Question

System V ABI says the first ___ integer/pointer arguments are passed in the following registers: What is assumed of these registers?

Answer 1

The System V ABI specifies that the first six integer or pointer arguments are passed in specific registers which leads to faster function calls. The involved registers are RDI, RSI, RDX, RCX, R8, and R9. They improve performance by avoiding the stack for initial arguments.

Step-by-step explanation:

The System V Application Binary Interface (ABI) specifies that the first six integer or pointer arguments are passed to functions via registers when using the x86-64 architecture. These registers are RDI, RSI, RDX, RCX, R8, and R9. This is an optimization that allows for faster function calls, as using registers is quicker than accessing the stack.

It is assumed that these registers will contain the values of the first six integer or pointer arguments when a function is called. The compiler generates code accordingly to follow this convention, and any called function knows to look in these registers for its arguments. If there are more than six arguments, the rest are typically passed on the stack.

This ABI convention is a key part of software development for systems programming and understanding it can help in debugging, optimizing, or interfacing with low-level code.