The vminfo tool prints information about the program's environment, i.e. the VM and the parent program (if any.)
The following information is printed:
- Initial register values
- Process info table contents
- Syscall table contents
- Command-line arguments
- Environment variables
- Free memory regions
This tool is not part of the core bootstrap but it is nevertheless written directly in hexadecimal bytecode. There are several reasons for this:
- It can be used to help debug a VM before running the Onramp bootstrap process.
- It can print information that is not accessible to C such as initial register values.
- It can be run in all versions of the Onramp VM (though it may print less information on very old versions.)
The tool prints most numbers in both hexadecimal and decimal. In some cases the decimal representation assumes numbers are in signed two's complement. This is not a requirement of the VM spec; the VM only needs to implement unsigned math. We just assume for convenience that large unsigned numbers are best represented as negative decimals.
This tool can also be used to see what parent programs pass to their children. For example, to see the environment of a program running under the shell:
echo 'onrampvm output/final/bin/vminfo.oe a b c' | onrampvm output/configure/sh/sh.oe /dev/stdin
Or, to see the environment of a subprogram of cc:
touch /tmp/a.c && onrampcc -with-cpp=output/final/bin/vminfo.oe /tmp/a.c -o /tmp/a.oe
(Of course this latter command will fail, but not before printing the environment used to run the preprocessor.)
This can be useful to see the command-line arguments, proxied syscalls, and so on.