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.
- Changed grub.cfg from 'multiboot' to 'multiboot2' command. The PMM parses
Multiboot2 tag structures, but GRUB was booting with Multiboot1 protocol,
causing the memory map parsing to silently fail (all memory stayed marked
as used, leading to OOM on every allocation).
- Fixed BITMAP_SIZE calculation to properly round up instead of truncating,
ensuring the last few pages of the address space are covered.
- Fixed sign comparison warning in bitmap init loop.
- Added debug output to PMM init (mem_upper, region count) for diagnostics.
- Removed stale Multiboot1 magic constant and (void)addr cast from kernel.c.
- Added documentation for the interrupt subsystem and PMM in docs/.
- Checked off 'Implement a PIC handler' and 'Create a physical memory
allocator' in the task list.
Tested: kernel boots in QEMU with both 4MB and 128MB RAM, PMM correctly
allocates from NORMAL zone (0x01000000) and DMA zone (0x00001000).
This commit adds GDT initialization with proper code/data segments and reloads CS.
It also adds the initial IDT structure and loads an empty IDT.
Build configuration updated to disable SSE/MMX to prevent compiler generation of unsupported instructions in early boot.
