So I figured this out and it was a microcode issue. I extracted another set of microcode mcbs for the target platform and added them to the FV, execution returned from TempInitRamApi. I was stuck on this since I didn't have any access to the FSP-T source code and there was no other debugging approaches in this phase. I suspected the issue would be caused by one of the following:
  1. Fsp-T parameter's pointer being passed to the TempRamInitApi
  2. the temporary RAM base wasn't correct
  3. there would be a problem in the microcode I was using,
since there wouldn't be any reason for the execution to not return if no.1 and 2 were the issues my suspicions made me focus on No. 3 since a buggy microcode would highly likely crash the processor. I must mention the first set of microcode mcbs used were meant for this platform but somehow they didn't work right. Turns out I guessed it right.

On Monday, December 30th, 2024 at 5:11 PM, memristor2 via groups.io <memristor2=proton.me@groups.io> wrote:
Any thoughts on this?
even the smallest hints would be highly appreciated.

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On Tuesday, December 24th, 2024 at 6:12 PM, memristor2 via groups.io <memristor2=proton.me@groups.io> wrote:


Hello everyone,
I am trying to  build an Intel platform's customized UEFI.
I have extracted the microcode and FSP binaries from the vendors UEFI image successfully. I also changed the PlatformPkg and FspFlashOffset FDF files. Execution goes on fine up until the last line of this subroutine:

FspHeaderFound:
  ; Get the fsp TempRamInit Api address
  mov eax, dword [edi + FSP_HEADER_IMAGEBASE_OFFSET]
  add eax, dword [edi + FSP_HEADER_TEMPRAMINIT_OFFSET]
  ; Setup the hardcode stack
  mov esp, TempRamInitStack
  ; Call the fsp TempRamInit Api
  jmp eax

I have checked the address of TempRamInit Entry which matched the address inside the FSP header.
but somehow it doesn't return to the TempRamInitDone subroutine. I have no idea why this happens. I also changed the UPD parameters to match the signature of the target platform.
Any thoughts on this?



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