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

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

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
> 
> 
> 
> 
>