chalk-os/rustboot
1
0
Fork 0
Code Issues 2 Pull requests Projects Releases Packages Wiki Activity Actions

Support bios that expect a BPB being present #1

New issue
Open
opened 2025-05-06 18:15:13 +02:00 by mai-lapyst · 1 comment
mai-lapyst commented 2025-05-06 18:15:13 +02:00
Owner
Copy link

Some bios variants expect a BIOSPparameterBlock being present, which they also happily write inside thus screwing with the assembly in our bootsector.

Some bios variants expect a [**B**IOS**P**parameter**B**lock](https://en.wikipedia.org/wiki/BIOS_parameter_block) being present, which they also happily write inside thus screwing with the assembly in our bootsector.
mai-lapyst commented 2025-05-06 19:15:31 +02:00
Author
Owner
Copy link

Essentially blocked by the real realmode codegen problem since a BPB (or realisticly a EBPB) eats around 32 - 51 bytes (plus 3 bytes offset / initial jump), but currently we only have ~20 bytes wiggleroom.

Most of the bytes used tho are "useless" bc rust + LLVM try to encode everything in 32bit instructions where they perfectly fine could be 16bit ones (i.e. an 16bit value is mapped to an 32bit register and a 32bit move is used to load an 16bit immediate value into it...)

Essentially blocked by the real realmode codegen problem since a BPB (or realisticly a EBPB) eats around 32 - 51 bytes (plus 3 bytes offset / initial jump), but currently we only have ~20 bytes wiggleroom. Most of the bytes used tho are "useless" bc rust + LLVM try to encode everything in 32bit instructions where they perfectly fine could be 16bit ones (i.e. an 16bit value is mapped to an 32bit register and a 32bit move is used to load an 16bit immediate value into it...)
Sign in to join this conversation.
No Branch/Tag specified
Branches Tags
master
dev
No results found.
Labels
Clear labels
No items
No labels
Milestone
Clear milestone
No items
No milestone
Projects
Clear projects
No items
No project
Assignees
Clear assignees
No assignees
1 participant
Notifications
Due date
The due date is invalid or out of range. Please use the format "yyyy-mm-dd".

No due date set.

Depends on
#2 Figure out how we support real realmode codegen
chalk-os/rustboot
Reference: chalk-os/rustboot#1
No description provided.
Delete branch "%!s()"

Deleting a branch is permanent. Although the deleted branch may continue to exist for a short time before it actually gets removed, it CANNOT be undone in most cases. Continue?