Hello World in s390x Assembly (Linux)

A simple Hello World implementation in IBM System z (s390x) assembly language for Linux systems. The s390x architecture represents IBM's mainframe lineage, designed for high-reliability computing environments with a focus on data processing and I/O operations.

Installation

On an s390x Linux system, you'll need the standard GNU toolchain:

sudo apt-get update
sudo apt-get install binutils gcc

Running

Assemble and link:

as -o main.o main.s
ld -o hello main.o
./hello

Code Explanation

The s390x architecture represents a different design philosophy from the RISC architectures we often see in modern systems. As a CISC (Complex Instruction Set Computing) architecture, it includes many sophisticated instructions and addressing modes, though our simple example only uses a few basic ones.

The implementation demonstrates several key aspects of s390x assembly:

Register Usage:

• General purpose registers are named %r0 through %r15
• %r1 holds the system call number
• %r2 through %r4 hold system call parameters
• Register pairs can be used for 128-bit operations (though not shown in this example)

Instructions Used:

• lghi (Load Halfword Immediate): Loads a 16-bit value into a 64-bit register with sign extension
• larl (Load Address Relative Long): Loads an address using PC-relative addressing
• svc (Supervisor Call): Makes a system call

Memory and Alignment:

• The .align 8 directive ensures 8-byte (64-bit) alignment
• The .section directive separates code (".text") from read-only data (".rodata")
• s390x uses big-endian byte ordering

System Call Convention:

• System call numbers are passed in %r1
• Parameters are passed in registers %r2 through %r7
• The svc 0 instruction triggers the system call

The s390x architecture has several unique characteristics:

• Support for both 31-bit and 64-bit addressing modes
• Hardware decimal arithmetic support
• Sophisticated I/O subsystem
• Built-in virtualization support
• Hardware-assisted cryptography

While our simple example doesn't showcase many of these advanced features, they make s390x particularly well-suited for its traditional role in enterprise computing, especially for tasks involving large-scale data processing and transaction handling.