Syscalls for Rustaceans!

by Gargi Sharma
github.com/gs0510   

Follow the slides: tiny.cc/rustrace

What even is a systems programming language?

1970s:Improving on Assembly

"A system program is
an integrated set of
subprograms ...
exceeding some
threshold of size
and/or complexity."

1970s:

• The system program is likely to be used to support other software programs.


• It is designed for continued “production” use rather than a one-shot solution to a single applications problem.

1970s:

A language which can be used without undue concern for bit twiddling.

1990s:Rise of Scripting languages

1990s:

Rise of Scripting languages

• Bash, languages like Perl, Python, Ruby, Javascript etc. worked their way into the mainstream.
• Systems programming languages designed to build more primitive computer elements.
• Scripting languages are designed for gluing.

2010s:Boundaries Blur

2010s:

Boundaries Blur

• Dropbox was able to build surprisingly large and scalable systems on just Python.
• Javascript is used to render real-time, complex UIs in billions of web pages.
• Gradual typing has gained steam in Javascript, Python, etc. enabling a transition from “prototype” code to “production” code.

What is a systems programming language today?

Where does Rust shine?

Systems programming is
programming where
you spend more time reading man pages than reading the internet.

Writing our own strace!

System Calls!

Syscalls!

Around 330 system calls in Linux:

• File Access - creat, read, write, open, close, etc.
• Process Control - wait, waitpid , kill, fork, etc.
• Network Access - socket, getsockopt , listen, etc.

What happens when a syscall occurs?

What happens when a syscall occurs?

Making a syscall.

• Setup register with syscall number & parameters.
• Send a trap to kernel.
• Result stored in register.

What is strace?

• A diagnostic, debugging and instructional userspace utility for Linux.
• Invaluable for solving problems with programs for which the source is not readily available.

What is strace?

        fn main() {
          println!("Hello RustConf!");
        }
        

What is strace?

Writing our own strace.

• How to observe another process?
• How to trap a system call?
• How to fetch register values?

How to observe a process?

ptrace!!

How to observe a process?

        let output = cmd.before_exec(ptrace::traceme());
          
        let mut child = cmd.spawn();
        

How to trap a system call?

How to trap a system call?

        ptrace(
          Request::PTRACE_SYSCALL,
          pid,
          ptr::null_mut(),
          ptr::null_mut(),
        );

        waitpid(pid, None);
        

How to fetch register values?

        let res = ptrace::ptrace(
          Request::PTRACE_GETREGS,
          pid,
          PT_NULL as *mut c_void,
          &mut regs as *mut _ as *mut c_void,
        );
        

DEMO!

Conclusion 😊

Thank you!