Re: [edk2-devel] [Patch V2] UefiCpuPkg/CpuExceptionHandlerLib: Code optimization to allow bigger stack

["Chang, Abner" <abner.chang@amd.com>]

[AMD Official Use Only - General]

Not the maintainer or reviewer, however Reviewed-by: Abner Chang <abner.chang@amd.com>

> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of duntan via
> groups.io
> Sent: Thursday, September 29, 2022 5:07 PM
> 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 V2] 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>
> Reviewed-by: Ray Ni <ray.ni@intel.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> ---
>  UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c | 5
> ++++-
> UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c  | 5
> ++++-
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
> index 8c398ebc5b..c30ece1dc9 100644
> --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
> +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandle
> +++ r.c
> @@ -215,7 +215,10 @@ ArchSetupExceptionStack (
>    // Fixup exception task descriptor and task-state segment
>    //
>    AsmGetTssTemplateMap (&TemplateMap);
> -  StackTop = StackTop - CPU_STACK_ALIGNMENT;
> +  //
> +  // Plus 1 byte is for compact stack layout in case StackTop is already aligned.
> +  //
> +  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)
> { diff --git
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> index 80e9f08e5b..4e85880ed4 100644
> --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler
> +++ .c
> @@ -223,7 +223,10 @@ ArchSetupExceptionStack (
>    // Fixup exception task descriptor and task-state segment
>    //
>    ZeroMem (Tss, sizeof (*Tss));
> -  StackTop = StackTop - CPU_STACK_ALIGNMENT;
> +  //
> +  // Plus 1 byte is for compact stack layout in case StackTop is already aligned.
> +  //
> +  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
> 
> 
> 
> 
>