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boot: the BIOS loader is gone

Browse source 
1449 lines of boot/bios/, tools/sign.pl and tools/padstage2.pl, plus the
build rules, the disk image and the ISO entry that existed to carry them.

Everything since roughly 2012 boots UEFI, and CSM -- the firmware-side
BIOS emulation that lets a legacy loader run on such a machine at all --
has been going away since Intel dropped support for it in 2020. So this
is not a path being retired early; it is one whose remaining hardware is
already the exception.

The cost was never the code, it was the tax on everything near it. Stage
2 had a 65-sector ceiling it overflowed silently -- 25440 bytes against
24576 -- and because the kernel is written at sector 1 + STAGE2_SECTORS,
an overflowing loader was overwritten by the very kernel it was loading.
The resolution list could not be shared with UEFI either: VBE mode
setting is INT 10h, so matching it needed unreal mode, which is the
riskiest code in the tree for a feature that already worked elsewhere.

What replaces schos.img is the staged ESP, handed to QEMU as a virtual
FAT volume. That is a development arrangement and not an installable
disk; a real GPT image with a real FAT partition is the installer's job,
and until it exists nothing here writes a disk a machine boots unaided.
Secure Boot is untouched too -- the loader is unsigned.

The ISO keeps one El Torito entry, the FAT image holding loader and
kernel. It never booted from a USB stick via BIOS anyway: the firmware
presents the stick as a hard disk while stage2main.c read the kernel back
over ATAPI.

The 32-bit multiboot entry in entry.S now has no caller and is left in
place. Deleting kernel entry code is its own change with its own way of
failing silently, and it should not ride along with this one.

Ported with it: run.ps1, the six screenshot tools, and schcom_test.sh,
each with its own OVMF varstore copy so no run inherits another's UEFI
variables.

Two things this shook out. OVMF now belongs in `all`: nothing boots
without firmware, `make clean` wipes build/ including the copy fetched
from the host, and a clean followed by a build left every run script
throwing. And it cannot be listed as a prerequisite at the top of the
file -- make expands prerequisites when it reads the line, and
$(OVMF_CODE) is defined further down, so naming it there appends nothing
and says nothing.

Verified from a clean tree: 110 [ok] and no failures on the full suite,
the ISO boots with no hard disk attached, schfs-check passes, schcom's
end-to-end pixel test passes, and fbshot captures a real 1280x800 frame.
This commit is contained in:
Nexoniarz 2026-08-11 10:20:28 +02:00
commit 651899220c
23 changed files with 317 additions and 1826 deletions
Download patch file Download diff file Expand all files Collapse all files

89
tools/windows/bootcheck.ps1
View file

@ -26,11 +26,8 @@ param(
# attached, which is the only way to prove the ISO is self-contained.
# Needs `make iso` first.
[switch]$Iso,
# Boot through OVMF instead of the BIOS loader. The disk layout is
# deliberately the same -- the staged ESP lands on index 0 and the SchFS
# volume on index 1 -- so every check below runs unaltered and a difference
# in the transcript is a difference in the *firmware path*, not in what was
# asked. Needs `make esp` first.
# Accepted and ignored. It used to select OVMF over the BIOS loader; there
# is only the one path now, so it names a choice that no longer exists.
[switch]$Uefi,
# Terminal behaviour: pipes, isatty, SIGPIPE, and Ctrl-C. None of these
# can be checked by looking at a screenshot, and all of them were broken
@ -86,7 +83,6 @@ if (-not $Qemu) { $Qemu = Find-Qemu }
$ErrorActionPreference = 'Stop'
# Repo root is two levels up: this script lives in tools/windows/.
$root = Split-Path (Split-Path $PSScriptRoot -Parent) -Parent
$hda = Join-Path $root 'schos.img'
# The root filesystem. SchFS is the only root there is, so this is not a
# choice -- a kernel handed anything else on device 1 panics in forkret().
$hdb = Join-Path $root 'build/schfs.img'
@ -249,73 +245,56 @@ $commands += 'echo MARKER-DONE'
$isoPath = Join-Path $root 'schos.iso'
if ($Iso -and -not (Test-Path $isoPath)) { throw "no $isoPath -- run 'make iso' first" }
$drives = if ($Uefi) {
# The varstore is written by the firmware, so each run gets its own copy.
# Sharing one would let a run that changed a UEFI variable -- boot order,
# console mode -- decide how the next run behaves, which is exactly the
# kind of dependency between runs that makes a suite stop being evidence.
# OVMF is not optional any more: the BIOS loader is gone, so every run boots
# through firmware. -Uefi is still accepted and does nothing, because it named
# a choice that no longer exists.
$code = Join-Path $root 'build/OVMF_CODE.fd'
$vars = Join-Path $root 'build/OVMF_VARS.fd'
foreach ($f in @($code, $vars)) {
if (-not (Test-Path $f)) { throw "no $f -- run 'make qemu-uefi' once to fetch OVMF" }
}
# The varstore is written by the firmware, so each run gets its own copy.
# Sharing one would let a run that changed a UEFI variable -- boot order,
# console mode -- decide how the next run behaves, which is exactly the kind of
# dependency between runs that makes a suite stop being evidence.
$runVars = Join-Path $root 'build/bootcheck-OVMF_VARS.fd'
Copy-Item -Force $vars $runVars
$firmware = @("-drive if=pflash,format=raw,unit=0,readonly=on,file=`"$code`""
"-drive if=pflash,format=raw,unit=1,file=`"$runVars`"")
$drives = if ($Iso) {
# No hard disk at all, so a kernel that still secretly depends on one fails
# here rather than in someone's optical drive.
$firmware + @("-cdrom `"$isoPath`"", '-boot d')
} else {
$esp = Join-Path $root 'build/esp'
if (-not (Test-Path (Join-Path $esp 'EFI/BOOT/BOOTX64.EFI'))) {
throw "no staged ESP at $esp -- run 'make esp' first"
}
$code = Join-Path $root 'build/OVMF_CODE.fd'
$vars = Join-Path $root 'build/OVMF_VARS.fd'
foreach ($f in @($code, $vars)) {
if (-not (Test-Path $f)) { throw "no $f -- run 'make qemu-uefi' once to fetch OVMF" }
}
$runVars = Join-Path $root 'build/bootcheck-OVMF_VARS.fd'
Copy-Item -Force $vars $runVars
@("-drive if=pflash,format=raw,unit=0,readonly=on,file=`"$code`""
"-drive if=pflash,format=raw,unit=1,file=`"$runVars`""
"-drive file=fat:rw:`"$esp`",index=0,media=disk"
"-drive file=`"$hdb`",format=raw,index=1,media=disk")
} elseif ($Iso) {
@("-cdrom `"$isoPath`"", '-boot d')
} else {
@("-drive file=`"$hda`",format=raw,index=0,media=disk"
"-drive file=`"$hdb`",format=raw,index=1,media=disk")
$firmware + @("-drive file=fat:rw:`"$esp`",index=0,media=disk"
"-drive file=`"$hdb`",format=raw,index=1,media=disk")
}
$psi = New-Object System.Diagnostics.ProcessStartInfo
$psi.FileName = $Qemu
$usbDevices = if ($Usb) {
# One device of each speed class QEMU can produce: usb-storage negotiates
# SuperSpeed on qemu-xhci, the HID devices come up high speed. They take
# different paths through enumeration -- a USB3 port arrives already
# enabled and a USB2 port has to be reset first -- so one of each is the
# difference between testing the driver and testing half of it.
@('-device qemu-xhci,id=xhci'
'-device usb-kbd,bus=xhci.0'
# The mouse goes behind a hub, so the tree is a tree and not a row of
# root ports. That exercises the route string, the hub's own slot
# context, and the transaction translator -- none of which a device
# plugged straight into the controller touches at all.
# QEMU places a device under a hub by port *path*, not by a child bus:
# the hub sits on port 2 and the mouse on port 2.1 of the same bus.
'-device usb-hub,id=hub,bus=xhci.0,port=2'
'-device usb-mouse,bus=xhci.0,port=2.1'
# Its own small image, never $hdb. The checks below read a v1 superblock
# off this stick and assert on its sector count and size field, so the
# stick has to be a v1 image whatever the root filesystem is -- under
# the root $hdb is a SchFS volume and those fields are simply not
# there, which failed three USB checks that had nothing wrong with USB.
# It also stops the same file being attached twice, once as the root
# disk and once as a USB device.
"-drive id=usbstick,file=`"$(Join-Path $root 'build/usbstick.img')`",format=raw,if=none"
'-device usb-storage,bus=xhci.0,drive=usbstick')
} else { @() }
# The USB run needs the QEMU monitor, because `sendkey` is the only way to
# press a key on an emulated USB keyboard -- typing on stdin goes to the
# serial port and proves nothing about USB.
# Ask the OS for a free port rather than hardcoding one. A run that dies
# before its `finally` leaves QEMU holding the old number, and every later run
# then fails with "Failed to find an available port" -- which looks like a
# bug in whatever is being tested rather than in the harness.
# A free loopback port, found by binding one and letting go. Hardcoding it made
# two runs on one machine collide.
$monPort = if ($Usb -or $Evdev) {
$l = [System.Net.Sockets.TcpListener]::new([System.Net.IPAddress]::Loopback, 0)
$l.Start(); $p = $l.LocalEndpoint.Port; $l.Stop(); $p
$l.Start(); $mp = $l.LocalEndpoint.Port; $l.Stop(); $mp
} else { 0 }
$monitor = if ($Usb -or $Evdev) { @("-monitor tcp:127.0.0.1:$monPort,server,nowait") } else { @() }
$psi.Arguments = ($drives + $usbDevices + $monitor + @(
@ -327,9 +306,7 @@ $psi.Arguments = ($drives + $usbDevices + $monitor + @(
$psi.RedirectStandardInput = $true
$psi.UseShellExecute = $false
$what = if ($Uefi) { "OVMF, hdb = $(Split-Path $hdb -Leaf)" }
elseif ($Iso) { 'schos.iso, no hard disk' }
else { "hdb = $(Split-Path $hdb -Leaf)" }
$what = if ($Iso) { 'schos.iso, no hard disk' } else { "hdb = $(Split-Path $hdb -Leaf)" }
Write-Host "==> booting ($what)" -ForegroundColor Cyan
$p = [System.Diagnostics.Process]::Start($psi)
# Recorded immediately, so that a run killed one instruction later is still

19
tools/windows/crashshot.ps1
View file

@ -45,7 +45,20 @@ if (-not $Qemu) { $Qemu = Find-Qemu }
$ErrorActionPreference = 'Stop'
# Repo root is two levels up: this script lives in tools/windows/.
$root = Split-Path (Split-Path $PSScriptRoot -Parent) -Parent
$hda = Join-Path $root 'schos.img'
$esp = Join-Path $root 'build/esp'
# OVMF and the staged ESP, because there is one boot path now. The old
# schos.img was a raw disk with the boot sector at LBA 0 -- a layout only the
# BIOS loader could use, and it went with it.
$code = Join-Path $root 'build/OVMF_CODE.fd'
$vars = Join-Path $root 'build/OVMF_VARS.fd'
foreach ($f in @($code, $vars)) {
if (-not (Test-Path $f)) { throw "no $f -- run 'make qemu-uefi' once to fetch OVMF" }
}
if (-not (Test-Path (Join-Path $esp 'EFI/BOOT/BOOTX64.EFI'))) {
throw "no staged ESP at $esp -- run 'make esp' first"
}
$runVars = Join-Path $root "build/crashshot-OVMF_VARS.fd"
Copy-Item -Force $vars $runVars
# The root filesystem. SchFS is the only root there is: the kernel mounts
# device 1 in forkret() and panics if it is not a SchFS volume, so this is
# not a choice and there is no -SchFS switch any more. It used to default to
@ -65,7 +78,9 @@ $monPort = 55555
$psi = New-Object System.Diagnostics.ProcessStartInfo
$psi.FileName = $Qemu
$psi.Arguments = @(
"-drive file=`"$hda`",format=raw,index=0,media=disk"
"-drive if=pflash,format=raw,unit=0,readonly=on,file=`"$code`""
"-drive if=pflash,format=raw,unit=1,file=`"$runVars`""
"-drive file=fat:rw:`"$esp`",index=0,media=disk"
"-drive file=`"$hdb`",format=raw,index=1,media=disk"
'-m 1G -smp 1 -cpu qemu64,+rdtscp -machine pc-i440fx-9.2'
'-display none'

19
tools/windows/dispshot.ps1
View file

@ -50,7 +50,20 @@ if (-not $Qemu) { $Qemu = Find-Qemu }
$ErrorActionPreference = 'Stop'
# Repo root is two levels up: this script lives in tools/windows/.
$root = Split-Path (Split-Path $PSScriptRoot -Parent) -Parent
$hda = Join-Path $root 'schos.img'
$esp = Join-Path $root 'build/esp'
# OVMF and the staged ESP, because there is one boot path now. The old
# schos.img was a raw disk with the boot sector at LBA 0 -- a layout only the
# BIOS loader could use, and it went with it.
$code = Join-Path $root 'build/OVMF_CODE.fd'
$vars = Join-Path $root 'build/OVMF_VARS.fd'
foreach ($f in @($code, $vars)) {
if (-not (Test-Path $f)) { throw "no $f -- run 'make qemu-uefi' once to fetch OVMF" }
}
if (-not (Test-Path (Join-Path $esp 'EFI/BOOT/BOOTX64.EFI'))) {
throw "no staged ESP at $esp -- run 'make esp' first"
}
$runVars = Join-Path $root "build/dispshot-OVMF_VARS.fd"
Copy-Item -Force $vars $runVars
# The root filesystem. SchFS is the only root there is: the kernel mounts
# device 1 in forkret() and panics if it is not a SchFS volume, so this is
# not a choice and there is no -SchFS switch any more. It used to default to
@ -70,7 +83,9 @@ $monPort = 55555
$psi = New-Object System.Diagnostics.ProcessStartInfo
$psi.FileName = $Qemu
$psi.Arguments = @(
"-drive file=`"$hda`",format=raw,index=0,media=disk"
"-drive if=pflash,format=raw,unit=0,readonly=on,file=`"$code`""
"-drive if=pflash,format=raw,unit=1,file=`"$runVars`""
"-drive file=fat:rw:`"$esp`",index=0,media=disk"
"-drive file=`"$hdb`",format=raw,index=1,media=disk"
'-m 1G -smp 1 -cpu qemu64,+rdtscp -machine pc-i440fx-9.2'
'-display none'

19
tools/windows/fbshot.ps1
View file

@ -44,7 +44,20 @@ if (-not $Qemu) { $Qemu = Find-Qemu }
$ErrorActionPreference = 'Stop'
# Repo root is two levels up: this script lives in tools/windows/.
$root = Split-Path (Split-Path $PSScriptRoot -Parent) -Parent
$hda = Join-Path $root 'schos.img'
$esp = Join-Path $root 'build/esp'
# OVMF and the staged ESP, because there is one boot path now. The old
# schos.img was a raw disk with the boot sector at LBA 0 -- a layout only the
# BIOS loader could use, and it went with it.
$code = Join-Path $root 'build/OVMF_CODE.fd'
$vars = Join-Path $root 'build/OVMF_VARS.fd'
foreach ($f in @($code, $vars)) {
if (-not (Test-Path $f)) { throw "no $f -- run 'make qemu-uefi' once to fetch OVMF" }
}
if (-not (Test-Path (Join-Path $esp 'EFI/BOOT/BOOTX64.EFI'))) {
throw "no staged ESP at $esp -- run 'make esp' first"
}
$runVars = Join-Path $root "build/fbshot-OVMF_VARS.fd"
Copy-Item -Force $vars $runVars
# The root filesystem. SchFS is the only root there is: the kernel mounts
# device 1 in forkret() and panics if it is not a SchFS volume, so this is
# not a choice and there is no -SchFS switch any more. It used to default to
@ -60,7 +73,9 @@ $monPort = 55556 # not crashshot's 55555, so the two can run back to back
$psi = New-Object System.Diagnostics.ProcessStartInfo
$psi.FileName = $Qemu
$psi.Arguments = @(
"-drive file=`"$hda`",format=raw,index=0,media=disk"
"-drive if=pflash,format=raw,unit=0,readonly=on,file=`"$code`""
"-drive if=pflash,format=raw,unit=1,file=`"$runVars`""
"-drive file=fat:rw:`"$esp`",index=0,media=disk"
"-drive file=`"$hdb`",format=raw,index=1,media=disk"
'-m 1G -smp 1 -cpu qemu64,+rdtscp -machine pc-i440fx-9.2'
'-display none'

19
tools/windows/splashshot.ps1
View file

@ -55,7 +55,20 @@ Remove-Item -Recurse -Force $dir -ErrorAction SilentlyContinue
New-Item -ItemType Directory -Force $dir | Out-Null
Remove-Item -Force $log -ErrorAction SilentlyContinue
$hda = Join-Path $root 'schos.img'
$esp = Join-Path $root 'build/esp'
# OVMF and the staged ESP, because there is one boot path now. The old
# schos.img was a raw disk with the boot sector at LBA 0 -- a layout only the
# BIOS loader could use, and it went with it.
$code = Join-Path $root 'build/OVMF_CODE.fd'
$vars = Join-Path $root 'build/OVMF_VARS.fd'
foreach ($f in @($code, $vars)) {
if (-not (Test-Path $f)) { throw "no $f -- run 'make qemu-uefi' once to fetch OVMF" }
}
if (-not (Test-Path (Join-Path $esp 'EFI/BOOT/BOOTX64.EFI'))) {
throw "no staged ESP at $esp -- run 'make esp' first"
}
$runVars = Join-Path $root "build/splashshot-OVMF_VARS.fd"
Copy-Item -Force $vars $runVars
# The root filesystem. SchFS is the only root there is: the kernel mounts
# device 1 in forkret() and panics if it is not a SchFS volume, so this is
# not a choice and there is no -SchFS switch any more. It used to default to
@ -75,7 +88,9 @@ $psi.Arguments = @(
# first fix and it meant duplicating build/fs.img, all 153 MB of it, on
# every run. -snapshot keeps writes in a temporary overlay, so the originals
# are untouched either way.
"-drive file=`"$hda`",format=raw,index=0,media=disk,file.locking=off"
"-drive if=pflash,format=raw,unit=0,readonly=on,file=`"$code`""
"-drive if=pflash,format=raw,unit=1,file=`"$runVars`""
"-drive file=fat:rw:`"$esp`",index=0,media=disk"
"-drive file=`"$hdb`",format=raw,index=1,media=disk,file.locking=off"
'-snapshot'
'-m 1G -smp 1 -cpu qemu64,+rdtscp -machine pc-i440fx-9.2'

19
tools/windows/textshot.ps1
View file

@ -50,7 +50,20 @@ if (-not $Qemu) { $Qemu = Find-Qemu }
$ErrorActionPreference = 'Stop'
# Repo root is two levels up: this script lives in tools/windows/.
$root = Split-Path (Split-Path $PSScriptRoot -Parent) -Parent
$hda = Join-Path $root 'schos.img'
$esp = Join-Path $root 'build/esp'
# OVMF and the staged ESP, because there is one boot path now. The old
# schos.img was a raw disk with the boot sector at LBA 0 -- a layout only the
# BIOS loader could use, and it went with it.
$code = Join-Path $root 'build/OVMF_CODE.fd'
$vars = Join-Path $root 'build/OVMF_VARS.fd'
foreach ($f in @($code, $vars)) {
if (-not (Test-Path $f)) { throw "no $f -- run 'make qemu-uefi' once to fetch OVMF" }
}
if (-not (Test-Path (Join-Path $esp 'EFI/BOOT/BOOTX64.EFI'))) {
throw "no staged ESP at $esp -- run 'make esp' first"
}
$runVars = Join-Path $root "build/textshot-OVMF_VARS.fd"
Copy-Item -Force $vars $runVars
# The root filesystem. SchFS is the only root there is: the kernel mounts
# device 1 in forkret() and panics if it is not a SchFS volume, so this is
# not a choice and there is no -SchFS switch any more. It used to default to
@ -70,7 +83,9 @@ $monPort = 55555
$psi = New-Object System.Diagnostics.ProcessStartInfo
$psi.FileName = $Qemu
$psi.Arguments = @(
"-drive file=`"$hda`",format=raw,index=0,media=disk"
"-drive if=pflash,format=raw,unit=0,readonly=on,file=`"$code`""
"-drive if=pflash,format=raw,unit=1,file=`"$runVars`""
"-drive file=fat:rw:`"$esp`",index=0,media=disk"
"-drive file=`"$hdb`",format=raw,index=1,media=disk"
'-m 1G -smp 1 -cpu qemu64,+rdtscp -machine pc-i440fx-9.2'
'-display none'

19
tools/windows/ttyshot.ps1
View file

@ -43,7 +43,20 @@ if (-not $Qemu) { $Qemu = Find-Qemu }
$ErrorActionPreference = 'Stop'
# Repo root is two levels up: this script lives in tools/windows/.
$root = Split-Path (Split-Path $PSScriptRoot -Parent) -Parent
$hda = Join-Path $root 'schos.img'
$esp = Join-Path $root 'build/esp'
# OVMF and the staged ESP, because there is one boot path now. The old
# schos.img was a raw disk with the boot sector at LBA 0 -- a layout only the
# BIOS loader could use, and it went with it.
$code = Join-Path $root 'build/OVMF_CODE.fd'
$vars = Join-Path $root 'build/OVMF_VARS.fd'
foreach ($f in @($code, $vars)) {
if (-not (Test-Path $f)) { throw "no $f -- run 'make qemu-uefi' once to fetch OVMF" }
}
if (-not (Test-Path (Join-Path $esp 'EFI/BOOT/BOOTX64.EFI'))) {
throw "no staged ESP at $esp -- run 'make esp' first"
}
$runVars = Join-Path $root "build/ttyshot-OVMF_VARS.fd"
Copy-Item -Force $vars $runVars
# The root filesystem. SchFS is the only root there is: the kernel mounts
# device 1 in forkret() and panics if it is not a SchFS volume, so this is
# not a choice and there is no -SchFS switch any more. It used to default to
@ -73,7 +86,9 @@ $commands = @(
$psi = New-Object System.Diagnostics.ProcessStartInfo
$psi.FileName = $Qemu
$psi.Arguments = @(
"-drive file=`"$hda`",format=raw,index=0,media=disk"
"-drive if=pflash,format=raw,unit=0,readonly=on,file=`"$code`""
"-drive if=pflash,format=raw,unit=1,file=`"$runVars`""
"-drive file=fat:rw:`"$esp`",index=0,media=disk"
"-drive file=`"$hdb`",format=raw,index=1,media=disk"
'-m 1G -smp 1 -cpu qemu64,+rdtscp -machine pc-i440fx-9.2'
'-display none'