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

["Gao, Liming" <liming.gao@intel.com>]

This is for debug purpose. I think UINT32 is OK if AARCH64 can operate 32bit value. 

Thanks
Liming
> -----Original Message-----
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Saturday, October 21, 2017 1:19 AM
> To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Gao, Liming <liming.gao@intel.com>; edk2-devel@lists.01.org; Leif Lindholm <leif.lindholm@linaro.org>
> Subject: Re: [edk2] [PATCH] ArmPlatformPkg/PrePeiCore: seed temporary stack before entering PEI core
> 
> On 10/20/17 18:52, Ard Biesheuvel wrote:
> > On 20 October 2017 at 17:51, Laszlo Ersek <lersek@redhat.com> wrote:
> >> On 10/20/17 18:39, Ard Biesheuvel wrote:
> >>> On 20 October 2017 at 17:37, Gao, Liming <liming.gao@intel.com> wrote:
> >>>> Ard:
> >>>>   This case is to share the same value between PeiCore and SecCore. I also think it will be better to define one fixed PCD in
> MdeModulePkg.dec for this value. Could you submit bugzillar to catch this issue first?
> >>>>
> >>>
> >>> Certainly!
> >>
> >> Would it be possible to define the PCD as UINT32, and task 64-bit SEC
> >> (and PEI_CORE) code to first construct the wider value manually (in a
> >> register or otherwise)?
> >>
> >> Just thinking out loud.
> >>
> >
> > Could you think the reasoning behind that out loud as well?
> 
> Haha, good stab :) Sure.
> 
> In your patch you have:
> 
> +#define INIT_CAR_VALUE      0x5AA55AA55AA55AA5
> 
> for 64-bit, and
> 
> +#define INIT_CAR_VALUE      0x5AA55AA5
> 
> for 32-bit.
> 
> Both 64-bit assembly code in SEC, and 64-bit C-code in the PEI_CORE, can
> easily compose the large value from the small value, starting from
> FixedPcdGet32(). The alternatives are:
> 
> - asking the 32-bit assembly code to truncate the 64-bit constant -- it
> won't compile,
> 
> - defining *two* FixedAtBuild PCDs, one for 32-bit, another for 64-bit
> SEC -- an idea probably not universally liked.
> 
> ... When I originally started writing my previous email, I even thought
> about introducing the PCD as UINT16 :) But then I realized, if any
> platform lacks *some* 32-bit mode when it sets up the stack in assembly,
> for C-language entry, then the platform won't be supported by edk2.
> 
> Thanks
> Laszlo