Re: [PATCH] ArmPlatformPkg/PrePeiCore: seed temporary stack before entering PEI core

[Laszlo Ersek <lersek@redhat.com>]

On 10/20/17 15:00, Leif Lindholm wrote:
> On Fri, Oct 20, 2017 at 12:23:25PM +0100, Ard Biesheuvel wrote:
>> DEBUG builds of PEI code will print a diagnostic message regarding
>> the utilization of temporary RAM before switching to permanent RAM.
>> For example,
>>
>>   Total temporary memory:    16352 bytes.
>>     temporary memory stack ever used:       4820 bytes.
>>     temporary memory heap used for HobList: 4720 bytes.
>>
>> Tracking stack utilization like this requires the stack to be seeded
>> with a known magic value, and this needs to occur before entering C
>> code, given that it uses the stack. Currently, only Nt32Pkg appears
>> to implement this feature, but it is useful nonetheless, so let's
>> wire it up for PrePeiCore.
>>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>>  ArmPlatformPkg/PrePeiCore/AArch64/PrePeiCoreEntryPoint.S |  7 +++++++
>>  ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.S     | 10 ++++++++++
>>  ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.asm   | 10 ++++++++++
>>  3 files changed, 27 insertions(+)
>>
>> diff --git a/ArmPlatformPkg/PrePeiCore/AArch64/PrePeiCoreEntryPoint.S b/ArmPlatformPkg/PrePeiCore/AArch64/PrePeiCoreEntryPoint.S
>> index aab5edab0c42..7a33e2754869 100644
>> --- a/ArmPlatformPkg/PrePeiCore/AArch64/PrePeiCoreEntryPoint.S
>> +++ b/ArmPlatformPkg/PrePeiCore/AArch64/PrePeiCoreEntryPoint.S
>> @@ -13,6 +13,8 @@
>>  
>>  #include <AsmMacroIoLibV8.h>
>>  
>> +#define INIT_CAR_VALUE      0x5AA55AA55AA55AA5
>> +
>>  ASM_FUNC(_ModuleEntryPoint)
>>    // Do early platform specific actions
>>    bl    ASM_PFX(ArmPlatformPeiBootAction)
>> @@ -84,4 +86,9 @@ _PrepareArguments:
>>  
>>  _SetupPrimaryCoreStack:
>>    mov   sp, x1
>> +  MOV64 (x8, FixedPcdGet64(PcdCPUCoresStackBase))
>> +  MOV64 (x9, INIT_CAR_VALUE)
>> +0:stp   x9, x9, [x8], #16
>> +  cmp   x8, x1
>> +  b.lt  0b
>>    b     _PrepareArguments
>> diff --git a/ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.S b/ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.S
>> index 14344425ad4c..7342e49bea59 100644
>> --- a/ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.S
>> +++ b/ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.S
>> @@ -13,6 +13,8 @@
>>  
>>  #include <AsmMacroIoLib.h>
>>  
>> +#define INIT_CAR_VALUE      0x5AA55AA5
>> +
> 
> Worth moving to a common header somewhere?
> 
> Also defined/used in MdeModulePkg/Core/Pei/Dispatcher/Dispatcher.c.

Furthermore, open-coded in:

EmulatorPkg/Unix/Host/Host.c:    *StackPointer = 0x5AA55AA5;
Nt32Pkg/Sec/SecMain.c:    *StackPointer = 0x5AA55AA5;

Honestly I think it should be a Fixed-At-Build PCD, in MdeModulePkg.dec,
similarly to

  gEfiMdePkgTokenSpaceGuid.PcdDebugClearMemoryValue

in MdePkg.dec.

I'm unhappy that we have to annoy Ard with a request to "upstream" this
constant to MdeModulePkg in some form, but we'll need it yet again in
OVMF...

> 
> That file has an explicit comment saying "temporary memory is filled
> with this initial value during SEC phase". Should this end have a
> corresponding comment saying "checked for during PEI phase"?

Thanks
Laszlo

> 
> /
>     Leif
> 
>>  ASM_FUNC(_ModuleEntryPoint)
>>    // Do early platform specific actions
>>    bl    ASM_PFX(ArmPlatformPeiBootAction)
>> @@ -65,6 +67,14 @@ _PrepareArguments:
>>  
>>  _SetupPrimaryCoreStack:
>>    mov   sp, r1
>> +  MOV32 (r8, FixedPcdGet64(PcdCPUCoresStackBase))
>> +  MOV32 (r9, INIT_CAR_VALUE)
>> +  mov   r10, r9
>> +  mov   r11, r9
>> +  mov   r12, r9
>> +0:stm   r8!, {r9-r12}
>> +  cmp   r8, r1
>> +  blt   0b
>>    b     _PrepareArguments
>>  
>>  _NeverReturn:
>> diff --git a/ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.asm b/ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.asm
>> index abea675828df..7455de8aa66e 100644
>> --- a/ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.asm
>> +++ b/ArmPlatformPkg/PrePeiCore/Arm/PrePeiCoreEntryPoint.asm
>> @@ -13,6 +13,8 @@
>>  
>>  #include <AutoGen.h>
>>  
>> +#define INIT_CAR_VALUE      0x5AA55AA5
>> +
>>    INCLUDE AsmMacroIoLib.inc
>>  
>>    IMPORT  CEntryPoint
>> @@ -79,6 +81,14 @@ _PrepareArguments
>>  
>>  _SetupPrimaryCoreStack
>>    mov   sp, r1
>> +  mov32 r8, FixedPcdGet64(PcdCPUCoresStackBase)
>> +  mov32 r9, INIT_CAR_VALUE
>> +  mov   r10, r9
>> +  mov   r11, r9
>> +  mov   r12, r9
>> +0:stm   r8!, {r9-r12}
>> +  cmp   r8, r1
>> +  blt   0b
>>    b     _PrepareArguments
>>  
>>  _NeverReturn
>> -- 
>> 2.11.0
>>