ITEC 352 Lecture 20 JVM Intro

Functions + Assembly Review Questions? Project due today Activation record –How is it used?

Functions + Assembly Outline Functions in assembly Intro to JVM

Functions + Assembly Java Virtual Machine Architecture

Functions + Assembly

A Java Class File

Functions + Assembly A Java Class File (2)

Functions + Assembly A Java Class File (Cont’) Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring 0 bipush: push into stack Istore_1: pop the top of the stack and store the value in local variable at index “1”. Background: local variables are converted into array indices. iload_1: push the value at array index 1 into stack.

Functions + Assembly Byte Code LocationCodeMnemonicMeaning 0x00e30x10bipushPush next byte onto stack 0x00e40x0f15Argument to bipush 0x00e50x3cistore_1Pop stack to local variable 1 0x00e60x10bipushPush next byte onto stack 0x00e70x099Argument to bipush 0x00e80x3distore_2Pop stack to local variable 2 0x00e90x03iconst_0Push 0 onto stack 0x00ea0x3eistore_3Pop stack to local variable 3 0x00eb0x1biload_1Push local variable 1 onto stack 0x00ec0x1ciload_2Push local variable 2 onto stack 0x00ed0x60iaddAdd top two stack elements 0x00ee0x3eistore_3Pop stack to local variable 3 0x00ef0xb1returnReturn

Functions + Assembly Assembly process Translation of Assembly code into Machine language. Recall: –Every assembly instruction is represented as a 32 bit machine instruction. –Since there are different types of assembly instructions (e.g., arithmetic instructions, branch instructions etc.), There are also different way of using the 32 bits to represent machine instructions. –These different ways of packing 32 bits of machine code are called Instruction formats.

Functions + Assembly Examples Consider the following two usages of the load (ld) instruction: ld [x], %r1 Meaning: Load from a memory address specified as a constant value (in this case x) plus the contents of register %r0 into register %r1. ld %r1, %r2, %r3 Meaning: Load from memory address obtained by adding the values of registers %r1 and %r2 into the register %r3 In the first instruction we are using a constant value (memory address x). Whereas in the second we are using registers. Hence, there are two memory instruction formats in Machine code. (on next slide)

Functions + Assembly Memory instruction formats in machine code Instruction ld %r1, %r2, %r3 is represented as follows: rd: Destination register (%r3) ; op3: ld (11), rs1: first source register (%r1), rs2: second source register. Instruction ld [x], %r1 is represented as follows: rd: Destination register (%r1) ; op3: ld (11), rs1: first source register (%r0 ) (Here, %r0 is assumed to be there implicitly) simm13: address “x”. This should fit into 13 bits.

Functions + Assembly Complete ARC Instruction and PSR Formats Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Assembly to machine code translation Given an instruction: ld [x], %r1 The assembly process pattern matches this instruction with machine formats to obtain the machine code. E.g., After it sees the instruction, it maps it to the second memory format (the one with simm13). It then converts the instruction as follows: ldop3: 11 (op3 = 11) [x]simm13: Memory address x. If.org 2048, then x = In binary = %r0rs1 ( source register) (address = 00000) 5 bits to address a register. %r1rd (destination register) (address = 00001) Other fields: In the previous slide, notice that there is an “i” field to distinguish between the two memory formats. Here, i = 1.

Functions + Assembly Assembledcod e. ld: opcode: 11 rd: destination register: 000`1 op3: rs1: i: 1 This is the instruction we just looked at. The right side represents machine code. ld [x], %r These are some other assembled instructions. ld [y], %r addcc %r1,%r2,%r st %r3, [z] jmpl %r15+4, %r

Functions + Assembly Next. We just looked at how to convert Assembly into Machine code. Next: We will briefly look at the steps to convert a high level program into assembly.

Functions + Assembly Summary so far … We looked at –Stages of a compiler (briefly) –Assembly instructions –Translating assembly into machine code … Next: speeding up processing …

Functions + Assembly CPU Performanc e E.g., will a 4.1 Ghz CPU be faster than a 2.0 Ghz CPU? –So is the CPU cycle time a measure of performance? How about amount of cache? Anything else? Next: performance due to pipelining.

Functions + Assembly Pipelining Speeding up the computation process Complex and Reduced Instruction Sets: Complex Instruction Set Computer (CISC) Reduced Instruction Set Computer (RISC) Next: the differences?

Functions + Assembly CISC Vs. RISC A long time back when memory costed –The focus of most computer architects (E.g., Intel and Motorola) Support fewer instructions that performed more complicated computations. E.g., addld [a], [b], [c] would be a complex instruction that replaced: ld [a], %r1 ld [b], %r2 addcc %r1, %r2, %r3 st %r3, [c] Why? Complex instructions  Shorter programs  Smaller memory needed. However, memory became cheaper. So architects started thinking about techniques to use more memory that would speed up computations.

Functions + Assembly Review JVM + Bytecode