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boot: separate BIOS from UEFI

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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.
This commit is contained in:
Nexoniarz 2026-08-09 16:00:03 +02:00
commit 08a1a9033a
19 changed files with 125 additions and 33 deletions
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2
tools/posix/mkiso.sh
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@ -22,7 +22,7 @@
# is that stage2main.c reads the kernel back with ATAPI instead of ATA.
#
# STAGE2_SECTORS comes from the environment, set by the Makefile, because this
# same number also lives in boot/bootasm.S, boot/stage2main.c and the dd offsets
# same number also lives in boot/bios/bootasm.S, boot/bios/stage2main.c and the dd offsets
# in schos.img's recipe. It was previously written out by hand in three
# separate spots in this file alone, and raising it for the boot logo is what
# turned that from a latent hazard into a broken image.

2
tools/windows/bootcheck.ps1
View file

@ -468,7 +468,7 @@ if ($gens.Count -ge 2 -and
if ($Fb) {
Expect 'id\s+schosfb' 'FBIOGET_FSCREENINFO identifies the device'
# 800x600 is what boot/stage2.S asks VBE for. Asserting the numbers rather
# 800x600 is what boot/bios/stage2.S asks VBE for. Asserting the numbers rather
# than just "the ioctl returned" is the point: the old code path returned
# success with an untouched buffer, i.e. a 0x0 screen.
Expect '(?m)^xres\s+800' 'the reported width is the mode actually set'