Fails on a real 486DX

[Treah]

Not sure where to put this issue but this procedure for creating a bootable bzImage to boot on a real 486 does not seam to work. I know it does however work on some 486 machines since ActionRetro was able to boot it on real hardware.. However when trying to boot this on my PackardBell CD12 with a 486DX processor at 66mhz I just get "Invalid Argument" when the kernel attempts to load.

[w84death]

Do this machine have at least 20MB of RAM?

[steelcowboy]

I'm noticing the same problem myself. I have a Compaq Presario CDS 524, 486DX processor with 40MB of RAM. However, when I boot it I don't see any errors only:

SYSLINUX 6.04 CHS 6.04-pre3-3-g05ac953c* Copyright (C) 1994-2015 H. Peter Anvin et al
[ BOOTING FLOPPINUX VERSION 0.3.1 1]
Loading bzImage... ok
Loading rootfs.cpio.xz... ok

And then it just hangs. My end goal is actually to have NetBSD on this machine but even that's not working, so in the meantime I'd love to help get floppinux booting if I can!

[w84death]

Thanks for report.

From what we see it is booting floppy and fully loading the kernel and file-system.

Next step should be starting actual Linux..

Hard to say without any error. I will think what can we do to try debug it.

[w84death]

Enable debugging in syslinux.cfg

DEFAULT floppinux
LABEL floppinux
SAY [ BOOTING FLOPPINUX VERSION 0.3.1 DEBUG ]
KERNEL bzImage
INITRD rootfs.cpio.xz
APPEND root=/dev/ram rdinit=/etc/init.d/rc console=tty0 ignore_loglevel earlyprintk=tty0 loglevel=8 tsc=unstable

Then replace that file on the floppy and try again.

[steelcowboy]

Gave that a try. I know it used the updated config as it said [ BOOTING FLOPPINUX VERSION 0.3.1 DEBUG ], but again there was no text after Loading rootfs.cpio.xz... ok

[w84death]

Grok suggests it could be a problem with XZ compression:

Step 1: Simplify the Initrd (Remove XZ Compression)
XZ is efficient but can fail silently on quirky 486 hardware. Switch to gzip, which is more universally supported.

In your filesystem/ directory:

• Recompress rootfs without XZ:

  find . | cpio -H newc -o | gzip > ../rootfs.cpio.gz
  cd ..
  

In syslinux.cfg, update:

DEFAULT floppinux
LABEL floppinux
SAY [ BOOTING FLOPPINUX VERSION 0.3.1 DEBUG GZ ]
KERNEL bzImage
INITRD rootfs.cpio.gz
APPEND root=/dev/ram rdinit=/etc/init.d/rc console=tty0 ignore_loglevel earlyprintk=tty0 loglevel=8 tsc=unstable

You will also need to remove XZ and add GZIP support in kernel (Library routines). I don't remember how bigger that was but should still fit into a floppy.

[Treah]

Yes my machine has 40mb of ram and I think I even tried using the normal compression instead of XZ and it still did not work. I know that the kernel maintainers did mention removing support for older platforms from the kernel so this may be why its no longer working as the kernel may require some processor routines missing from the 486.

What I am going to try and creating a bootable image and see If I am able to get it working on PCEM as that actually emulates the full processor and not just some of it like qemu does.

[SuperMaxusa]

I tested an image from the site on 86box and it boots on (partly) Socket 3 with Intel 486DX 50 MHz + 24 MB RAM.

Here are tested motherboards where Floppinux works:

• Compaq Presario 7100/7200 Series 486
• ASUS PVI-486SP3C
• AAEON SBC-490
• ASUS VL/I-486SV2GX4

I used default BIOS settings, sometimes changing the floppy drives settings to the correct ones. No idea what it caused this.

In syslinux.cfg, update: ...

Note to what Grok says, you also need to compile kernel with CONFIG_EARLY_PRINTK for earlyprintk.

[SuperMaxusa]

As far as I understand, Booting failed: Invalid Argument was displayed from syslinux side.

Looking in com32/elflink/ldlinux/kernel.c, if syslinux_boot_linux() return, it shows the error message. However, I didn't find the root of the problem yet.

On Alaris Cobalt LPX (86box), I got these logs from syslinux: alaris-86box.txt
Last lines:

Offset: 134656  lsector: 263
this_extent: lstart 263 pstart 2339 len 1
this_extent: lstart 263 pstart 2339 len 1
   I/O: inode 0x00448e20 @ 263 start 2339 len 1
CHS[00]: 1 @ 274877909283 (1/18/4096) 0000:11162d  0x001168e8
put_inode 0x00448e20 name rootfs.cpio.xz refcnt 0
put_inode 0x0034d070 name (null) refcnt 2
ok
Booting kernel failed: Invalid argument
boot:

On QEMU, I got these logs: i440fx-qemu.txt
Last lines:

Offset: 134656  lsector: 263
this_extent: lstart 263 pstart 2339 len 1
this_extent: lstart 263 pstart 2339 len 1
   I/O: inode 0x00448f30 @ 263 start 2339 len 1
CHS[00]: 1 @ 274877909283 (1/18/4096) 0000:11162d  0x001168e8
put_inode 0x00448f30 name rootfs.cpio.xz refcnt 0
put_inode 0x0034d180 name (null) refcnt 2
ok

If someone is interested, here is Floppinux build with syslinux debug logging enabled: floppinux_testing.img.gz (shows the log on the screen and COM1)

UPD: people on Hacker News say that syslinux relies on E820h for memory map, which is not supported on some motherboards.

[mikebdp2]

@Treah @steelcowboy I had exactly the same "hanging" problem while trying to use the stronger-than-usual filesystem compression parameters that could not be processed by Linux kernel for some reason (i.e. not enough RAM for the chosen dictionary/parameters, or simply an unsupported mode). For example, https://github.com/mikebdp2/floppinux-amd64net/blob/main/floppinux.md :

find . -print0 | LC_ALL="C" sort -z | cpio -0 -H newc -o --reproducible 2>/dev/null > ./../rootfs.cpio
strip-nondeterminism -t cpio -T 1770768000 ./../rootfs.cpio
xz --threads=1 --format=lzma --check=crc32 --lzma1=dict=64MiB,lc=3,lp=0,pb=2,mode=normal,nice=273,mf=bt4,depth=0 < ./../rootfs.cpio > ./../rootfs.cpio.lzma

• this works, however: if I replace lc=3 with lc=4, it helps me to win a few KBs but the resulting rootfs couldn't be decompressed by a kernel - same "hanging" problem. Btw according to my experience, while XZ gives better compression for a Linux kernel, actually it's better to use LZMA for rootfs filesystem because the archive's filesize is nearly the same while the decompression routine in Linux kernel is larger for LZMA rootfs, so XZ kernel + LZMA rootfs are smaller than XZ kernel + XZ rootfs:

- General Setup
  - Initial RAM filesystem and RAM disk (initramfs/initrd)
    - Original instruction: Support initial ramdisk/ramfs compressed using XZ (CONFIG_RD_XZ) and **uncheck everything else**
    - My instruction: Support initial ramdisk/ramfs compressed using LZMA (CONFIG_RD_LZMA) and **uncheck everything else** (LZMA overall is smaller here)
- Library routines
  - Original instruction: XZ decompression: CONFIG_DECOMPRESS_XZ (selected by RD_XZ && BLK_DEV_INITRD) and **uncheck everything under it**
  - My instruction: LZMA decompression: CONFIG_DECOMPRESS_LZMA (selected by RD_LZMA && BLK_DEV_INITRD) (LZMA overall is smaller here)

Maybe this LZMA is also better for older hardware (the next suspect is checking the CPU instructions)