[ros-dev] [ros-diffs] [fireball] 34232: Yuri Sidorov<jura at cp-lab.com> - Prevent boolean flags from beingoptimized away by compiler (due to PSEH usage) by making themvolatile. See issue #3408 for more details.

[Yury Sidorov]

Hi,

It's corner case problem and it occurs only in these functions.

Code:

BOOLEAN f = FALSE;

f = TRUE;
call_some_func();
f = FALSE;

gcc optimizer removes TRUE/FALSE assignments, since it knows that f 
was FALSE before this code block and remains FALSE after. gcc knows 
nothing about exceptions and SEH and performs such optimizations 
here...

Yury Sidorov.

----- Original Message ----- 
From: "Alex Ionescu" <ionucu at videotron.ca>
To: <ros-dev at reactos.org>
Sent: Tuesday, July 01, 2008 9:28 PM
Subject: Re: [ros-dev] [ros-diffs] [fireball] 34232: Yuri 
Sidorov<jura at cp-lab.com> - Prevent boolean flags from beingoptimized 
away by compiler (due to PSEH usage) by making themvolatile. See issue 
#3408 for more details.


> What?
>
> Why would the compiler optimize these away? This doesn't make any 
> sense.
>
> If something is happening to these flags, PSEH should be fixed --  
> not
> making every flag in the source base a volatile.
>
> On 1-Jul-08, at 3:48 AM, fireball at svn.reactos.org wrote:
>
>> Author: fireball
>> Date: Tue Jul  1 05:48:50 2008
>> New Revision: 34232
>>
>> URL: http://svn.reactos.org/svn/reactos?rev=34232&view=rev
>> Log:
>> Yuri Sidorov <jura at cp-lab.com>
>> - Prevent boolean flags from being optimized away by compiler (due
>> to PSEH usage) by making them volatile.
>> See issue #3408 for more details.
>>
>> Modified:
>>    trunk/reactos/ntoskrnl/mm/virtual.c
>>
>> Modified: trunk/reactos/ntoskrnl/mm/virtual.c
>> URL: 
>> http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/mm/virtual.c?rev=34232&r1=34231&r2=34232&view=diff
>> =
>> =
>> =
>> =
>> =
>> =
>> =
>> =
>> ======================================================================
>> --- trunk/reactos/ntoskrnl/mm/virtual.c [iso-8859-1] (original)
>> +++ trunk/reactos/ntoskrnl/mm/virtual.c [iso-8859-1] Tue Jul  1
>> 05:48:50 2008
>> @@ -70,7 +70,7 @@
>>     PFN_NUMBER MdlBuffer[(sizeof(MDL) / sizeof(PFN_NUMBER)) +
>> MI_MAPPED_COPY_PAGES + 1];
>>     PMDL Mdl = (PMDL)MdlBuffer;
>>     ULONG TotalSize, CurrentSize, RemainingSize;
>> -    BOOLEAN FailedInProbe = FALSE, FailedInMapping = FALSE,
>> FailedInMoving;
>> +    volatile BOOLEAN FailedInProbe = FALSE, FailedInMapping =
>> FALSE, FailedInMoving;
>>     BOOLEAN PagesLocked;
>>     PVOID CurrentAddress = SourceAddress, CurrentTargetAddress =
>> TargetAddress;
>>     PVOID MdlAddress;
>> @@ -225,7 +225,7 @@
>> {
>>     UCHAR StackBuffer[MI_POOL_COPY_BYTES];
>>     ULONG TotalSize, CurrentSize, RemainingSize;
>> -    BOOLEAN FailedInProbe = FALSE, FailedInMoving, HavePoolAddress
>> = FALSE;
>> +    volatile BOOLEAN FailedInProbe = FALSE, FailedInMoving,
>> HavePoolAddress = FALSE;
>>     PVOID CurrentAddress = SourceAddress, CurrentTargetAddress =
>> TargetAddress;
>>     PVOID PoolAddress;
>>     KAPC_STATE ApcState;
>>
>
> Best regards,
> Alex Ionescu
>
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