From: "Brian J. Johnson" <brian.johnson@hpe.com>
To: <devel@edk2.groups.io>, <afish@apple.com>, <yoshinoyatoko@163.com>
Subject: Re: [edk2-devel] Access 64bit address space in 32bit mode
Date: Wed, 9 Nov 2022 14:40:49 -0600 [thread overview]
Message-ID: <92c4c7a9-90d0-ce98-6d50-8b1533802cd3@hpe.com> (raw)
In-Reply-To: <CC64DA9B-0378-44B0-8BA3-2237636B9891@apple.com>
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Slight correction: PAE paging can access up to 52 physical address
bits, for 4 PBytes of memory. Section 4.4 of the Intel® 64 and IA-32
Architectures Software Developer’s Manual Volume 3 (3A, 3B, 3C & 3D):
System Programming Guide covers it.
Brian J. Johnson
------------------------------------------------------------------------
*From:* Andrew Fish via groups.io [mailto:afish=apple.com@groups.io]
*Sent:* Wednesday, November 9, 2022 at 11:20 AM
*To:* devel@edk2.groups.io, yoshinoyatoko@163.com
*Subject:* [edk2-devel] Access 64bit address space in 32bit mode
>
>> On Nov 7, 2022, at 7:16 PM, Yoshinoya <yoshinoyatoko@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
> <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>
>
> <https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/X64/Thunk16.nasm>
> edk2.png
> 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>
>
> <https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/Ia32/Thunk16.nasm>
>
> Thanks,
>
> Andrew Fish
>
>
>> Thanks
>
>
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next prev parent reply other threads:[~2022-11-09 20:41 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-05 11:32 [edk2-devel] Python368.efi failed to run in shell environment Yoshinoya
2022-10-05 16:28 ` Michael D Kinney
2022-10-11 10:20 ` Yoshinoya
2022-10-18 9:04 ` Jayaprakash, N
2022-10-19 8:30 ` Yoshinoya
2022-10-19 13:16 ` Jayaprakash, N
2022-10-20 3:06 ` Yoshinoya
2022-10-20 3:18 ` Jayaprakash, N
2022-11-08 3:16 ` [edk2-devel] Access 64bit address space in 32bit mode Yoshinoya
2022-11-09 17:20 ` Andrew Fish
2022-11-09 18:58 ` vincent zimmer
2022-11-09 20:14 ` Andrew Fish
2023-02-18 0:55 ` [edk2-devel] PciBus scan: Does it support scan from EndBusNum to StartBusNum? Yoshinoya
2023-02-20 4:28 ` Yoshinoya
2023-02-21 1:27 ` Yoshinoya
2023-02-21 2:47 ` Yoshinoya
2023-02-21 19:18 ` Pedro Falcato
2023-02-22 1:10 ` Tiger Liu(BJ-RD)
2023-02-22 1:22 ` Pedro Falcato
2023-05-23 9:55 ` [edk2-devel] PciHostBridge: dynamic pcie bus limit assignment Yoshinoya
2022-11-09 20:40 ` Brian J. Johnson [this message]
2023-01-03 9:04 ` [edk2-devel] PciBus driver: support pcie 4.0 bus/device enumeration ? Yoshinoya
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