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.

[Alex Ionescu]

Then gcc or PSEH should be fixed, not worked-around.

On 1-Jul-08, at 12:03 PM, Yury Sidorov wrote:
> 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" [e-mail]
> To: [e-mail]
> Sent: Tuesday, July 01, 2008 9:28 PM
> Subject: Re: [ros-dev] [ros-diffs] [fireball] 34232: Yuri
> [e-mail] - 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, [e-mail] 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 [e-mail]
> > > 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=3...
> > > =
> > > =
> > > =
> > > =
> > > =
> > > =
> > > =
> > > =
> > > =
> > > =
> > > ====================================================================
> > > --- 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
> >
> > Ros-dev mailing list
> > [e-mail]
> > http://www.reactos.org/mailman/listinfo/ros-dev
>
> Ros-dev mailing list
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Best regards,
Alex Ionescu