Re: [ros-dev] [ros-diffs] [jgardou] 54462: [RTL] - explicitly truncate some values, so it doesn't count as an error for compiler/MSVC runtime checker

[Timo Kreuzer]

That doesn't make much sense.
Whats the point of the LOWORD() macro, if not truncating it ?
Fix the macro if its broken.

Am 20.11.2011 20:45, schrieb [e-mail]:
> Author: jgardou
> Date: Sun Nov 20 19:45:06 2011
> New Revision: 54462
>
> URL: http://svn.reactos.org/svn/reactos?rev=54462&view=rev
> Log:
> [RTL]
> explicitly truncate some values, so it doesn't count as an error for compiler/MSVC runtime checker
>
> Modified:
>      trunk/reactos/lib/rtl/image.c
>
> Modified: trunk/reactos/lib/rtl/image.c
> URL: http://svn.reactos.org/svn/reactos/trunk/reactos/lib/rtl/image.c?rev=54462&a...
> ==============================================================================
> --- trunk/reactos/lib/rtl/image.c [iso-8859-1] (original)
> +++ trunk/reactos/lib/rtl/image.c [iso-8859-1] Sun Nov 20 19:45:06 2011
> @@ -369,7 +369,7 @@
>   {
>       SHORT Offset;
>       USHORT Type;
> USHORT i;
> ULONG i;
>  PUSHORT ShortPtr;
>  PULONG LongPtr;
>  PULONGLONG LongLongPtr;
>
> @@ -379,7 +379,6 @@
>           Offset = SWAPW(*TypeOffset)&  0xFFF;
>           Type = SWAPW(*TypeOffset)>>  12;
>           ShortPtr = (PUSHORT)(RVA(Address, Offset));
>     /*
>     * Don't relocate within the relocation section itself.
>     * GCC/LD generates sometimes relocation records for the relocation section.
>
> @@ -398,16 +397,16 @@
>               break;
>       case IMAGE_REL_BASED_HIGH:
>        *ShortPtr = HIWORD(MAKELONG(0, *ShortPtr) + (LONG)Delta);
>        *ShortPtr = HIWORD(MAKELONG(0, *ShortPtr) + (Delta&  0xFFFFFFFF));
>         break;
>
>     case IMAGE_REL_BASED_LOW:
>        *ShortPtr = SWAPW(*ShortPtr) + LOWORD(Delta);
>        *ShortPtr = SWAPW(*ShortPtr) + LOWORD(Delta&  0xFFFF);
>         break;
>
>     case IMAGE_REL_BASED_HIGHLOW:
>         LongPtr = (PULONG)RVA(Address, Offset);
>        *LongPtr = SWAPD(*LongPtr) + (ULONG)Delta;
>        *LongPtr = SWAPD(*LongPtr) + (Delta&  0xFFFFFFFF);
>         break;
>
>     case IMAGE_REL_BASED_DIR64:

[Jérôme Gardou]

Here the variable is an ULONGLONG and we pass it to a macro that casts 
it to a DWORD, and that's what it should do. Although casting and 
truncating is the same from a "normal" compiler point of view, a run 
time checker would raise a warning if you cast a value superior to 
0xFFFFFFFF to a DWORD. Truncating it explicitly tells it "yes, I 
truncate this value, not for avoiding compiler warning, but because 
that's what I want". See r54460 to see which kind of bugs such checkers 
could help to fix.

See also http://msdn.microsoft.com/en-us/magazine/cc301374.aspx for some 
in depth details, and, of course, cl documentation.
Also, gcc has this kind of functionalities, it's called GNAT.

Mit freundlichen Grüssen. :-)
Jérôme

Le 24/11/2011 00:03, Timo Kreuzer a écrit :
> That doesn't make much sense.
> Whats the point of the LOWORD() macro, if not truncating it ?
> Fix the macro if its broken.
>
> Am 20.11.2011 20:45, schrieb [e-mail]:
> > Author: jgardou
> > Date: Sun Nov 20 19:45:06 2011
> > New Revision: 54462
> >
> > URL: http://svn.reactos.org/svn/reactos?rev=54462&view=rev
> > Log:
> > [RTL]
> > explicitly truncate some values, so it doesn't count as an error
> >
> > for compiler/MSVC runtime checker
> >
> > Modified:
> >      trunk/reactos/lib/rtl/image.c
> >
> > Modified: trunk/reactos/lib/rtl/image.c
> > URL: 
> > http://svn.reactos.org/svn/reactos/trunk/reactos/lib/rtl/image.c?rev=54462&a...
> > ==============================================================================
> >
> > --- trunk/reactos/lib/rtl/image.c [iso-8859-1] (original)
> > +++ trunk/reactos/lib/rtl/image.c [iso-8859-1] Sun Nov 20 19:45:06 2011
> > @@ -369,7 +369,7 @@
> >   {
> >       SHORT Offset;
> >       USHORT Type;
> > USHORT i;
> > ULONG i;
> >  PUSHORT ShortPtr;
> >  PULONG LongPtr;
> >  PULONGLONG LongLongPtr;
> >
> > @@ -379,7 +379,6 @@
> >           Offset = SWAPW(*TypeOffset)&  0xFFF;
> >           Type = SWAPW(*TypeOffset)>>  12;
> >           ShortPtr = (PUSHORT)(RVA(Address, Offset));
> >     /*
> >     * Don't relocate within the relocation section itself.
> >     * GCC/LD generates sometimes relocation records for the 
> >
> > relocation section.
> > @@ -398,16 +397,16 @@
> >               break;
> >       case IMAGE_REL_BASED_HIGH:
> >        *ShortPtr = HIWORD(MAKELONG(0, *ShortPtr) + (LONG)Delta);
> >        *ShortPtr = HIWORD(MAKELONG(0, *ShortPtr) + (Delta&  
> >
> > 0xFFFFFFFF));
> >               break;
> >       case IMAGE_REL_BASED_LOW:
> >        *ShortPtr = SWAPW(*ShortPtr) + LOWORD(Delta);
> >        *ShortPtr = SWAPW(*ShortPtr) + LOWORD(Delta&  0xFFFF);
> >         break;
> >
> >     case IMAGE_REL_BASED_HIGHLOW:
> >         LongPtr = (PULONG)RVA(Address, Offset);
> >        *LongPtr = SWAPD(*LongPtr) + (ULONG)Delta;
> >        *LongPtr = SWAPD(*LongPtr) + (Delta&  0xFFFFFFFF);
> >         break;
> >
> >     case IMAGE_REL_BASED_DIR64:
>
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[Aleksey Bragin]

On 24.11.2011 3:27, Jérôme Gardou wrote:
>        *ShortPtr = SWAPW(*ShortPtr) + LOWORD(Delta);
>        *ShortPtr = SWAPW(*ShortPtr) + LOWORD(Delta&  0xFFFF); 

Maybe turn off this "feature" of MSVC checker then? Excuse me, but it's 
literally a code pollution. Especially the above case, of firstly ANDing 
with 0xFFFF, and *then* applying LOWORD (which would not change anything 
at all).

Or, as Timo said, maybe fix the macro? Move the cast elsewhere, so at 
first you &, and only then cast?

WBR,
Aleskey.

[Jérôme Gardou]

Le 24/11/2011 09:04, Aleksey Bragin a écrit :
> On 24.11.2011 3:27, Jérôme Gardou wrote:
> >        *ShortPtr = SWAPW(*ShortPtr) + LOWORD(Delta);
> >        *ShortPtr = SWAPW(*ShortPtr) + LOWORD(Delta&  0xFFFF); 
>
> Maybe turn off this "feature" of MSVC checker then? Excuse me, but 
> it's literally a code pollution. Especially the above case, of firstly 
> ANDing with 0xFFFF, and *then* applying LOWORD (which would not change 
> anything at all).
>
> Or, as Timo said, maybe fix the macro? Move the cast elsewhere, so at 
> first you &, and only then cast?
>
> WBR,
> Aleskey.
>
> Ros-dev mailing list
> [e-mail]
> http://www.reactos.org/mailman/listinfo/ros-dev

This one is a mistake on my side.

And the macro is correct. The right thing to do is & and then casting, 
as you say.
BTW, this feature is of by default, you have to turn it on with the /RTC 
flag.

[Timo Kreuzer]

Am 24.11.2011 00:27, schrieb Jérôme Gardou:
> Truncating it explicitly tells it "yes, I truncate this value, not for 
> avoiding compiler warning, but because that's what I want". See r54460 
> to see which kind of bugs such checkers could help to fix.

What's next?
(Value & 0xFFFF) -> warning because ANDing an ULONG64 is regarded as 
"silencing a warning" -> fix: 
__really_truncate_this_unsigned_int64_to_ushort_and_discard_lost_bits(Value); 
?

For me casting *is* already doing it "explicitly". And if someone 
doesn't know that casting is the same as truncating, he shouldn't do C 
coding.

I agree with Aleksey: turn this feature off, its a bit too much.

Timo