Re: [edk2-devel] [PATCH 02/10] OvmfPkg/ResetVector: add ClearOvmfPageTables macro

["Gerd Hoffmann" <kraxel@redhat.com>]

On Wed, Feb 28, 2024 at 05:09:32AM +0100, Laszlo Ersek wrote:
> On 2/22/24 12:54, Gerd Hoffmann wrote:
> > Move code to clear the page tables to a nasm macro.
> > No functional change.
> > 
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > ---
> >  OvmfPkg/ResetVector/Ia32/PageTables64.asm | 35 ++++++++++++-----------
> >  1 file changed, 19 insertions(+), 16 deletions(-)
> > 
> > diff --git a/OvmfPkg/ResetVector/Ia32/PageTables64.asm b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> > index 6fec6f2beeea..378ba2feeb4f 100644
> > --- a/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> > +++ b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
> > @@ -45,6 +45,24 @@ BITS    32
> >  %define TDX_BSP         1
> >  %define TDX_AP          2
> >  
> > +;
> > +; For OVMF, build some initial page tables at
> > +; PcdOvmfSecPageTablesBase - (PcdOvmfSecPageTablesBase + 0x6000).
> > +;
> > +; This range should match with PcdOvmfSecPageTablesSize which is
> > +; declared in the FDF files.
> > +;
> > +; At the end of PEI, the pages tables will be rebuilt into a
> > +; more permanent location by DxeIpl.
> > +;
> > +%macro ClearOvmfPageTables 0
> > +    mov     ecx, 6 * 0x1000 / 4
> > +    xor     eax, eax
> > +.clearPageTablesMemoryLoop:
> > +    mov     dword[ecx * 4 + PT_ADDR (0) - 4], eax
> > +    loop    .clearPageTablesMemoryLoop
> > +%endmacro
> > +
> >  ;
> >  ; Modified:  EAX, EBX, ECX, EDX
> >  ;
> 
> Ah, this made me read up on local labels:
> 
> https://www.nasm.us/xdoc/2.16.01/html/nasmdoc3.html#section-3.9
> 
> Should we rather call the label
> 
>   ..@clearPageTablesMemoryLoop
> 
> ?

I've tried that and something (which I don't remember) didn't work as
expected.  Given that each branch which uses that macro will have a jump
label anyway (so the local label is expanded to something like
TdxBspInit.clearPageTablesMemoryLoop) I've figured this is good enough

take care,
  Gerd



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