The Journey Before main()

6 months ago

The article explores the process between the kernel being asked to run a program and the execution of the program's main function.
The execve system call on Linux is used to signal the kernel to start loading a program, requiring the executable file's path, arguments, and environment variables.
Higher-level language wrappers, like Rust's Command::new, handle path resolution similar to shells but the kernel requires a full path.
Executable files on Linux use the ELF format, which includes headers and sections like .text (code), .data (initialized variables), and .bss (uninitialized variables).
ELF files support dynamic linking through sections like the Procedure Linkage Table (PLT), allowing shared libraries like libc to be loaded at runtime.
The kernel sets up the program's stack, which includes arguments (argv), environment variables (envp), and the ELF auxiliary vector (auxv) for system information.
The entry point of a program is typically the _start function, which initializes the runtime before calling the main function.
Different programming languages have varying runtime initialization processes, with languages like Rust and C having minimal setups compared to heavier runtimes like Java or Python.

Hasty Briefsbeta