Re: [Patch] UefiCpuPkg PiSmmCpuDxeSmm: Remove unnecessary jmp _SmiHandler

["Yao, Jiewen" <jiewen.yao@intel.com>]

The original code is below. Can we rollback to the indirect call?

    mov   rax, ASM_PFX(CpuSmmDebugEntry)
    call    rax

Thank you
Yao Jiewen

> -----Original Message-----
> From: Gao, Liming
> Sent: Wednesday, September 12, 2018 8:59 AM
> To: Yao, Jiewen <jiewen.yao@intel.com>; Laszlo Ersek <lersek@redhat.com>;
> edk2-devel@lists.01.org
> Cc: Dong, Eric <eric.dong@intel.com>
> Subject: RE: [edk2] [Patch] UefiCpuPkg PiSmmCpuDxeSmm: Remove
> unnecessary jmp _SmiHandler
> 
> Jiewen:
>   After do more verification, I recall this change. Current code is really
> required. Without it, OVMF SMM can't boot. So, below code can't be
> removed.
>   The reason is that nasm _SmiEntryPoint() function is copied to another
> memory location and run. But, _ SmiEntryPoint() calls the external C function
> CpuSmmDebugEntry(). nasm compiler generates the function call with the
> relative address. After _SmiEntryPoint() function is copied and run in the new
> address, its external function call will not work. To fix it, I add jmp instruction
> to the original address, then process function all and works.
> 
>     mov     rax, strict qword 0         ;   mov     rax, _SmiHandler
> _SmiHandlerAbsAddr:
>     jmp     rax
> 
> ...
>     mov     rcx, rbx
>     call    ASM_PFX(CpuSmmDebugEntry)
> 
> Thanks
> Liming
> >-----Original Message-----
> >From: Yao, Jiewen
> >Sent: Wednesday, September 12, 2018 6:03 AM
> >To: Laszlo Ersek <lersek@redhat.com>; Gao, Liming
> <liming.gao@intel.com>;
> >edk2-devel@lists.01.org
> >Cc: Dong, Eric <eric.dong@intel.com>
> >Subject: RE: [edk2] [Patch] UefiCpuPkg PiSmmCpuDxeSmm: Remove
> >unnecessary jmp _SmiHandler
> >
> >HI
> >Would you please add info on what unit test has been done?
> >
> >Thank you
> >Yao Jiewen
> >
> >
> >> -----Original Message-----
> >> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> >> Laszlo Ersek
> >> Sent: Tuesday, September 11, 2018 11:06 PM
> >> To: Gao, Liming <liming.gao@intel.com>; edk2-devel@lists.01.org
> >> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Dong, Eric
> <eric.dong@intel.com>
> >> Subject: Re: [edk2] [Patch] UefiCpuPkg PiSmmCpuDxeSmm: Remove
> >> unnecessary jmp _SmiHandler
> >>
> >> On 09/10/18 10:20, Liming Gao wrote:
> >> > This change is wrong introduced by
> >> e21e355e2ca7fefb15b4df7078f995d3fb9c2b89
> >> > It is not required. So, revert it.
> >> >
> >> > Contributed-under: TianoCore Contribution Agreement 1.1
> >> > Signed-off-by: Liming Gao <liming.gao@intel.com>
> >> > Cc: Jiewen Yao <jiewen.yao@intel.com>
> >> > ---
> >> >  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmiEntry.nasm | 9 ++-------
> >> >  1 file changed, 2 insertions(+), 7 deletions(-)
> >> >
> >> > diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmiEntry.nasm
> >> b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmiEntry.nasm
> >> > index 315d0f8..7b1b3ca 100644
> >> > --- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmiEntry.nasm
> >> > +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmiEntry.nasm
> >> > @@ -173,9 +173,8 @@ SmiHandlerIdtrAbsAddr:
> >> >      mov     gs, eax
> >> >      mov     ax, [rbx + DSC_SS]
> >> >      mov     ss, eax
> >> > -    mov     rax, strict qword 0         ;   mov     rax,
> >> _SmiHandler
> >> > -_SmiHandlerAbsAddr:
> >> > -    jmp     rax
> >> > +
> >> > +;   jmp     _SmiHandler                 ; instruction is not
> needed
> >> >
> >> >  _SmiHandler:
> >> >      mov     rbx, [rsp + 0x8]             ; rcx <- CpuIndex
> >> > @@ -229,8 +228,4 @@ ASM_PFX(PiSmmCpuSmiEntryFixupAddress):
> >> >      lea    rax, [ASM_PFX(gSmiHandlerIdtr)]
> >> >      lea    rcx, [SmiHandlerIdtrAbsAddr]
> >> >      mov    qword [rcx - 8], rax
> >> > -
> >> > -    lea    rax, [_SmiHandler]
> >> > -    lea    rcx, [_SmiHandlerAbsAddr]
> >> > -    mov    qword [rcx - 8], rax
> >> >      ret
> >> >
> >>
> >> Please remember to CC package maintainers / reviewers directly.
> >>
> >> The patch makes sense to me, and indeed it restores the original code.
> >>
> >> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> >>
> >> Can you perhaps add another sentence to the commit message, before
> you
> >> push the patch, such as "the original code already uses RIP-relative
> >> addressing"?
> >>
> >> Thanks
> >> Laszlo
> >> _______________________________________________
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