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x86 architecture documentation

This section contains documentation about coreboot on x86 architecture.

State of x86_64 support

At the moment there's no single board that supports x86_64 or to be exact ARCH_RAMSTAGE_X86_64 and ARCH_ROMSTAGE_X86_64.

In order to add support for x86_64 the following assumptions are made:

The CPU supports long mode
All memory returned by malloc must be below 4GiB in physical memory
All code that is to be run must be below 4GiB in physical memory
The high dword of pointers is always zero
The reference implementation is qemu
The CPU supports 1GiB hugepages

Assuptions for ARCH_ROMSTAGE_X86_64 reference implementation

0-4GiB are identity mapped using 1GiB huge-pages
Memory above 4GiB isn't accessible
pagetables reside in _pagetables
Romstage must install new pagetables in CBMEM after RAMINIT

Assuptions for ARCH_RAMSTAGE_X86_64 reference implementation

Romstage installed pagetables according to memory layout
Memory above 4GiB is accessible

Steps to add basic support for x86_64

Add x86_64 toolchain support - DONE
Fix compilation errors - DONE
Fix linker errors - TODO
Add x86_64 rmodule support - ONGERRIT
Add x86_64 exception handlers - TODO
Setup page tables for long mode - TODO
Add assembly code for long mode - TODO
Add assembly code to return to protected mode - TODO
Implement reference code for mainboard emulation/qemu-q35 - TODO

Porting other boards

Fix compilation errors
Test how well CAR works with x86_64 and paging
Improve mode switches
Test libgfxinit / VGA Option ROMs / FSP