Re: [patch 2/8] FatPkg\EnhancedFatDxe: Initialize variable after declaration

[Kurt Kennett <Kurt.Kennett@microsoft.com>]

Yes.  When I said "read-protect" I mean "protect by making it read-only".  I should have said "read-only protect" or "write-protect".

K2

-----Original Message-----
From: afish@apple.com [mailto:afish@apple.com] 
Sent: Thursday, December 8, 2016 4:37 PM
To: Kurt Kennett <Kurt.Kennett@microsoft.com>
Cc: Yao, Jiewen <jiewen.yao@intel.com>; Bi, Dandan <dandan.bi@intel.com>; edk2-devel@lists.01.org; Ni, Ruiyu <ruiyu.ni@intel.com>
Subject: Re: [edk2] [patch 2/8] FatPkg\EnhancedFatDxe: Initialize variable after declaration


> On Dec 8, 2016, at 4:26 PM, Kurt Kennett <Kurt.Kennett@microsoft.com> wrote:
> 
> Is the data 'variable'?  i.e does it ever change?
> 
> A normal compiler should put this data into a section marked read-only if it is marked as const, and a loader could read-protect the region after load.
> 

K2,

Did you mean write-protoect? 

FYI in my example in this thread from a macOS clang compiler the constant date ends up in a const TEXT section, as the text section in general is const. That is why the compiler emitted a PC relative access. This only ever becomes an issue when hand writing assemble code for X64. 

Thanks,

Andrew Fish 

> K2
> 
> -----Original Message-----
> From: Yao, Jiewen [mailto:jiewen.yao@intel.com]
> Sent: Thursday, December 8, 2016 3:47 PM
> To: Kurt Kennett <Kurt.Kennett@microsoft.com>; Bi, Dandan 
> <dandan.bi@intel.com>; edk2-devel@lists.01.org
> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>
> Subject: RE: [edk2] [patch 2/8] FatPkg\EnhancedFatDxe: Initialize 
> variable after declaration
> 
> Agree. Maybe we can move it to be a global variable ?
> 
> Thank you
> Yao Jiewen
> 
>> -----Original Message-----
>> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf 
>> Of Kurt Kennett
>> Sent: Friday, December 9, 2016 1:28 AM
>> To: Bi, Dandan <dandan.bi@intel.com>; edk2-devel@lists.01.org
>> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>
>> Subject: Re: [edk2] [patch 2/8] FatPkg\EnhancedFatDxe: Initialize 
>> variable after declaration
>> 
>> This seems kind of silly.
>> Why isn't this just const data?  This adds code and memory accesses 
>> that are worthless and happen on every call to the function.
>> 
>> K2
>> 
>> -----Original Message-----
>> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf 
>> Of Dandan Bi
>> Sent: Thursday, December 8, 2016 2:54 AM
>> To: edk2-devel@lists.01.org
>> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
>> Subject: [edk2] [patch 2/8] FatPkg\EnhancedFatDxe: Initialize 
>> variable after declaration
>> 
>> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
>> Contributed-under: TianoCore Contribution Agreement 1.0
>> Signed-off-by: Dandan Bi <dandan.bi@intel.com>
>> ---
>> FatPkg/EnhancedFatDxe/Misc.c | 14 +++++++++++++-
>> 1 file changed, 13 insertions(+), 1 deletion(-)
>> 
>> diff --git a/FatPkg/EnhancedFatDxe/Misc.c 
>> b/FatPkg/EnhancedFatDxe/Misc.c index f91759c..6ad688c 100644
>> --- a/FatPkg/EnhancedFatDxe/Misc.c
>> +++ b/FatPkg/EnhancedFatDxe/Misc.c
>> @@ -696,15 +696,27 @@ Returns:
>>   TRUE                  - The time is valid.
>>   FALSE                 - The time is not valid.
>> 
>> --*/
>> {
>> -  static UINT8  MonthDays[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 
>> 31, 30, 31 };
>> +  STATIC UINT8  MonthDays[12];
>>   UINTN         Day;
>>   BOOLEAN       ValidTime;
>> 
>>   ValidTime = TRUE;
>> +  MonthDays[0] = 31;
>> +  MonthDays[1] = 28;
>> +  MonthDays[2] = 31;
>> +  MonthDays[3] = 30;
>> +  MonthDays[4] = 31;
>> +  MonthDays[5] = 30;
>> +  MonthDays[6] = 31;
>> +  MonthDays[7] = 31;
>> +  MonthDays[8] = 30;
>> +  MonthDays[9] = 31;
>> +  MonthDays[10] = 30;
>> +  MonthDays[11] = 31;
>> 
>>   //
>>   // Check the fields for range problems
>>   // Fat can only support from 1980
>>   //
>> --
>> 1.9.5.msysgit.1
>> 
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