Re: [ros-dev] [ros-diffs] [fireball] 34232: Yuri Sidorov<[e-mail]> - 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(a)videotron.ca>
To: <ros-dev(a)reactos.org>
Sent: Tuesday, July 01, 2008 9:28 PM
Subject: Re: [ros-dev] [ros-diffs] [fireball] 34232: Yuri 
Sidorov<jura(a)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(a)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(a)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=…
> >  =
> >  =
> >  =
> >  =
> >  =
> >  =
> >  =
> >  =
> >  ======================================================================
> >  --- 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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