Re: UefiCpuPkg/CpuDxe: Fix boot error

["Michael D Kinney" <michael.d.kinney@intel.com>]

Guo,

Yes.  Using the following looks like the correct solution:

	o64 retf

Thanks,

Mike

> -----Original Message-----
> From: Dong, Guo <guo.dong@intel.com>
> Sent: Wednesday, January 6, 2021 2:07 PM
> To: devel@edk2.groups.io; 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: FW: UefiCpuPkg/CpuDxe: Fix boot error
> 
> 
> Hi Mike,
> 
> I just did a test with retfq, it looks the compiler will take 'retfq' as a label with a warnig:
> "CpuAsm.iii:26: warning: label alone on a line without a colon might be in error"
> 
> CpuAsm.nasm is the source file.
> Both CpuAsm.iii and CpuAsm.obj are from the build folder.
> CpuAsm_dasm.txt is the dasm file using objdump.
> 
> I am using "NASM version 2.12.01rc2 compiled on Mar  7 2016".
> BTW, if using "O64 retf" instead of "retfq", the generated obj matches with DB one.
> Do you prefer using " O64 retf" comparing with "DB 0x48, 0xcb"?
> 
> Thanks,
> Guo
> 
> > -----Original Message-----
> > From: Kinney, Michael D <michael.d.kinney@intel.com>
> > Sent: Tuesday, January 5, 2021 7:01 PM
> > To: Dong, Guo <guo.dong@intel.com>; devel@edk2.groups.io; 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,
> >
> > Could be the port from MASM to NASM did not check to see if NASM supported
> > the instruction.
> >
> > You can verify the NASM disassembly to make sure it matches the DB bytes.
> >
> > 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
> > > > >
> > > > >
> > > > >
> > > > > 
> > > > >