/72/Linux_tiny.pdf
+
+https://git.openembedded.org/meta-micro/tree/conf
+
+https://elinux.org/Linux_Tiny
+
+https://ops.tips/notes/booting-linux-on-qemu/
+
+https://android.googlesource.com/platform/external/syzkaller/+/HEAD/docs/linux/setup_linux-host_qemu-vm_arm64-kernel.md
+
+https://github.com/ahgamut/superconfigure/?tab=readme-ov-file
+
+https://github.com/buildroot/buildroot/tree/master/board/qemu/aarch64-virt

configs/isolinux/isolinux.cfg

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+default 1
+label 1
+    kernel boot/bzImage
+    initrd boot/rootfs.cpio
+    append init=/init rdinit=/init console=ttyS0,115200n8 
+