nexoniarz/SchOS
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Initial commit: Schunix as it stands before the SchOS rename

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An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.
This commit is contained in:
Nexoniarz 2026-08-09 13:47:01 +02:00
commit d0f7acf9eb
275 changed files with 51417 additions and 0 deletions
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48
boot/cdboot.S Normal file
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# Stage 1 for optical media -- the El Torito "no emulation" boot sector.
#
# This exists because bootasm.S cannot boot a CD. It loads stage 2 by talking
# straight to the primary IDE controller's ATA registers, and a CD is not an
# ATA disk: it answers to the ATAPI packet interface instead, and under
# El Torito it may not even be the drive at 0x1F0. Rather than teach a
# 512-byte sector two protocols, optical media get their own first stage.
#
# It has almost nothing to do, because El Torito's "load segment / sector
# count" fields do the reading for us: tools/mkiso.sh asks for
# 1 + STAGE2_SECTORS virtual sectors at 0x7C00, so by the time this runs the
# BIOS has already placed stage 2 at 0x7E00 -- exactly where bootasm.S would
# have put it. The only real work is recording *which* medium we came from,
# since stage2main.c has to read the kernel back with the matching protocol.
#
# The flag goes next to the verbose-boot flag, one byte past it, for the same
# reason that one sits where it does: it is clear of the 256-byte VBE mode
# info block at 0x30000 that stage2.S fills in a moment from now.
#define STAGE2_ADDR 0x7E00
#define BOOT_MEDIA_FLAG_SEG 0x3000
#define BOOT_MEDIA_FLAG_OFF 0x101
#define BOOT_MEDIA_CD 1
.code16
.global start
start:
cli
xorw %ax, %ax
movw %ax, %ds
movw %ax, %ss
movw $0x7c00, %sp
# "You were booted from a CD." stage2main.c reads this to decide between
# ATA and ATAPI; without it the loader would read the kernel off whatever
# happens to be sitting at 0x1F0, which on a CD boot is usually nothing.
movw $BOOT_MEDIA_FLAG_SEG, %ax
movw %ax, %es
movw $BOOT_MEDIA_FLAG_OFF, %di
movb $BOOT_MEDIA_CD, %al
movb %al, %es:(%di)
# stage2.S expects zeroed segments and an inherited stack, same as it gets
# from bootasm.S.
xorw %ax, %ax
movw %ax, %es
ljmp $0, $STAGE2_ADDR