[Vm-dev] CameraPlugin segmentation fault on 64-bit Linux

[Ben Coman]

On Sun, Apr 30, 2017 at 2:21 AM, David T. Lewis <lewis at mail.msen.com> wrote:

>
> On Sat, Apr 29, 2017 at 10:08:23AM -0600, Daniel Drake wrote:
> > Hi Dave,
> >
> > On Sat, Apr 29, 2017 at 9:58 AM, David T. Lewis <lewis at mail.msen.com>
> wrote:
> > > I don't think that the camera plugin was ever made 64-bit clean. A bug
> report
> > > is at http://bugs.squeak.org/view.php?id=7816
> > >
> > > This would be a good project for an interested volunteer :-)
> >
> > I'm an interested volunteer, knowledgeable of 32 vs 64 bit challenges
> > but with no squeak-vm experience. Can you briefly provide some
> > direction of where to start here?
> >
> > Are there any other plugins that have previously been made 64-bit
> > clean? (Maybe there is a similar example in svn history and I can find
> > some direction from that.)
>
>
> Hi Daniel,
>
> Great, thanks for looking into this!
>
> SoundPlugin and SqueakSLL are examples of plugins that required updates
> for 64-bit.
>
> The majority of issues involve storage of 64-bit pointer values in 32-bit
> integers. Usually this is fixed by providing correct type declarations
> throughout the support code, and by making sure that the translated code
> from the plugin class in VMMaker produces code with type declarations
> that match the support code.
>
> In the case of CameraPlugin, I would be inclined to start by looking at
> the support code in platforms/unix/plugins/CameraPlugin/ to get an idea
> of what the function declarations are (or should be). Look through it
> for any type casts, usually these are a red flag for something you are
> going to need to fix.
>
> If everything looks good in platforms/[unix|win32|Moc OS|iOS] then the
> next thing to check will be the declarations in
> platforms/Cross/plugins/CameraPlugin/CameraPlugin.h. These will probably
> be ok, but make sure that anything declared as int is really a 32-bit
> integer value.
>
> If you are statisfied that the support code is all in good order for
> compiling on 64-bits, then take a look at CameraPlugin in your VMMaker
> image, and at it sgenerated source code in src/plugins/CameraPlugin/
> CameraPlugin.c.
>
> Look for places in the generated code where the support code functions
> are being called incorrectly, or where methods in the plugin itself
> use default sqInt variable declarations that should be explicitly
> declared as something else.
>
> I do this sort of work using an interpreter VM on a 64-bit Linux
> system because it lets me easily compile 64-bit VMs that run on
> 32-bit sqInt object memories, which is the combination that most
> reliably finds type declaration problems.
>
> You will probably want to run your VMs under gdb to locate problems,
> but don't be afraid to hack some printf's into your generated plugin
> source in order to find problems. Do a fflush after each printf
> so you can see the output right before your VM crashes.
>
> Thanks and HTH,
> Dave
>
>
Some general background info...

A Tour of the Squeak Object Engine
http://coweb.cc.gatech.edu/squeakbook/uploads/rowledge.pdf

Extending the Squeak Virtual Machine
http://sdmeta.gforge.inria.fr/FreeBooks/CollectiveNBlueBook/greenberg.pdf

cheers -ben
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