Vincent, Thanks! I’d forgotten about that path.
The other answer is defer the work to a DXE driver that runs 64-bit x86. Thanks, Andrew Fish > On Nov 9, 2022, at 10:58 AM, vincent zimmer <vincent.zim...@gmail.com> wrote: > > we have the challenge of 32-bit PEI needing to access 64-bit addresses to > support 64-bit DXE/UEFI OS's in the capsule use-case scenario. This is > described in > https://raw.githubusercontent.com/tianocore-docs/Docs/master/White_Papers/A_Tour_Beyond_BIOS_Capsule_Update_and_Recovery_in_EDK_II.pdf > page 22 with code > https://github.com/tianocore/edk2/tree/master/MdeModulePkg/Universal/CapsulePei > > On Wed, Nov 9, 2022 at 9:21 AM Andrew Fish via groups.io <http://groups.io/> > <afish=apple....@groups.io <mailto:apple....@groups.io>> wrote: >> >>> On Nov 7, 2022, at 7:16 PM, Yoshinoya <yoshinoyat...@163.com >>> <mailto:yoshinoyat...@163.com>> wrote: >>> >>> Hello >>> Is it possible to access 64bit address space in 32bit mode? >>> >> >> I assume you are talking about x86? >> >> >>> For example, opcode prefix 0x66/67 could let code running in 16bit mode to >>> access 32bit data/address. >>> >> >> This is more complex than just instruction prefix. You need the CPU to be >> setup in big real mode via the GDT, so you basically have a 32-bit >> environment setup via GDT etc. Also the prefix opcodes have different >> meaning in different modes. I don’t think there is a way to make 32-bit code >> access 64-bit data via instruction prefix even if a 64-bit GDT was setup >> with paging enabled. >> >>> Or, establishing page table is a must requirement for accessing 64bit >>> address space. >>> >> >> For x86 you have to have 64-bit versions of the IDT, GDT, and you need to >> enable paging to enter 64-bit Long Mode. >> >> In a 32-bit x86 world you can access up to 64 GB of physical memory via >> using 32-bit page table using PAE [1]. PAE is a 32-bit virtual address >> space, but with support for a 36-bit physical address. I think in the olden >> days of 32-bit x86 EFI servers would have custom EFI code that enabled >> paging in 32-bit and carved out a chunk of the 32-bit memory space that >> could be mapped to 36-bit physical addresses. I think this was platform >> specific code and I don’t know of any open source version. The 32-bit Long >> Mode EFI does not have paging enabled, so adding PAE means enabling paging >> yourself. >> >> The edk2 has the opposite version of this code so you can call 16-bit really >> mode (Legacy BIOS) from 32-bit Protected mode, or 64-bit Long Mode. This is >> the code to Thunk for 32-bit/64-bit mode to 16-bit code [2]/ >> >> [1] https://en.wikipedia.org/wiki/Physical_Address_Extensio >> <https://en.wikipedia.org/wiki/Physical_Address_Extension>n >> <https://en.wikipedia.org/wiki/Physical_Address_Extension> >> [2] >> https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/X86Thunk.c >> <edk2.png> >> edk2/Thunk16.nasm at master · tianocore/edk2 >> github.com >> >> <https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/X64/Thunk16.nasm>edk2/Thunk16.nasm >> at master · tianocore/edk2 >> <https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/X64/Thunk16.nasm> >> github.com >> <https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/X64/Thunk16.nasm> >> >> edk2/Thunk16.nasm at master · tianocore/edk2 >> github.com >> >> <https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/Ia32/Thunk16.nasm>edk2/Thunk16.nasm >> at master · tianocore/edk2 >> <https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/Ia32/Thunk16.nasm> >> github.com >> <https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/Ia32/Thunk16.nasm> >> >> Thanks, >> >> Andrew Fish >> >> >>> Thanks >>> >> >> >> > > > <edk2.png> -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#96170): https://edk2.groups.io/g/devel/message/96170 Mute This Topic: https://groups.io/mt/94885261/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
