Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

layout: Support running the firmware as a BIOS image #24

Open
wants to merge 3 commits into
base: main
Choose a base branch
from
Open

layout: Support running the firmware as a BIOS image #24

wants to merge 3 commits into from

Commits on Sep 10, 2020

  1. gdt: Add definitions for 32-bit GDT 

    Our 32-bit GDT just has 1 code and 1 data segment descriptor. They are
both flat (spanning the entire 4G address space) and are placed in
normal static memory (for now).

Signed-off-by: Joe Richey <[email protected]>
    @josephlr
    josephlr committed Sep 10, 2020
    Configuration menu
    Copy the full SHA
    a91b400 View commit details
    Browse the repository at this point in the history

  2. bios: Add code to boot as Firmware ROM 

    The new assembly files handle:
  - reset.s: Jumping from reset
  - rom16.s: Transitioning to 32-bit mode
  - rom32.s: Copying data from ROM to RAM, jumping to PVH entry point

To place this code correctly, we add a new Program Header for the code
and data that expect to be in ROM. See the comments in layout.ld for
more information.

We also place the 32-bit GDT in the ROM. This is mostly for convenience,
as it lets us use the GDT directly from the ROM code without having to
do any complex offset calculations.

As laying out the code for a ROM makes the binary ~45% bigger, we gate
building as a ROM behind an optional feature.

Signed-off-by: Joe Richey <[email protected]>
    @josephlr
    josephlr committed Sep 10, 2020
    Configuration menu
    Copy the full SHA
    ae54aed View commit details
    Browse the repository at this point in the history

  3. bios: Make sure PVH still works with "rom" feature 

    Without this change, QEMU/CloudHV will attempt to load the ROM into the
memory region below 4GiB. But something (i.e. SeaBIOS) is already there.

We just pick an arbitrary address. It doesn't actually matter where it
gets loaded, as the ROM code isn't used when doing PVH boot.

Signed-off-by: Joe Richey <[email protected]>
    @josephlr
    josephlr committed Sep 10, 2020
    Configuration menu
    Copy the full SHA
    8961efc View commit details
    Browse the repository at this point in the history