Running Java programs in gem5(or any language which is not C)

Question

This may be a silly question, but i\'m learning about gem5 recently and i\'m being able to simulate my C programs using this software, in syscall emulation and in full system si

Answer 1

You execute Java programs exactly the same way you execute C programs:

• Gem5 doesn't understand C, so if you want to execute a C program, you first need to compile it to a language Gem5 understands, or you need to interpret it in an interpreter that is written in a language Gem5 understands.
• Gem5 doesn't understand Java, so if you want to execute a Java program, you first need to compile it to a language Gem5 understands, or you need to interpret it in an interpreter that is written in a language Gem5 understands.

Here are a couple of possibilities I can think of:

• use a native code compiler to compile Java to Alpha, ARM, Sparc, or x86 native machine code,
• use a Java interpreter written in (or compiled to) Alpha, ARM, Sparc, or x86 native machine code to interpret that Java code,
• use a JVM compiler to compile Java to JVM bytecode, then use a JVM written in (or compiled to) Alpha, ARM, Sparc, or x86 native machine code to interpret that JVM bytecode, or
• use a JVM compiler to compile Java to JVM bytecode, then use a native code compiler to compile the JVM bytecode to Alpha, ARM, Sparc, or x86 native machine code.

It is, of course, possible to chain and/or mix any number of the above.

Answer 2

Similar post: Is it possible to run java -jar on gem5 simulator with ISA x86?

A full system Ubuntu image will almost certainly work (pre-install Java with QEMU user mode before running gem5).

X86 syscall emulation could in theory just work, the command line would be something like:

build/X86/gem5.opt \
  configs/example/se.py \
  --cmd /usr/bin/java \
  --options HelloWorld \
  --param 'system.cpu[0].workload[:].release = "5.2.1"' \

where /usr/bin/java is the Java interpreter ELF executable just like your C program, and HelloWorld.class is the compiled Java class passed as an argument to java.

However, I tried this on Ubuntu 18.04 and gem5 61005bb9ef455b2ac851f8a992f2cec5686e520f and it failed with:

/usr/bin/java: error while loading shared libraries: libjli.so: cannot open shared object file: No such file or directory

I'm not sure why that was the case, it would require further investigation.

Analogous for Python: Is it possible to run Python code in Gem5 syscall emulation mode?