- Created apps/hello-world/hello-world.S: AT&T assembly user program that
calls SYS_WRITE to print 'Hello, World' then SYS_EXIT(0)
- Created apps/user.ld: linker script for user apps at 0x08048000
- Created scripts/build_apps.sh: builds each app dir into flat binary
- Updated CMakeLists.txt: added apps build target in ISO pipeline
- Updated gen_initrd.sh: packs built binaries from build/apps_bin/
- Updated kernel.c: replaced inline machine code with VFS-based loading
of hello-world from /initrd/hello-world via cpio_find()
Verified: hello-world binary (49 bytes) loads from CPIO initrd,
prints 'Hello, World', and exits with code 0.
Build system changes:
- scripts/gen_initrd.sh packs all files from apps/ into a newc-format
CPIO archive at build/isodir/boot/initrd.cpio.
- CMakeLists.txt adds 'initrd' target as ISO dependency. GRUB loads the
archive as a Multiboot2 module via 'module2 /boot/initrd.cpio'.
- apps/README added as placeholder file for initial ramdisk content.
Kernel changes:
- kernel.c scans Multiboot2 tags for MULTIBOOT_TAG_TYPE_MODULE to find
the initrd's physical address range, then passes it to cpio_init().
- cpio.c/h implements a parser for the SVR4/newc CPIO format:
- cpio_init(): lists archive contents on startup
- cpio_find(): look up a file by name (handles ./ prefix)
- cpio_next(): iterate through all entries
- cpio_count(): count files in archive
- The initrd lives in identity-mapped physical memory, so no additional
mapping is needed to access it.
Verified in QEMU: GRUB loads the module at 0x0014A000, CPIO parser
finds the README file (38 bytes). All existing functionality (Ring 3
processes, syscalls) continues to work.
