| Filename | Latest commit message | Latest commit date |
|---|---|---|
35ea398334
The first piece of real-hardware work, and it is three bugs that QEMU cannot show you. The report was an ASUS laptop -- Ryzen 7000-series APU, Radeon integrated, RTX discrete -- booting to a white underscore on a black screen, and unable to be offered 1920x1080. **The framebuffer address was truncated.** The loader handed over `(UINT32)gop->Mode->FrameBufferBase` and the kernel read a 32-bit field out of a VBE mode-info block -- a *BIOS* structure the UEFI path had been filling in because the kernel already knew how to read one. A machine that puts its aperture above 4 GB, which is ordinary on a laptop with a discrete GPU, got a plausible-looking address pointing at nothing. The splash went into it, the kernel was handed it, and the firmware's own cursor kept blinking on an otherwise black screen. Every step in that sequence succeeded on a number that was wrong, which is why there is no error message anywhere in it. SCHBOOT_FB_BASE is the loader's own display block: 64-bit address, 64-bit size, 32-bit width, height and stride, and the pixel format. The VBE block is still written for the BIOS loader, but anything that does not fit is left at zero rather than wrapped -- a truncated address is this bug, and a zero is at least honest. The kernel then has a problem the loader does not: its direct map covers the low 4 GB, so a framebuffer above it needs ioremap(), which needs kpdpt, which kvmalloc() has not allocated when the early console starts. A low framebuffer is attached exactly as before; a high one is attached immediately after kvmalloc(), still thousands of lines before anything else. **There was more than one adapter, and the first one was taken.** LocateProtocol answers with *a* GOP and the specification says nothing about which. QEMU with a stdvga and a virtio-gpu has **three** handles and two of them are Blt-only with a framebuffer address of zero -- so this is not a hardware-only hazard, it was a one-in-three chance of drawing into address 0 that happened to keep coming up heads. Every handle is scored now: no aperture, no candidacy; a readable current mode beats one that needs changing; size breaks the tie. **mode_usable() rejected modes real machines have.** A padded scanline (every GPU that aligns its rows -- and very likely the reason 1920x1080 could not be offered), a width not divisible by eight (1366x768, which is half the laptops in the world), and anything below 800x600 (the only mode some firmware gives over a KVM). All three passed on QEMU, which is why they survived. The mode list now offers 1366x768 and 640x480 where it did not. The loader also prints what it found, to the firmware's text console, which is cleared before the splash: invisible on a boot that works, and the only thing on the screen on a boot that dies before the splash. One process note, recorded because it cost a wrong test: `make UEFI_KEEP=1` ships the loader that is already built. Its own comment says "a build that quietly ships a stale bootloader is how you spend an evening debugging code that is not running", and that is exactly what happened -- a regression run that looked clean had tested the old loader. Loader work gets a full build. Both supported configurations verified after a clean build: one boot each, no traps, no panics, socktest and memfdtest green, and the adapter report shows the right one being chosen out of three. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> |
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| .. | ||
| architecture | ||
| branding | ||
| guides | ||
| history | ||
| niveus | ||
| plan | ||
| Website | ||
| licensing.md | ||
| README.md | ||
SchOS documentation
Four kinds of document, kept in four directories, because they answer four different questions and go stale at four different rates.
| architecture/ | What SchOS is | Present tense. Describes what is built and working. |
| plan/ | What SchOS will be | Future tense. Everything here is unbuilt. |
| guides/ | How to work on it | Imperative. Build it, test it, add to it. |
| history/ | Why it is the way it is | Past tense. Bugs whose cause is not visible from the fix. |
Plus two that belong to no category and apply to everything: licensing.md — read it before copying anyone else's code in — and branding/, which holds the marks and the rules for using them.
The rule that keeps this from rotting
When something is finished, it moves from
plan/toarchitecture/and is rewritten as a description of the thing rather than a record of building it.
A completed item is not a ticked checkbox. A ticked checkbox says the work happened; it does not say what the work produced, and six months later the checkbox is the only thing left and it explains nothing.
So finishing a piece of work has three steps, and the third is not optional:
- The code works and is tested.
- The plan entry is deleted.
- A description exists in
architecture/written for somebody who was not there — what it does, what shape it has, what it costs, and what it still does not do.
This is not bookkeeping. The tree has already proved it necessary: the network stack was finished, verified end to end, and for a month afterwards the only description of it anywhere was a checkbox in a roadmap, four levels of indentation deep, written in the past tense of somebody arguing for the work rather than explaining the result.
The "what it does not do" section is the one that pays. Every description in
architecture/ ends with one. A document that only lists a subsystem's
strengths is marketing, and the reader who most needs the document is the one
about to trip over a limitation nobody wrote down.
Start here
New to the tree → architecture/README.md, the system layer by layer, then guides/layout.md for where the files are.
Trying to build it → guides/building.md.
Wondering what happens next → plan/1.0.md, which is the finish line and the register of everything half-built. Then plan/README.md for the order.
About to start something new → the register, first. Nothing new starts while it has rows in it, and a row leaves only by being finished or deleted.
Something is broken and it feels familiar → history/. There is a good chance it is in there.
architecture/ — what SchOS is
| README | The system, layer by layer. Read first. |
| boot.md | Firmware to the first userspace process. |
| kernel.md | SchIFT: memory, processes, scheduling, traps, signals, SMP. |
| syscalls.md | The call table, and the Linux personality that lets real software run. |
| filesystem.md | The VFS, the buffer cache, procfs, mounts. |
| schfs.md | SchFS: the copy-on-write root filesystem. |
| devices.md | The device model, driver binding, the class vtables. |
| usb.md | xHCI, the USB core, and the class drivers. |
| graphics.md | Framebuffer, text rendering, console, and the crash screen. |
| terminals.md | The six virtual terminals, and how one is switched to. |
| networking.md | Drivers, lwIP, sockets — Unix and INET. |
| init.md | schinit, PID 1 as a role, and the job manifests. |
plan/ — what SchOS will be
| README | The three current decisions and the order they happen in. |
| 1.0.md | The finish line, and the freeze. What 1.0 contains, what is deferred, and the register of every half-built thing in the tree. |
| foundations.md | The kernel work everything else is blocked on. |
| wayland.md | The GUI stack, and what gets deleted to make room. |
| hybrid.md | Moving drivers out of the kernel. |
| schapi.md | The long-term API layering, and the compatibility promise. |
| roadmap.md | Everything else still open. |
guides/ — how to work on it
| building.md | Prerequisites and the build, per host. |
| testing.md | The harnesses, and what each one actually proves. |
| layout.md | Repository map, and how to add a program or a port. |
| adding-a-driver.md | Writing one, binding it, publishing its class vtable. |
branding/ — the marks
| README | Shift, the one mark: what it is for, the colour rule, why an icon and a mascot were removed, and why a raster is committed next to its SVG. |
history/ — why it is the way it is
| README | What belongs in here and what does not. |
| kernel.md | Bugs whose cause was nowhere near their symptom. |
| schfs.md | The filesystem's own, from the same period as its design. |
| moving-to-linux.md | The Windows-to-Fedora move, kept for the parts that recur. |
Writing one of these
Four conventions, all of them observable in the existing files:
State the cost. Every design choice gave something up. A document that does not say what is a document that will be argued with later by somebody who only sees the downside.
Prefer the measured number to the remembered one. "500 of 3565 files carry the advertising clause" is worth more than "some do", and it was worth the minute it took to count.
Write down the bug that shaped it. Half the non-obvious code in this tree is non-obvious because something failed once. If a design is strange, the strangeness is load-bearing and the reader deserves to know why before changing it.
No dates in headings. A date in a heading turns a description into a
changelog, and the description is the thing with a long life. Dates belong in
history/, where they mean something.