https://github.com/farlepet/lboot

x86 bootloader
https://github.com/farlepet/lboot

Last synced: 10 months ago
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x86 bootloader

• Host: GitHub
• URL: https://github.com/farlepet/lboot
• Owner: farlepet
• License: mit
• Created: 2022-07-31T01:23:28.000Z (over 3 years ago)
• Default Branch: master
• Last Pushed: 2022-10-08T21:27:25.000Z (about 3 years ago)
• Last Synced: 2025-01-11T22:20:39.512Z (12 months ago)
• Language: C
• Size: 237 KB
• Stars: 2
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
LBoot

=====

x86 bootloader for floppy disks. For a working example of LBoot being used, see

[Lambda OS](https://github.com/farlepet/lambda-os).

![Screenshot of LBoot boot loading kernel](docs/lboot.jpg)

Current Support

---------------

 - Filesystems

   - FAT12

     - Limited to the boot device

     - No long filename support

 - Serial transfer protocols

   - XMODEM

 - Kernel Format

   - ELF

 - Multiboot 2 (optional)

   - `CMDLINE`

   - `BOOTLOADER_NAME`

   - `MODULE`

   - `BASIC_MEMINFO`

   - `MMAP`

   - `ACPI_OLD`

   - `ACPI_NEW`

 - Outputs

   - VGA

   - Serial

Features can be toggled via `inc/config.h`. Stage 2 size based on features:

 - All features disabled:      ~20 KiB

 - With all features:          ~23 KiB

 - With all debugging enabled: ~25 KiB

Future Work

-----------

 - Loading kernel via Kermit

 - Flat binary support

 - Kernel relocation support (maybe)

 - Look into adding minimal FAT12 support to stage 1 loader

   - Currently this is leveraging an additional tool (`sector_mapper`) to

     generate a list of sectors to load for stage 2. This makes writing/updating

     the bootloader to the floppy more complicated than is probably necessary.

   - Simply giving the stage 1 loader the first sector of the stage 2 file

     would probably be sufficient.

Building

--------

Requirements:

 - `make`

 - `gcc` or `clang`

 - `mtools` for generating floppy image

To build, simply run `make` in the main directory. This will generate a `boot.img`

file containing the bootloader. A configuration and kernel file will need to be

provided.

To write the bootloader to an existing floppy disk or image, use the following from

within the root of the repository:

```

tools/lboot_prepare.sh 

```

Testing

-------

LBoot has been tested both within QEMU, and on a Compaq Armada 1700, booting the

[Lambda Kernel](https://github.com/farlepet/lambda-kern)

Config

------

LBoot is configured using a text file (currently must be named LBOOT.CFG in the

LBOOT directory of the boot filesystem). The syntax is simple, but somewhat

strict. Each configuration line is a key-value pair separated by a `=`. There

must be no spaces on either side of the `=`, and lines not containing a `=` are

effectively comments.

The following are the currently supported set of configuration keys:

 - `CFGVER`: Config version, must be 1

 - `KERNEL`: Kernel file to load

 - `CMDLINE`: Commandline to pass to kernel

 - `MODULE`: File to load as a module.

   - Each instance will add a new module, currently up to 4 are supported.

Files can be any of the following:

 - Plain filename - Attempts to find the file on the boot filesystem

 - `xmodem://COMx` - Loads file via XMODEM, where x is the serial port to use, 1-4