Calling C from Assembly
Understand how to invoke C functions from within your assembly code, adhering to the standard calling conventions.
Bridge Assembly & C
Why would you want to combine C and Assembly code? It's a powerful technique in low-level and system programming!
- Assembly: Great for performance-critical tasks, direct hardware access, and understanding system internals.
- C: Offers high-level structure, portability, and access to vast libraries.
By calling C functions from Assembly, you can leverage C's complex logic and libraries while retaining Assembly's low-level control for specific tasks.
The Calling Contract
When one function calls another, they need to agree on a set of rules. This 'contract' is known as a calling convention.
It defines crucial aspects of how functions interact:
- How arguments are passed (e.g., on the stack, in registers).
- The order in which arguments are passed.
- Which function is responsible for cleaning up the stack after the call.
- How return values are transmitted back to the caller.
Without these conventions, your assembly code wouldn't know how to prepare data for a C function, or how to interpret its results.