> - Run the VM under gdb and let it crash. Try to investigate from there,
> in particular try to print the call stacks (don't remember what the
> magic invocation is). The VM implements both, printCallStack() to print
> the active call stack and printAllStacks() which prints all the call
> stacks (but I'm not sure which of those is supported in 3.7).

It crashed in gdb but after only ~7 hours (so it's not clear this is
the same issue). But here is the stack:

Program received signal SIGPIPE, Broken pipe.
0xb7e8f2ce in __write_nocancel () from /lib/tls/libc.so.6

gdb>backtrace

#0  0xb7e8f2ce in __write_nocancel () from /lib/tls/libc.so.6
#1  0x080e8936 in sqSocketSendDataBufCount (s=0xb5aaa624,
    buf=0xb5b3c3f4 "Content-Type:
image/gif;\r\n\tname=\"orprxh.gif\"\r\nContent-ID:
<orprxh.gif at 2D967531.ECA1AA47>\r\nContent-Transfer-Encoding:
base64\r\n\r\nR0lGODlh+gHYAbMAAAAADoQAAACCAAAAfNNhDXyOxvj56/ALCgcN///2/w",
'A' <repeats 15 times>..., bufSize=2077) at
/home/ajr/Squeak-3.9-7/platforms/unix/plugins/SocketPlugin/sqUnixSocket.c:1067
#2  0x080e661c in primitiveSocketSendDataBufCount ()
    at /home/ajr/Squeak-3.9-7/platforms/unix/src/vm/intplugins/SocketPlugin/SocketPlugin.c:1046
#3  0x0805bb77 in dispatchFunctionPointer (aFunctionPointer=0x80e64a0)
    at /home/ajr/Squeak-3.9-7/platforms/unix/src/vm/interp.c:3949
#4  0x08064305 in primitiveExternalCall () at
/home/ajr/Squeak-3.9-7/platforms/unix/src/vm/interp.c:14208
#5  0x0805bb77 in dispatchFunctionPointer (aFunctionPointer=0x8064230)
    at /home/ajr/Squeak-3.9-7/platforms/unix/src/vm/interp.c:3949
#6  0x0806d796 in interpret () at
/home/ajr/Squeak-3.9-7/platforms/unix/src/vm/interp.c:7756
#7  0x0805a5c9 in main (argc=1953394499, argv=0x0, envp=0x65707954)
    at /home/ajr/Squeak-3.9-7/platforms/unix/vm/sqUnixMain.c:1388