Re: [edk2-devel] [PATCH] UefiCpuPkg/CpuDxe: Fix boot error

["Laszlo Ersek" <lersek@redhat.com>]

On 01/06/21 03:00, Kinney, Michael D wrote:
> Hi Guo,
> 
> Could be the port from MASM to NASM did not check to see if NASM supported the instruction.

I agree: ad8ae98d2fa2 ("OvmfPkg LoadLinuxLib: Convert
X64/JumpToKernel.asm to NASM", 2014-10-31). I seem to remember that
Jordan implemented that large MASM->NASM conversion series mostly
mechanically (which was the right approach, of course, given the number
of assembly files, and the regression risks).

> You can verify the NASM disassembly to make sure it matches the DB bytes.

Thanks!
Laszlo

> 
> Mike
> 
>> -----Original Message-----
>> From: Dong, Guo <guo.dong@intel.com>
>> Sent: Tuesday, January 5, 2021 4:51 PM
>> To: Kinney, Michael D <michael.d.kinney@intel.com>; devel@edk2.groups.io
>> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; lersek@redhat.com; Kumar, Rahul1
>> <rahul1.kumar@intel.com>
>> Subject: RE: [edk2-devel] [PATCH] UefiCpuPkg/CpuDxe: Fix boot error
>>
>>
>> Hi Mike,
>>
>> Thanks for the comments. I will remove DB and submit a new patch.
>> I used DB because retfq is used in EDK2 only in OvmfPkg\Library\LoadLinuxLib\X64\JumpToKernel.nasm and it used DB.
>> Not sure if there is any BKM why they use it.
>>
>> Thanks,
>> Guo
>>
>>> -----Original Message-----
>>> From: Kinney, Michael D <michael.d.kinney@intel.com>
>>> Sent: Monday, January 4, 2021 9:31 PM
>>> To: devel@edk2.groups.io; Dong, Guo <guo.dong@intel.com>; Kinney, Michael
>>> D <michael.d.kinney@intel.com>
>>> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>;
>>> lersek@redhat.com; Kumar, Rahul1 <rahul1.kumar@intel.com>
>>> Subject: RE: [edk2-devel] [PATCH] UefiCpuPkg/CpuDxe: Fix boot error
>>>
>>> Hi Guo,
>>>
>>> NASM has good support for instructions.  Can the DB be removed and replaced
>>> with the equivalent instruction?
>>>
>>> Thanks,
>>>
>>> Mike
>>>
>>>> -----Original Message-----
>>>> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Guo Dong
>>>> Sent: Thursday, December 24, 2020 12:04 PM
>>>> To: devel@edk2.groups.io
>>>> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>;
>>> lersek@redhat.com; Kumar, Rahul1
>>>> <rahul1.kumar@intel.com>
>>>> Subject: [edk2-devel] [PATCH] UefiCpuPkg/CpuDxe: Fix boot error
>>>>
>>>> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3084
>>>>
>>>> When DXE drivers are dispatched above 4GB memory in 64bit
>>>> mode, the address setCodeSelectorLongJump in stack will
>>>> be override by parameter. Jump to Qword is not supported
>>>> by some processors. So use retfq instead.
>>>>
>>>> Signed-off-by: Guo Dong <guo.dong@intel.com>
>>>> ---
>>>>  UefiCpuPkg/CpuDxe/X64/CpuAsm.nasm | 8 +++-----
>>>>  1 file changed, 3 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/UefiCpuPkg/CpuDxe/X64/CpuAsm.nasm
>>> b/UefiCpuPkg/CpuDxe/X64/CpuAsm.nasm
>>>> index c3489bcc3e..e33ddb2784 100644
>>>> --- a/UefiCpuPkg/CpuDxe/X64/CpuAsm.nasm
>>>> +++ b/UefiCpuPkg/CpuDxe/X64/CpuAsm.nasm
>>>> @@ -20,13 +20,11 @@
>>>>  ;------------------------------------------------------------------------------
>>>>  global ASM_PFX(SetCodeSelector)
>>>>  ASM_PFX(SetCodeSelector):
>>>> -    sub     rsp, 0x10
>>>> +    push    rcx,
>>>>      lea     rax, [setCodeSelectorLongJump]
>>>> -    mov     [rsp], rax
>>>> -    mov     [rsp+4], cx
>>>> -    jmp     dword far [rsp]
>>>> +    push    rax
>>>> +    DB 0x48, 0xcb                      ; retfq
>>>>  setCodeSelectorLongJump:
>>>> -    add     rsp, 0x10
>>>>      ret
>>>>
>>>>  ;------------------------------------------------------------------------------
>>>> --
>>>> 2.16.2.windows.1
>>>>
>>>>
>>>>
>>>> 
>>>>
>