[Vm-dev] VM Maker: VMMaker.oscog-eem.1426.mcz

[David T. Lewis]

On Sat, Jul 18, 2015 at 06:09:22PM -0700, Eliot Miranda wrote:
>  
> Hi David,
> 
> On Sat, Jul 18, 2015 at 3:49 PM, David T. Lewis <lewis at mail.msen.com> wrote:
> 
> >
> > On Sat, Jul 18, 2015 at 08:55:27PM +0000, commits at source.squeak.org wrote:
> > >
> > > Eliot Miranda uploaded a new version of VMMaker to project VM Maker:
> > > http://source.squeak.org/VMMaker/VMMaker.oscog-eem.1426.mcz
> > >
> > > ==================== Summary ====================
> > >
> > > Name: VMMaker.oscog-eem.1426
> > > Author: eem
> > > Time: 18 July 2015, 1:54:29.051 pm
> > > UUID: 94ab92ba-c5c4-4953-8566-a4cd9c38df1f
> > > Ancestors: VMMaker.oscog-eem.1425
> > >
> > > Fix at least one set of 64-bit issues caused by Slang.  In particular
> > the integerObjectOf: code resulted in (objectMemory integerObjectOf:
> > MillisecondClockMask) evaluating to the -1 object, instead of the
> > 16r1FFFFFFF object, which was the cause of the initially nresponsive 64-bit
> > image on the real VM (no problem in the simulator).
> > >
> >
> > I can't test now to verify, but I wonder if this change is fixing the
> > right problem.
> >
> 
> I'm pretty sure it is.  It only bites in a 64-bit implementation with >
> 31-bit integers.  In the "standard" 64-bit image SmallIntegers are still
> only 31-bits so the issue never occurs.  The issue is that the default type
> of an integer constant in C is int.  So if one has to shift any constant
> such that a non-zero bit will occupy bit 31 (0 relative), it must be cast
> to a long type to avoid sign extension.

I don't see it. The size of SmallInteger is enforced by the image, not by
the object memory. There is nothing in the "standard" 64-bit image format
that requires small integers to be restricted to the same limits imposed
by a 32-bit object memory.

The #integerObjectOf: method answers a sqInt, which may be either 32 or
64 bits. This should just work, and I don't see a need for conditional
logic other than what might be needed to define the size of sqInt in the
first place.

> 
> Now of course I could generate all Integer constants with the L or UL
> suffix, e.g.
> 
> #define MillisecondClockMask 0x1FFFFFFFL
> 
> instead of
> 
> #define MillisecondClockMask 0x1FFFFFFF
> 
> but that's a much more pervasive change than only generating the cast in
> integerObjectOf when on 64-bits.  So I'm happy with the change that I've
> made.  Experience can of course prove me wrong...

I don't see the problem. Interpreter class>>initialize does this:
	MillisecondClockMask := 16r1FFFFFFF.

This works for all combinations or 32 and 64 bit image and host platform.

There should be no need to generate all of the integer constants with
L or UL suffix. It is perfectly acceptable to assign 16r1FFFFFFF to a
64 bit signed or unsigned variable, and no special handling should be
required.

I may be missing something, but I do not see anything about the Spur
64-bit image format that should require special handling for this.

Dave