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

["Guo Dong" <guo.dong@intel.com>]

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
> >
> >
> >
> > 
> >