nexoniarz/SchOS
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iso: a real EFI system partition, so a stick boots on strict firmware

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-isohybrid-gpt-basdat does nothing without an MBR template, so the ISO
had no partition table at all: written to a stick, it was a CD
filesystem at sector 0. AMI on a B550 (and OVMF) read El Torito off any
block device and booted it anyway. An HP all-in-one from 2012 looks for
an EFI system partition on a USB disk, as the spec says to, found none,
and listed the stick under Legacy only.

The FAT image now goes in a second time as MBR partition 2, type 0xEF,
and is FAT16 by cluster count rather than FAT12, the type old firmware
reads worst. Booted under OVMF both as a CD and as a USB disk. The ISO
also rebuilds when mkiso.sh changes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4
This commit is contained in:
Nexoniarz 2026-10-23 16:19:27 +02:00
commit 125663929a
2 changed files with 20 additions and 4 deletions
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Makefile
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@ -758,7 +758,7 @@ iso:
# One El Torito entry, pointing at a FAT image holding the loader and kernel.
# sysroot-install because the disc also carries the tree as a real hierarchy.
schos.iso: $(BUILD)/kernel/kernel $(BUILD)/uefi/BOOTX64.EFI sysroot-install
schos.iso: $(BUILD)/kernel/kernel $(BUILD)/uefi/BOOTX64.EFI tools/posix/mkiso.sh sysroot-install
SYSROOT=$(SYSROOT) sh tools/posix/mkiso.sh $@
# A partitioned disk -- GPT, an ESP and a SchFS partition -- which is what a