Re: [edk2-devel] [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: Code optimization to allow bigger stack

["duntan" <dun.tan@intel.com>]

Hi Abner,

Thanks for the comments. I'll add comments on this code change to explain it in V2 patch.

Thanks,
Dun
-----Original Message-----
From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Chang, Abner via groups.io
Sent: Thursday, September 29, 2022 9:05 AM
To: devel@edk2.groups.io; Tan, Dun <dun.tan@intel.com>
Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Kumar, Rahul R <rahul.r.kumar@intel.com>
Subject: Re: [edk2-devel] [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: Code optimization to allow bigger stack

[AMD Official Use Only - General]



> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of duntan 
> via groups.io
> Sent: Wednesday, September 28, 2022 9:52 AM
> To: devel@edk2.groups.io
> Cc: Eric Dong <eric.dong@intel.com>; Ray Ni <ray.ni@intel.com>; Rahul 
> Kumar <rahul1.kumar@intel.com>
> Subject: [edk2-devel] [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: Code 
> optimization to allow bigger stack
> 
> Caution: This message originated from an External Source. Use proper 
> caution when opening attachments, clicking links, or responding.
> 
> 
> This commit is a code optimization to allow bigger seperate stack size 
> in ArchSetupExceptionStack. In previous code logic, 
> CPU_STACK_ALIGNMENT bytes will be wasted if StackTop is already CPU_STACK_ALIGNMENT aligned.
> 
> Signed-off-by: Dun Tan <dun.tan@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> ---
>  UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c 
> |
> 2 +-
> UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c  
> |
> 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.
> c 
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.
> c
> index 8c398ebc5b..c8fa30a32f 100644
> ---
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.
> c
> +++
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandle
> +++ r.c
> @@ -215,7 +215,7 @@ ArchSetupExceptionStack (
>    // Fixup exception task descriptor and task-state segment
>    //
>    AsmGetTssTemplateMap (&TemplateMap);
> -  StackTop = StackTop - CPU_STACK_ALIGNMENT;
> +  StackTop = StackTop - CPU_STACK_ALIGNMENT + 1;
Hi Dun,
Could you please add a comment on this change says the change is for the compact stack layout?
Thanks
Abner

>    StackTop = (UINTN)ALIGN_POINTER (StackTop, CPU_STACK_ALIGNMENT);
>    IdtTable = (IA32_IDT_GATE_DESCRIPTOR  *)Idtr.Base;
>    for (Index = 0; Index < CPU_STACK_SWITCH_EXCEPTION_NUMBER;
> ++Index) { diff --git
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> index 80e9f08e5b..74b2193cb0 100644
> ---
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> +++
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler
> +++ .c
> @@ -223,7 +223,7 @@ ArchSetupExceptionStack (
>    // Fixup exception task descriptor and task-state segment
>    //
>    ZeroMem (Tss, sizeof (*Tss));
> -  StackTop = StackTop - CPU_STACK_ALIGNMENT;
> +  StackTop = StackTop - CPU_STACK_ALIGNMENT + 1;
>    StackTop = (UINTN)ALIGN_POINTER (StackTop, CPU_STACK_ALIGNMENT);
>    IdtTable = (IA32_IDT_GATE_DESCRIPTOR  *)Idtr.Base;
>    for (Index = 0; Index < CPU_STACK_SWITCH_EXCEPTION_NUMBER;
> ++Index) {
> --
> 2.31.1.windows.1
> 
> 
> 
> 
>