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

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

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
> > >
> > >
> > >
> > > 
> > >