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

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 20 October 2017 at 16:43, Laszlo Ersek <lersek@redhat.com> wrote:
> 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.
>

Yes. And you both know how the MdeModulePkg maintainers are going to
respond if I propose adding another PCD.

> 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
>>>
>