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

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

We have some internal feature, required to run the code at the each SMI entrypoint, instead of common code.
That is why we write code in previous way.

I suggest we keep using the previous way and provide a good example on how to handle absolute address in new way.

Can we provide an update for below:
> >    mov   rax, ASM_PFX(CpuSmmDebugEntry)
> >    call    rax

Thank you
Yao Jiewen

> -----Original Message-----
> From: Gao, Liming
> Sent: Wednesday, September 12, 2018 9:30 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>; Gao, Liming <liming.gao@intel.com>
> Subject: RE: [edk2] [Patch] UefiCpuPkg PiSmmCpuDxeSmm: Remove
> unnecessary jmp _SmiHandler
> 
> Jiewen:
>   Because nasm doesn't generate the absolute address, we can change the
> below code, but we need to fix up its value at boot time like current
> _SmiHandler way.
> 
>   Could you let me know why can't use current way?
> 
> Thanks
> Liming
> >-----Original Message-----
> >From: Yao, Jiewen
> >Sent: Wednesday, September 12, 2018 9:04 AM
> >To: Gao, Liming <liming.gao@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
> >
> >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
> >> >> _______________________________________________
> >> >> edk2-devel mailing list
> >> >> edk2-devel@lists.01.org
> >> >> https://lists.01.org/mailman/listinfo/edk2-devel