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To: Jordan Justen <jordan.l.justen@intel.com>,
 edk2-devel-01 <edk2-devel@lists.01.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>, Ruiyu Ni <ruiyu.ni@intel.com>
References: <20171110154908.306-1-lersek@redhat.com>
 <20171110154908.306-2-lersek@redhat.com>
 <151059653162.20614.10956585129107897594@jljusten-skl>
From: Laszlo Ersek <lersek@redhat.com>
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Date: Mon, 13 Nov 2017 19:30:12 +0100
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 (mx1.redhat.com [10.5.110.29]); Mon, 13 Nov 2017 18:30:15 +0000 (UTC)
Subject: Re: [PATCH 1/4] OvmfPkg/Sec/Ia32: free up EAX for other uses while setting up the stack
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On 11/13/17 19:08, Jordan Justen wrote:
> On 2017-11-10 07:49:05, Laszlo Ersek wrote:
>> Currently EAX is used as an intermediary in setting ESP to
>> SEC_TOP_OF_STACK, and in passing SEC_TOP_OF_STACK to
>> SecCoreStartupWithStack() as the "TopOfCurrentStack" argument.
>>
>> In a later patch we'll use EAX differently, so replace it with EBX under
>> the current use.
>>
>> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>> ---
>>  OvmfPkg/Sec/Ia32/SecEntry.nasm | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/OvmfPkg/Sec/Ia32/SecEntry.nasm b/OvmfPkg/Sec/Ia32/SecEntry.nasm
>> index 7fee1c2b2e4f..54d074e621f6 100644
>> --- a/OvmfPkg/Sec/Ia32/SecEntry.nasm
>> +++ b/OvmfPkg/Sec/Ia32/SecEntry.nasm
>> @@ -40,8 +40,8 @@ ASM_PFX(_ModuleEntryPoint):
>>      ;
>>      %define SEC_TOP_OF_STACK (FixedPcdGet32 (PcdOvmfSecPeiTempRamBase) + \
>>                            FixedPcdGet32 (PcdOvmfSecPeiTempRamSize))
>> -    mov     eax, SEC_TOP_OF_STACK
>> -    mov     esp, eax
>> +    mov     ebx, SEC_TOP_OF_STACK
>> +    mov     esp, ebx
> 
> Can't you initialize the temp RAM before this code?

Should be possible, yes.

Thanks
Laszlo