What is Assembly Programming (and why do I care) ?

do I care)?

WHAT IS ASSEMBLY PROGRAMMING?

• All computer processors:
• Manages arithmetic, logic and control
• Different processor families have specific languages:
• Eg Intel Core, Advanced RISC Machine (ARM) etc
• Lowest level of human readable programming
• The “assembler” translates code into binary machine instructions
• Essentially bit strings that are interpretable by the processor

PROGRAMMING LANGUAGE HIERARCHY

C/C++, Pascal, Objective-C

Intel, ARM etc

Adapted from: https://blog.malwarebytes.com/security-world/2012/09/so-you-want-to-be-a-malware-analyst/

ASSEMBLY – WHY?

• Why do you need to know it?
• Write tiny / really fast programs
• No operating system to get in the way
• Write compilers
• Write drivers for custom hardware
• Find vulnerabilities in code.

• Why do you need to know it?
• Reverse-engineering binaries
• Eg., C/C++ compile to native machine code.
• No comments, variable names, control structures (if, loops). Really hard to figure out what is going on.
• All binaries can be disassembled to ASM!

RISC VERSUS CISC

• Processor instruction sets can be classified as CISC or RISC
• RISC: Reduced Instruction Set Computer
• Eg. ARM
• CISC: Complex Instruction Set Computer
• Eg. Intel

CISC

Complex Instruction Set RISC – Reduced Instruction Set Emphasis on hardware Emphasis on software Includes multi-clock complex (i.e. Single-clock, reduced instruction only specialised instructions) Small code size Large code sizes Instructions have variable cycle time Typical take one cycle More transistors typically used for storing Less transistors, typically used more for complex instructions memory registers Higher power usage Lower power usage Typically well suited to multimedia Typically well suited to low powered applications contexts (eg., mobile phones)

ARM ASSEMBLY PROGRAMMING

• Arm: Advanced RISC Machine
• The most widely used instruction set in the world:
• 130 billion ARM processors produced
• mobile devices, routers, IoT devices (eg RPi, Arduino)
• Consists of about 100 instructions in total:
• We will explore some but certainly not all

SUMMARY

• ASM programming represents the lowest level of human readable programming
• Near 1-to-1 match with machine instructions
• RISC versus CISC
• ASM programming is useful for:
• Hardware specific programming
• Optimising code for performance
• Reverse engineering and analysing code behaviour