CPSC 355 Class Notes PDF

Welcome to your assembly bible, please pass this on to your friends and remember we’re all here to help each other out Course Objectives - Learn how a typical modern computer is structured - I.e. its architecture - Will concentrate on CPU architecture - Lear...

Welcome to your assembly bible, please pass this on to your friends and remember we’re all here to help each other out Course Objectives - Learn how a typical modern computer is structured - I.e. its architecture - Will concentrate on CPU architecture - Learn how a computer operates as it executes instructions - I.e the fetch-execute cycle - Learn how data and instructions are represented internally in a computer - Signed and unsigned integers - Characters and strings - Floating-point numbers - Machine instructions - Learn how to write programs in an assembly language - Often needed for creating: - Embedded systems - OS kernels - Device drivers - Code generator part of a compiler - Applications (rare today) - Useful for: - Nothing - Understanding a computer’s architecture - Understanding the details of Operating Systems - Writing more efficient high-level programs - Understand the connection between high-level languages and machine operation - Learn another high-level language (C) - Learn how to mix assembly code and C code Computer Architectures and Assembly Language Programming High-Level Architecture - A basic computer system consists of: - CPU - System clock - Primary memory - Also called Random Access Memory (RAM). Welcome to your assembly bible, please pass this on to your friends and remember we’re all here to help each other out - Secondary memory - Usually on a HDD/SSD - Peripheral input and output - Keyboard, monitor - Bus CPU - Is the “brains” of any computer system - Executes instructions - Controls the transfer of data across the bus - Is usually contained on a single microprocessor chip - Consists of 3 main parts: - Control Unit (CU) - Arithmetic Logic Unit (ALU) - Registers - will vary from architecture to architecture. May be dozens to hundreds CLICK TO EXPAND Assembly Code: - Note: argc in in w0, and argv[] is in x1 for main() define(i_r, w19) define(argc_r, w20) define(argv_r, x21) fmt:.string “%s\n”.balign 4  Welcome to your assembly bible, please pass this on to your friends and remember we’re all here to help each other out.global main main: stp x29, x30, [sp, -16]! mov x29, sp mov argc_r, w0 //copy argc mov argv_r, x1 //copy argv mov i_r, 0 b test top: adrp x0,fmt //set up 1st arg add x0, x0, :lo12:fmt ldr x1, [argv_r, i_r, SXTW 3] //set up 2nd arg bl printf add i_r, i_r, 1 test: cmp i_r, argc_r b.lt top ldp x29, x30, [sp], 16 ret Separate Compilation: - Source code is often divided into several modules(compilation units) - ie. separate.c or.s files - Makes development of large projects easier - Modules can be compiled into relocatable object code - Will be put into corresponding.o files - E.g: gcc -c myfile1.c produced myfile1.o - Object code is linked together to create an executable - Is done by ld(loader), which is usually invoked by gcc as the final step in the compilation process - E.g: gcc myfile1.o myfile2.o -o myexec - ld resolves any references to external data or functions in other modules - Code and data are relocated in memory as necessary to form contiguous text, data, and bss sections Separate Compilation and Linking: - Assembly code: first.s.balign 4.global main main: stp x29, x30, [sp, -16]! mov x29, sp adrp x19, a_m ← refers to objects in other modules ldr w0, [x19] bl myfunc ← refers to objects in other modules ldp x29, x30, 16 ret - Assembly code: second.s.global a_m a_m:.word 44 //global constant  Welcome to your assembly bible, please pass this on to your friends and remember we’re all here to help each other out.balign 4.global myfunc myfunc: stp x29, x30, [sp, -16]! mov x29, sp sub w0, w0, 1 ldp x29, x30, [sp], 16 ret - To Assemble and link: as first.s -o first.o as second.s -o second.o gcc first.o second.o -o myexec - Note: this can be done using a makefile C code can call functions written in assembly - Can be useful when optimizing sections of code - E.g - C code: mymain.c #include int sum (int, int); //function prototype: need to define for assembler to know int main() { int i=5, j=10, result; result = sum(i, j); printf(“result = %d\n”, result); return 0; } - Assembly code: sum.s.balign4.global sum sum: stp x29, x30, [sp, -16]! mov x29, sp add w0, w0, w1 ldp x29, x30, [sp], 16 ret - To compile and link: gcc -c mymain.c as sum.s -o sum.o gcc mymain.o sum.o -o myprog - To execute:./myprog result = 15 Assembly code can call functions written in C - E.g: - C code: sum.c int sum(int a, int b){ return a+b }  Welcome to your assembly bible, please pass this on to your friends and remember we’re all here to help each other out - Assembly code: mymain.s i_size= 4 j_size= 4 result_size = 4 alloc = -(16+i_size+j_size_result_size)&-16 dealloc = -alloc i_s = 16 j_s = 20 result_m = 24 //starting addresses fmt..string “result = %d\n”.balign 4 main: stp x29, x30, [sp, alloc]! mov x29, sp mov w19, 5 str w19, [x29, i_s] mov w19, 10 str w19, [x29, j_s] ldr w0, [x29, i_s] ldr w1, [x29, j_s] bl sum