inst eecs berkeley edu cs61c CS61C Machine Structures Lecture 8 Introduction to MIPS Assembly language Arithmetic 2010 02 05 Hello to Jessy VanDivner listening from Ohio Lecturer SOE Dan Garcia www cs berkeley edu ddgarcia Chinese Hackers The NY Times has an insiders look at the life of a Chinese hacker It s a fascinating peek into the dark side of programming Do hackers work for government military Yes www nytimes com 2010 02 02 business global 02hacker html CS61C L08 Introduction to MIPS Assembly Language Arithmetic 1 Garcia Spring 2010 UCB Review Several techniques for managing heap w malloc free best first next fit slab buddy 2 types of memory fragmentation internal external all suffer from some kind of frag Each technique has strengths and weaknesses none is definitively best Automatic memory management relieves programmer from managing memory All require help from language and compiler Reference Count not for circular structures Mark and Sweep complicated and slow works Copying move active objects back and forth CS61C L08 Introduction to MIPS Assembly Language Arithmetic 2 Garcia Spring 2010 UCB Assembly Language Basic job of a CPU execute lots of instructions Instructions are the primitive operations that the CPU may execute Different CPUs implement different sets of instructions The set of instructions a particular CPU implements is an Instruction Set Architecture ISA Examples Intel 80x86 Pentium 4 IBM Motorola PowerPC Macintosh MIPS Intel IA64 CS61C L08 Introduction to MIPS Assembly Language Arithmetic 3 Garcia Spring 2010 UCB Book Programming From the Ground Up A new book was just released which is based on a new concept teaching computer science through assembly language Linux x86 assembly language to be exact This book teaches how the machine itself operates rather than just the language I ve found that the key difference between mediocre and excellent programmers is whether or not they know assembly language Those that do tend to understand computers themselves at a much deeper level Although almost unheard of today this concept isn t really all that new there used to not be much choice in years past Apple computers came with only BASIC and assembly language and there were books available on assembly language for kids This is why the old timers are often viewed as wizards they had to know assembly language programming slashdot org comment 2004 02 05 CS61C L08 Introduction to MIPS Assembly Language Arithmetic 4 Garcia Spring 2010 UCB Instruction Set Architectures Early trend was to add more and more instructions to new CPUs to do elaborate operations VAX architecture had an instruction to multiply polynomials RISC philosophy Cocke IBM Patterson Hennessy 1980s Reduced Instruction Set Computing Keep the instruction set small and simple makes it easier to build fast hardware Let software do complicated operations by composing simpler ones CS61C L08 Introduction to MIPS Assembly Language Arithmetic 5 Garcia Spring 2010 UCB MIPS Architecture MIPS semiconductor company that built one of the first commercial RISC architectures We will study the MIPS architecture in some detail in this class also used in upper division courses CS 152 162 164 Why MIPS instead of Intel 80x86 MIPS is simple elegant Don t want to get bogged down in gritty details MIPS widely used in embedded apps x86 little used in embedded and more embedded computers than PCs CS61C L08 Introduction to MIPS Assembly Language Arithmetic 6 Garcia Spring 2010 UCB Assembly Variables Registers 1 4 Unlike HLL like C or Java assembly cannot use variables Why not Keep Hardware Simple Assembly Operands are registers limited number of special locations built directly into the hardware operations can only be performed on these Benefit Since registers are directly in hardware they are very fast faster than 1 billionth of a second CS61C L08 Introduction to MIPS Assembly Language Arithmetic 7 Garcia Spring 2010 UCB Assembly Variables Registers 2 4 Drawback Since registers are in hardware there are a predetermined number of them Solution MIPS code must be very carefully put together to efficiently use registers 32 registers in MIPS Why 32 Smaller is faster Each MIPS register is 32 bits wide Groups of 32 bits called a word in MIPS CS61C L08 Introduction to MIPS Assembly Language Arithmetic 8 Garcia Spring 2010 UCB Assembly Variables Registers 3 4 Registers are numbered from 0 to 31 Each register can be referred to by number or name Number references 0 1 2 30 31 CS61C L08 Introduction to MIPS Assembly Language Arithmetic 9 Garcia Spring 2010 UCB Assembly Variables Registers 4 4 By convention each register also has a name to make it easier to code For now 16 23 s0 s7 correspond to C variables 8 15 t0 t7 correspond to temporary variables Later will explain other 16 register names In general use names to make your code more readable CS61C L08 Introduction to MIPS Assembly Language Arithmetic 10 Garcia Spring 2010 UCB C Java variables vs registers In C and most High Level Languages variables declared first and given a type Example int fahr celsius char a b c d e Each variable can ONLY represent a value of the type it was declared as cannot mix and match int and char variables In Assembly Language the registers have no type operation determines how register contents are treated CS61C L08 Introduction to MIPS Assembly Language Arithmetic 11 Garcia Spring 2010 UCB Comments in Assembly Another way to make your code more readable comments Hash is used for MIPS comments anything from hash mark to end of line is a comment and will be ignored This is just like the C99 Note Different from C C comments have format comment so they can span many lines CS61C L08 Introduction to MIPS Assembly Language Arithmetic 12 Garcia Spring 2010 UCB Assembly Instructions In assembly language each statement called an Instruction executes exactly one of a short list of simple commands Unlike in C and most other High Level Languages each line of assembly code contains at most 1 instruction Instructions are related to operations in C or Java Ok enough already gimme my MIPS CS61C L08 Introduction to MIPS Assembly Language Arithmetic 14 Garcia Spring 2010 UCB MIPS Addition and Subtraction 1 4 Syntax of Instructions 1 2 3 4 where 1 operation by name 2 operand getting result destination 3 1st operand for operation source1 4 2nd operand for operation source2 Syntax is rigid 1 operator 3 operands Why Keep Hardware simple via regularity CS61C L08 Introduction to MIPS
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