f04e76bcf0
Describe state and assuptions made about x86_64 support. Change-Id: I308a09b0eac269afd30df95ed3ea195238a6cfbe Signed-off-by: Patrick Rudolph <siro@das-labor.org> Reviewed-on: https://review.coreboot.org/c/30056 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Patrick Georgi <pgeorgi@google.com>
43 lines
1.6 KiB
Markdown
43 lines
1.6 KiB
Markdown
# x86 architecture documentation
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This section contains documentation about coreboot on x86 architecture.
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## State of x86_64 support
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At the moment there's no single board that supports x86_64 or to be exact
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`ARCH_RAMSTAGE_X86_64` and `ARCH_ROMSTAGE_X86_64`.
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In order to add support for x86_64 the following assumptions are made:
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* The CPU supports long mode
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* All memory returned by malloc must be below 4GiB in physical memory
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* All code that is to be run must be below 4GiB in physical memory
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* The high dword of pointers is always zero
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* The reference implementation is qemu
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* The CPU supports 1GiB hugepages
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## Assuptions for ARCH_ROMSTAGE_X86_64 reference implementation
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* 0-4GiB are identity mapped using 1GiB huge-pages
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* Memory above 4GiB isn't accessible
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* pagetables reside in _pagetables
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* Romstage must install new pagetables in CBMEM after RAMINIT
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## Assuptions for ARCH_RAMSTAGE_X86_64 reference implementation
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* Romstage installed pagetables according to memory layout
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* Memory above 4GiB is accessible
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## Steps to add basic support for x86_64
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* Add x86_64 toolchain support - *DONE*
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* Fix compilation errors - *DONE*
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* Fix linker errors - *TODO*
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* Add x86_64 rmodule support - *ONGERRIT*
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* Add x86_64 exception handlers - *TODO*
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* Setup page tables for long mode - *TODO*
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* Add assembly code for long mode - *TODO*
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* Add assembly code to return to protected mode - *TODO*
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* Implement reference code for mainboard `emulation/qemu-q35` - *TODO*
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## Porting other boards
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* Fix compilation errors
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* Test how well CAR works with x86_64 and paging
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* Improve mode switches
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* Test libgfxinit / VGA Option ROMs / FSP
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