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WDe and GPT, booting DOS (Users)

posted by ecm Homepage E-mail, Düsseldorf, Germany, 04.01.2023, 13:42

> > > ... many many things mentioned ...
>
>
>
> It is not immediately clear to me if you have successfully booted FreeDOS
> from a GPT partition.
I have booted the FreeDOS kernel using my loaders (ldosboot boot sector loaders or bootable lDebug loader command) from a FAT12, FAT16, or FAT32 partition on a diskette (unpartitioned) or MBR-partitioned. I have no interest at this time to load from a GPT-partitioned unit.

> I am assuming Japheth's method for MS-DOS 7.1 on GPT could be reconfigured
> for FreeDOS on GPT (I hope that this can be achieved).
This is certainly possible. However, you will need to understand the involved memory layout and load protocols quite well to adapt this.


> Any pointers, etc you can offer would be greatly appreciated. It would
> take me a long time to fully understand all you have mentioned on this
> topic.
You're still "reading 4 sectors of KERNEL.SYS". This is wrong, you need to load the entire KERNEL.SYS file. And as mentioned you have to relocate your loader to make space for the kernel, which you did not do at all yet. And you should use the FAT to follow the chain of the kernel file, not assume that its data is contiguous (unfragmented). (The loader you're working on does have a "get next cluster" function for walking the FAT32 root directory's chain, already. That can be used to walk the chain of a file, too.)

Further, you're still checking for the "MZ" and "BJ" signatures of the kernel file. These signatures are generally not found in the FreeDOS kernel file (unless it is a multi-format file like my kernels/debuggers), so checking for them is wrong here.

Also, you changed the "db 0EAh" far immediate jump to jump to 60h:200h. This is wrong, as I already wrote the entrypoint is at 60h:0.

SI:DI need not be set for loading a FreeDOS kernel format file, though they do not harm anything either. Your comments on them are wrong however.


I did not check the device driver (CONFIG.SYS) component of this yet. However, the above errors are certainly present in the pre-kernel stage.

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l

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