run: zero pad hello.py to succeed on OKL4

Fixes #804.

libports/run/python.run

@@ -52,7 +52,22 @@ install_config $config
 # Boot modules
 #
 
-exec cp [genode_dir]/libports/src/test/python/hello.py bin/
+# Fill up hello.py with zeros, otherwise on OKL4 it fails on native machines.
+# OKL4 bootstrap procedure loads the script to the designated address but does
+# not clear the remainder of the page. Hence, the script is followed by some
+# garbage, which the interpreter tries to execute.
+
+set test_file "[genode_dir]/libports/src/test/python/hello.py"
+set file_size [exec du -b $test_file]
+set file_size [regexp -inline {[0-9]+} $file_size]
+set file_size [expr 4096 - $file_size]
+catch { exec dd if=/dev/zero of=bin/hello.py.tmp bs=1 count=$file_size}
+exec cp  $test_file bin/hello.py
+exec cat bin/hello.py.tmp >>bin/hello.py
+exec rm  bin/hello.py.tmp
+set file_size [exec du -b bin/hello.py]
+set file_size [regexp -inline {[0-9]+} $file_size]
+if {$file_size != 4096 } { puts "hello.py could not be prepared properly"; exit 1 }
 
 # generic modules
 set boot_modules {