Re: [PATCH 1/3] UefiCpuPkg/PiSmmCpuDxeSmm: update comments in IA32 SmmStartup()

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

Laszlo,

We have already used this technique in other NASM files
to remove DBs.

Let us know if you have suggestions on how to make the
C code that performs the patches easier to read and 
maintain.

Mike

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org]
> On Behalf Of Laszlo Ersek
> Sent: Tuesday, January 30, 2018 10:17 AM
> To: Kinney, Michael D <michael.d.kinney@intel.com>; edk2-
> devel-01 <edk2-devel@lists.01.org>
> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Paolo Bonzini
> <pbonzini@redhat.com>; Yao, Jiewen
> <jiewen.yao@intel.com>; Dong, Eric <eric.dong@intel.com>
> Subject: Re: [edk2] [PATCH 1/3]
> UefiCpuPkg/PiSmmCpuDxeSmm: update comments in IA32
> SmmStartup()
> 
> On 01/30/18 18:22, Kinney, Michael D wrote:
> > Laszlo,
> >
> > The DBs can be removed if the label is moved after
> > the instruction and the patch is done to the label
> > minus the size of the patch value.
> 
> Indeed I haven't thought of this.
> 
> If I understand correctly, it means
> 
>   extern UINT8 gSmmCr0;
> 
>   *(UINT32*)(&gSmmCr0 - sizeof (UINT32)) =
> (UINT32)AsmReadCr0 ();
> 
> TBH, the DB feels less ugly to me than this :)
> 
> Still, if you think it would be an acceptable price to
> pay for removing
> the remaining DBs, I can respin.
> 
> Thanks
> Laszlo
> 
> >> -----Original Message-----
> >> From: edk2-devel [mailto:edk2-devel-
> bounces@lists.01.org]
> >> On Behalf Of Laszlo Ersek
> >> Sent: Tuesday, January 30, 2018 7:34 AM
> >> To: edk2-devel-01 <edk2-devel@lists.01.org>
> >> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Yao, Jiewen
> >> <jiewen.yao@intel.com>; Dong, Eric
> <eric.dong@intel.com>;
> >> Paolo Bonzini <pbonzini@redhat.com>
> >> Subject: [edk2] [PATCH 1/3] UefiCpuPkg/PiSmmCpuDxeSmm:
> >> update comments in IA32 SmmStartup()
> >>
> >> The gSmmCr3, gSmmCr4, gSmmCr0 and gSmmJmpAddr global
> >> variables  are used
> >> for patching assembly instructions, thus we can never
> >> remove the DB
> >> encodings for those instructions. At least we should
> add
> >> the intended
> >> meanings in comments.
> >>
> >> This patch only changes comments.
> >>
> >> Cc: Eric Dong <eric.dong@intel.com>
> >> Cc: Jian J Wang <jian.j.wang@intel.com>
> >> Cc: Jiewen Yao <jiewen.yao@intel.com>
> >> Cc: Paolo Bonzini <pbonzini@redhat.com>
> >> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> >> Contributed-under: TianoCore Contribution Agreement
> 1.1
> >> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> >> ---
> >>  UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm | 8 ++++-
> ---
> >>  1 file changed, 4 insertions(+), 4 deletions(-)
> >>
> >> diff --git
> a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm
> >> b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm
> >> index e96dd8d2392a..08534dba64b7 100644
> >> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm
> >> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/SmmInit.nasm
> >> @@ -44,34 +44,34 @@ global ASM_PFX(SmmStartup)
> >>  ASM_PFX(SmmStartup):
> >>      DB      0x66
> >>      mov     eax, 0x80000001             ; read
> >> capability
> >>      cpuid
> >>      DB      0x66
> >>      mov     ebx, edx                    ; rdmsr will
> >> change edx. keep it in ebx.
> >> -    DB      0x66, 0xb8
> >> +    DB      0x66, 0xb8                  ; mov eax,
> imm32
> >>  ASM_PFX(gSmmCr3): DD 0
> >>      mov     cr3, eax
> >>      DB      0x67, 0x66
> >>      lgdt    [cs:ebp + (ASM_PFX(gcSmiInitGdtr) -
> >> ASM_PFX(SmmStartup))]
> >> -    DB      0x66, 0xb8
> >> +    DB      0x66, 0xb8                  ; mov eax,
> imm32
> >>  ASM_PFX(gSmmCr4): DD 0
> >>      mov     cr4, eax
> >>      DB      0x66
> >>      mov     ecx, 0xc0000080             ; IA32_EFER
> MSR
> >>      rdmsr
> >>      DB      0x66
> >>      test    ebx, BIT20                  ; check NXE
> >> capability
> >>      jz      .1
> >>      or      ah, BIT3                    ; set NXE bit
> >>      wrmsr
> >>  .1:
> >> -    DB      0x66, 0xb8
> >> +    DB      0x66, 0xb8                  ; mov eax,
> imm32
> >>  ASM_PFX(gSmmCr0): DD 0
> >>      DB      0xbf, PROTECT_MODE_DS, 0    ; mov di,
> >> PROTECT_MODE_DS
> >>      mov     cr0, eax
> >> -    DB      0x66, 0xea                   ; jmp far
> >> [ptr48]
> >> +    DB      0x66, 0xea                  ; jmp far
> >> [ptr48]
> >>  ASM_PFX(gSmmJmpAddr):
> >>      DD      @32bit
> >>      DW      PROTECT_MODE_CS
> >>  @32bit:
> >>      mov     ds, edi
> >>      mov     es, edi
> >> --
> >> 2.14.1.3.gb7cf6e02401b
> >>
> >>
> >> _______________________________________________
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> >> edk2-devel@lists.01.org
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> 
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