08a1a9033a
boot/bios/ now holds the MBR, the El Torito stub and the real-mode stage 2; boot/uefi/ is empty and documented. Separate directories rather than #ifdefs, because the two share almost nothing. A BIOS loader lives in 16-bit real mode, reaches the firmware through software interrupts, and walks itself up into long mode. A UEFI loader is a 64-bit PE that the firmware has already placed in long mode with paging on, calling services through a table of function pointers. What they do share is the hand-off contract, which boot/README.md now writes down: ELF segments placed, long mode, a 24-byte-entry memory map at E820_MAP_ADDR, framebuffer geometry at VBE_INFO_ADDR. That contract is the point of documenting it now. UEFI's GetMemoryMap returns EFI_MEMORY_DESCRIPTORs, and the right move is to translate them into the entries kernel/arch/x86_64/e820.c already parses rather than teach the kernel a second format. Build output paths under $(BUILD)/boot are unchanged; only sources moved.
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| name | description | metadata | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| schunix-boot-splash-logo | The boot logo pipeline, why the loader draws it rather than the kernel, and the STAGE2_SECTORS trap that consolidating it exposed. |
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The boot splash shows the Assets/Schunix Small Logo.png mark (an SX monogram in
a ring) above the S C H U N I X wordmark and its accent rule, all centred as
one group. Verified rendering correctly on 2026-08-08.
The logo is drawn by the bootloader, not the kernel. This is the
counter-intuitive part and it is a timing fact, not a preference: the kernel does
not reach vga_init() until roughly the last 300ms of a ~2.8s boot, so a
kernel-drawn logo appeared for about one frame before console_takeover() wiped
it. Drawn from splash() in boot/bios/stage2main.c it is up for the whole boot.
kernel/dev/vga.c keeps the same drawing code against the same mask
(vga_draw_logo, vga_logo_centered) for things that want the mark after
boot — the crash screen, eventually schinit. Don't "fix" the duplication by
deleting the loader's copy.
Pipeline: tools/mklogo.py (host Python, has its own PNG inflate +
un-filter) crops to the mark, box-downscales, normalises to full strength, packs
to a 4-bit coverage mask, and writes include/logo.h. Run make logo — it is
not a build dependency, and include/logo.h is committed, on the same
reasoning as include/font.h. The mask is coverage, not colour, so the palette
stays in schunix-console-tty's include/theme.h; the loader composites it in
SCH_FG because the source art is a silver gradient and the accent is reserved
for the one rule. 4 bits rather than 8 because the header is included by the
bootloader, where size is a boot constraint.
STAGE2_SECTORS was encoded in five places, not the three docs/layout.md
claimed. Raising it 24 → 48 to fit the 8 KiB mask proved it: the dd seek=25
offset stayed behind and the kernel got written straight over stage2's tail.
The five were boot/bios/bootasm.S, boot/bios/stage2main.c, the dd seek=, and twice
inside tools/mkiso.sh (its size assertion and -boot-load-size). It now lives
only in the root Makefile, which passes -DSTAGE2_SECTORS and exports it to
mkiso; the #defines left in the boot sources are #ifndef fallbacks. Hard
ceiling is 65 sectors — stage2 loads at 0x7E00 and must not reach the
multiboot kernel-search buffer at 0x10000 — and stage2main.c now
static-asserts that. See also schunix-iso-boot.
tools/splashshot.ps1 captures a burst of QEMU screendumps across early
boot and reports each frame's distinct-colour count, because the splash window
is too short to hit with a single guessed delay. It uses -snapshot plus
file.locking=off so it runs while an interactive QEMU has the images open —
booting from copies also works but means duplicating all 153 MB of
build/fs.img per run. Colour counts are the
assertion: ~2 means text console or blank, 18 means the 4bpp logo is up. If it
ever reads 156 again, something is drawing an 8-bit mask.
Two traps, both hit while doing this:
$(shell expr $(N) \* 512)in a Makefile does not work — make passes the backslash through, sh globs the*, and expr receives a directory listing. Make silently carries on with nonsense. Use$$(( ))in the recipe.make isowas failing when this was written, for unrelated reasons since fixed — see schunix-ramdisk-root-sizing.-boot-load-size 49is now verified: the ISO boots from optical media only.