[Vm-dev] [OpenSmalltalk/opensmalltalk-vm] Restore support for large cursor on linux X11 VM (#424)

[David T. Lewis]

On Wed, Sep 04, 2019 at 01:59:21AM -0700, Nicolas Cellier wrote:
>  
> I committed the generated configure.
> I have a doubt, it seems that I set the `-DHAVE_LIBXRENDER` define if I find the header,
> then check whether the library libXrender.so is required or not (and add it to `LIBS` if required).
> 
> That does not cover the case when header would be present, but the library would be required AND absent. Should we cover that case?
>

For the case of a VM compiled with HAVE_LIBXRENDER, but running on a
machine that does not have the xrender library runtime, this could be
a problem.

In practice, I expect that any Linux machine with X11 will also provide
the runtime library for xrender, but that is just a guess.

To test this, I started with an interpreter VM compiled with Xrender
development libraries, and with large cursor support working. I then
removed (renamed) the following runtime libraries:

	/usr/lib/x86_64-linux-gnu/libXrender.a
	/usr/lib//x86_64-linux-gnu/libXrender.so
	/usr/lib/x86_64-linux-gnu/libXrender.so.1
	/usr/lib//x86_64-linux-gnu/libXrender.so.1.3.0

Result: The VM fails to run, and crashes:

	lewis at lewis-Gazelle-Pro:~/squeak/Squeak4.6$ squeak squeak.175
	libXrender.so.1: cannot open shared object file: No such file or directory
	could not find display driver vm-display-X11; either:
	  - check that /usr/local/lib/squeak/4.16.6-3772/vm-display-X11.so exists, or
	  - use the '-plugins <path>' option to tell me where it is, or
	  - remove DISPLAY from your environment.
	Aborted (core dumped)

Conclusion: If a VM with Xrender and large cursor support is run on
a machine that does not have the Xrender runtime libraries, it probably
will not work.

In my opinion, this is not a likely failure mode. I would expect that
machines that use X11 will also provide Xrender and other extensions
by default. But it could happen, so it is worth noting the risk.

Dave