We used GRUB to modeset the resolution for a long time, but for good
reasons I see no point with keeping it supported in our kernel. We
support bochs-display device on QEMU (both the VGA compatible and
non-VGA compatible variants), so for QEMU we can still boot the system
in graphical mode even without GRUB help.
Also, we now have a native driver for Intel graphics and although it
doesn't support most Intel graphics cards out there yet, it's a good
starting point to support more cards. If a user wants to boot on
bare-metal in graphical mode, all he needs to do is to add the removed
flag back again, as the kernel still supports pre-set framebuffers.
We were only 448 KiB away from filling up the old slot size we reserve
for the kernel above the 3 GiB mark. This expands the slot to 16 MiB,
which allows us to continue booting the kernel until somebody takes
the time to improve our loader.
When building the kernel with -O2, we somehow ended up with the kernel
command line outside of the lower 8MB of physical memory. Since we don't
map that area in our initial page table setup, we would triple fault
when trying to parse the command line.
This patch sidesteps the issue by copying the (first 4KB of) the kernel
command line to a buffer in a known safe location at boot.
Both ESP and GDTR are left undefined by the Multiboot specification and
OS images must not rely on these values to be valid. Fix the undefined
behaviors so that booting with PXELINUX does not triple-fault the CPU.
The kernel and its static data structures are no longer identity-mapped
in the bottom 8MB of the address space, but instead move above 3GB.
The first 8MB above 3GB are pseudo-identity-mapped to the bottom 8MB of
the physical address space. But things don't have to stay this way!
Thanks to Jesse who made an earlier attempt at this, it was really easy
to get device drivers working once the page tables were in place! :^)
Fixes#734.
Introduce one more (CPU) indirection layer in the paging code: the page
directory pointer table (PDPT). Each PageDirectory now has 4 separate
PageDirectoryEntry arrays, governing 1 GB of VM each.
A really neat side-effect of this is that we can now share the physical
page containing the >=3GB kernel-only address space metadata between
all processes, instead of lazily cloning it on page faults.
This will give us access to the NX (No eXecute) bit, allowing us to
prevent execution of memory that's not supposed to be executed.
The kernel is now no longer identity mapped to the bottom 8MiB of
memory, and is now mapped at the higher address of `0xc0000000`.
The lower ~1MiB of memory (from GRUB's mmap), however is still
identity mapped to provide an easy way for the kernel to get
physical pages for things such as DMA etc. These could later be
mapped to the higher address too, as I'm not too sure how to
go about doing this elegantly without a lot of address subtractions.
