[Vm-dev] 32bit clean VM work.

Philippe Marschall philippe.marschall at gmail.com
Sun Jun 10 10:35:13 UTC 2007

You make me want to buy a Mac.


2007/6/10, John M McIntosh <johnmci at smalltalkconsulting.com>:
> Some of you might know that David T. Lewis has been working on
> changes to the VM source to make it work fully within 32 or 64 bit
> address spaces.
> As we know the Squeak VM treated memory address which are unsigned
> values as signed integer values. This wrong usage of signed math in
> compare statments or do loops which would cause the VM to make an
> incorrect decision resulting in corrupted memory and causing the VM
> to crash.
> This issue would usually occur if you wanted to use 1GB of memory for
> your VM and the host operating system would then allocate memory for
> you above the 2GB boundary, or at say the 1.5GB boundary. Resulting
> either in an instant crash, or a crash much later when your memory
> needs caused the VM to grow over the 2GB boundary.
> Some fixes were done in the past to make the VM mostly run when fully
> over the 2GB boundary but at best they were insufficient patches.
> Over the last couple of days I reviewed David Lewis' changes, plus
> made some fixes, and revised the macintosh os-x support files, plus
> worked up some general test cases to see what happens when you run
> the macro bench marks below the 2GB boundary, crossing the 2GB
> boundary, and when the image is allocated at the 3GB boundary.
> This afternoon I'm pleased to say the VM passed all runs of my
> trivial test cases, so I have check in the Mac OS carbon source code
> changes and David's changes to the Mac OS source tree for further
> review.
> People wanting to build a VM should review the Mac OS build
> instructions to build a Mac OS carbon VM, or review the required
> changes to VMMaker as per the Carbon VM build readme to build a 32bit
> clean VM.
> I have not:
> (a) build a 64 bit VM and tested it.
> VM developers should consider the mmap call in the memory allocation
> routine, you can specify a suggested starting position. On OS-X I was
> able to chose  1GB, 1.5GB, 2GB and 3GB.  I have not tested 64bit VMs
> at the 0x8000000000000000 boundary.  I suspect you could allocate at
> the 0x7FFFFFFFF0000000 Then ask for 600MB of memory for the image.
> That would set the end of memory at 0x8000000015800000, 344MB over
> the negative sign boundary.
> (b) I have not tested or reviewed any of the external plugins for
> improper use of usqInt.
> (c) I have not confirmed the changes work with the Unix VM, or the
> Windows VM, I have no plans to do so.
> --
> ========================================================================
> ===
> John M. McIntosh <johnmci at smalltalkconsulting.com>
> Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
> ========================================================================
> ===

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