+\subsection{Interacting with the Binary}
+
+Java source code can create a copy of the translated binary by instantiating the class generated by the binary translator or instantiating the interpreter. It can then interact with the process through the many facilities provided by the Runtime interface. Invoking the run() method of the Runtime interface will load the given arguments into the processÕs memory as invoke the binaries entry point (typically \_start() in crt0.o). This will pass control on to the main() function which will have the arguments passed to run() loaded into argv and argc.
+
+As the binary executes it often passes control back to the Runtime class through the MIPS {\tt SYSCALL} instruction. The interpreter and translated binaries invoke the {\tt syscall()} method of the Runtime class when the {\tt SYSCALL} instruction is executed. The Runtime class then can manipulate the processÕs environment (read and write to memory, modify the file descriptor table, etc) and interact with the rest of the JVM on behalf of the process (read and write to a file or stream, etc). There is even a syscall to pause the VM and temporarily return control to the caller.
+
+In addition to the interfaces provided by NestedVM, users can create their own interfaces between the MIPS and Java world. The Runtime provides a method called call() that will call a function by name in the MIPS binary. The call() method looks up the function name in the binaryÕs ELF symbol table and manipulating the stack and registers accordingly to execute the given function. This allows Java code to seamlessly invoke functions in the binary.
+
+{\footnotesize\begin{verbatim}
+// Java
+private Runtime rt = new MyBinary();
+public void foo(int n) {
+ for(int i=0;i<10;i++) {
+ int result = rt.call("do_work",i);
+ System.err.println("do_work(i) = " + result);
+ }
+}
+// C
+void do_work(int n) {
+ int i;
+ int ret=0;
+ for(i=0;i<n;i++) ret += i;
+ return n;
+}
+\end{verbatim}}
+
+The MIPS binaries can also invoke a special method of Runtime called callJava().When the MIPS binary invokes the {\tt CALL\_JAVA} syscall (usually done through the {\tt \_call\_java()} function provided by the NestedVM support library) the callJava() method in Runtime is invoked with the arguments passes to the syscall.
+
+{\footnotesize\begin{verbatim}
+// Java
+private Runtime rt = new MyBinary() {
+ pubilc int callJava(int a, int b, int c, int d) { System.err.println("Got " + a + " " + b);
+};
+public void foo() { rt.run(); }
+// C
+void main(int argc, char **argv) {
+ \_call\_java(1,2);
+}
+\end{verbatim}}
+
+These two methods can even be combined. MIPS can call Java through the CALL\_JAVA syscall, which can in turn invoke a MIPS function in the binary with the call() method.\r\r
+Users preferring a simpler communication mechanism can also use Java StreamÕs and file descriptors. Runtime provides a simple interface for mapping a Java Input or OutputStream to a File Descriptor.
+
+%Java source code can create a copy of the translated binary by
+%instantiating the corresponding class, which extends {\tt Runtime}.
+%Invoking the {\tt main()} method on this class is equivalent to
+%calling the {\tt main()} function within the binary; the {\tt String}
+%arguments to this function are copied into the binary's memory space
+%and made available as {\tt **argv} and {\tt argc}.
+
+%The translated binary communicates with the rest of the VM by
+%executing MIPS {\tt SYSCALL} instructions, which are translated into
+%invocations of the {\tt syscall()} method. This calls back to the
+%native Java world, which can manipulate the binary's environment by
+%reading and writing to its memory space, checking its exit status,
+%pausing the VM, and restarting the VM.
+
+
+%\subsection{Virtualization}
+
+%The {\tt Runtime} class implements the majority of the standard {\tt
+%libc} syscalls, providing a complete interface to the filesystem,
+%network socket library, time of day, (Brian: what else goes here?).
+
+%\begin{itemize}
+
+%\item ability to provide the same interface to CNI code and
+% NestedVMified code
+
+%\item security advantages (chroot the {\tt fork()}ed process)
+%
+%\end{itemize}
+
projects / nestedvm.git / blobdiff