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