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CSCI-365 Computer Organization Lecture Note: Some slides and/or pictures in the following are adapted from: Computer Organization and Design, Patterson.

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Presentation on theme: "CSCI-365 Computer Organization Lecture Note: Some slides and/or pictures in the following are adapted from: Computer Organization and Design, Patterson."— Presentation transcript:

1 CSCI-365 Computer Organization Lecture Note: Some slides and/or pictures in the following are adapted from: Computer Organization and Design, Patterson & Hennessy, ©2005 Some slides and/or pictures in the following are adapted from: slides ©2008 UCB 8

2 The 20 MIPS Instructions Covered So Far InstructionUsage Load upper immediate lui rt,imm Add add rd,rs,rt Subtract sub rd,rs,rt Set less than slt rd,rs,rt Add immediate addi rt,rs,imm Set less than immediate slti rd,rs,imm AND and rd,rs,rt OR or rd,rs,rt XOR xor rd,rs,rt NOR nor rd,rs,rt AND immediate andi rt,rs,imm OR immediate ori rt,rs,imm XOR immediate xori rt,rs,imm Load word lw rt,imm(rs) Store word sw rt,imm(rs) Jump j L Jump register jr rs Branch less than 0 bltz rs,L Branch equal beq rs,rt,L Branch not equal bne rs,rt,L Copy Control transfer Logic Arithmetic Memory access op fn

3 Interpretation vs. Translation How do we run a program written in a source language? Interpreter: Directly executes a program in the source language. Examples? Translator: Converts a program from the source language to an equivalent language in another language

4 Interpretation vs. Translation Generally easier to write interpreter Interpreter closer to high-level, so can give better error messages (e.g., SPIM) Interpreter slower (10x?) but code is smaller (1.5x to 2x?) Interpreter provides instruction set independence: run on any machine –Assuming interpreter written in a portable format

5 Interpretation vs. Translation Translated/compiled code almost always more efficient and therefore higher performance –Important for many applications, particularly operating systems Translation/compilation helps “hide” the program “source” from the users –One model for creating value in the marketplace (e.g., Microsoft keeps all their source code secret) –Alternative model, “open source”, creates value by publishing the source code and fostering a community of developers (e.g., Linux)

6 C program: foo.c Compiler Assembly program: foo.s Assembler Linker Executable(mach lang pgm): a.out Loader Memory Object(mach lang module): foo.o lib.o Steps to Starting a Program (translation)

7 Input: High-Level Language Code (e.g., C, Java such as foo.c ) Output: Assembly Language Code (e.g., foo.s for MIPS) Note: Output may contain pseudoinstructions Pseudoinstructions: instructions that assembler understands but not in machine. For example: – mov $s1,$s2  or $s1,$s2,$zero Compiler

8 MIPS Pseudo- instructions PseudoinstructionUsage Move move regd,regs Load address la regd,address Load immediate li regd,anyimm Absolute value abs regd,regs Negate neg regd,regs Multiply (into register) mul regd,reg1,reg2 Divide (into register) div regd,reg1,reg2 Remainder rem regd,reg1,reg2 Set greater than sgt regd,reg1,reg2 Set less or equal sle regd,reg1,reg2 Set greater or equal sge regd,reg1,reg2 Rotate left rol regd,reg1,reg2 Rotate right ror regd,reg1,reg2 NOT not reg Load doubleword ld regd,address Store doubleword sd regd,address Branch less than blt reg1,reg2,L Branch greater than bgt reg1,reg2,L Branch less or equal ble reg1,reg2,L Branch greater or equal bge reg1,reg2,L Copy Control transfer Shift Arithmetic Memory access Logic

9 C program: foo.c Compiler Assembly program: foo.s Assembler Linker Executable(mach lang pgm): a.out Loader Memory Object(mach lang module): foo.o lib.o Where Are We Now? Compiler writing course

10 Input: Assembly Language Code (e.g., foo.s for MIPS) Output: Object Code, information tables (e.g., foo.o for MIPS) Reads and Uses Directives Replace Pseudoinstructions Allow programmers to associate arbitrary names (labels or symbols) with memory locations Produce Machine Language Creates Object File Assembler

11 Give directions to assembler, but do not produce machine instructions.text : Subsequent items put in user text segment (machine code).data : Subsequent items put in user data segment (binary rep of data in source file).globl sym : declares sym global and can be referenced from other files.asciiz str : Store the string str in memory and null-terminate it.word w1…wn : Store the n 32-bit quantities in successive memory words Assembler Directives (p. A-51 to A-53)

12 Pseudoinstructions Example of one-to-one pseudoinstruction: The following not $s0 # complement ($s0) is converted to the real instruction: nor $s0,$s0,$zero # complement ($s0) Example of one-to-several pseudoinstruction: The following abs $t0,$s0 # put |($s0)| into $t0 is converted to the sequence of real instructions: add $t0,$s0,$zero # copy x into $t0 slt $at,$t0,$zero # is x negative? beq $at,$zero,+4 # if not, skip next instr sub $t0,$zero,$s0 # the result is 0 – x

13 Assembler treats convenient variations of machine language instructions as if real instructions Pseudo:Real: subu $sp,$sp,32addiu $sp,$sp,-32 sd $a0, 32($sp) sw $a0, 32($sp) sw $a1, 36($sp) mul $t7,$t6,$t5mul $t6,$t5 mflo $t7 addu $t0,$t6,1addiu $t0,$t6,1 ble $t0,100,loopslti $at,$t0,101 bne $at,$0,loop la $a0, strlui $at,l.str ori $a0,$at,r.str Pseudoinstruction Replacement

14 Example: C  Asm  Obj  Exe  Run #include int main (int argc, char *argv[]) { int i, sum = 0; for (i = 0; i <= 100; i++) sum = sum + i * i; printf ("The sum from is %d\n", sum); } prog.c printf lives in libc

15 Compilation: MIPS. text.align2.globlmain main: subu $sp,$sp,16 sw$ra,4($sp) sd$a0, 16($sp) sw$0, 8($sp) sw$0, 12($sp) loop: lw$t6, 12($sp) mul$t7, $t6,$t6 lw$t8, 8($sp) addu $t9,$t8,$t7 sw$t9, 8($sp) addu $t0, $t6, 1 sw$t0, 12($sp) ble$t0,100, loop la$a0, str lw$a1, 8($sp) jal printf move $v0, $0 lw$ra, 4($sp) addiu $sp,$sp,16 jr $ra.data.align0 str:.asciiz"The sum from is %d\n" Where are 7 pseudo- instructions?

16 Compilation: MIPS.text.align2.globlmain main: subu $sp,$sp,16 sw$ra, 4($sp) sd$a0, 16($sp) sw$0, 8($sp) sw$0, 12($sp) loop: lw$t6, 12($sp) mul$t7, $t6,$t6 lw$t8, 8($sp) addu $t9,$t8,$t7 sw$t9, 8($sp) addu $t0, $t6, 1 sw$t0, 12($sp) ble$t0,100, loop la$a0, str lw$a1, 8($sp) jal printf move $v0, $0 lw$ra, 4($sp) addiu $sp,$sp,16 jr $ra.data.align0 str:.asciiz"The sum from is %d\n" 7 pseudo-instructions underlined

17 Assembly step 1 00 addiu $29,$29, sw$31,4($29) 08 sw$4, 16($29) 0c sw$5, 20($29) 10 sw $0, 8($29) 14 sw $0, 12($29) 18 lw $14, 12($29) 1c multu $14, $14 20 mflo $15 24 lw $24, 8($29) 28 addu $25,$24,$15 2c sw $25, 8($29) 30 addiu $8,$14, 1 34 sw$8,12($29) 38 slti$1,$8, 101 3c bne$1,$0, loop 40 lui$4, l.str 44 ori$4,$4,r.str 48 lw$5,8($29) 4c jalprintf 50 add$2, $0, $0 54 lw $31,4($29) 58 addiu $29,$29,16 5c jr $31 Remove pseudoinstructions, assign addresses

18 Simple Case –Arithmetic, Logical, Shifts, and so on –All necessary info is within the instruction already What about Branches? –PC-Relative –So once pseudo-instructions are replaced by real ones, we know by how many instructions to branch So these can be handled Producing Machine Language

19 “Forward Reference” problem –Branch instructions can refer to labels that are “forward” in the program: or $v0,$0,$0 L1:slt $t0,$0,$a1 beq $t0,$0,L2 addi $a1,$a1,-1 j L1 L2:add $t1,$a0,$a1 –Solved by taking 2 passes over the program First pass remembers position of labels Second pass uses label positions to generate code

20 What about jumps ( j and jal )? –Jumps require absolute address –So, forward or not, still can’t generate machine instruction without knowing the position of instructions in memory What about references to data? – la gets broken up into lui and ori –These will require the full 32-bit address of the data These can’t be determined yet, so we create two tables… Producing Machine Language

21 List of “items” in this file that may be used by other files What are they? –Labels: function calling –Data: anything in the global part of the.data section; variables which may be accessed across files Symbol Table

22 List of “items” for which this file needs the address What are they? –Any label jumped to: j or jal internal external (including lib files) –Any data label reference such as the la instruction Relocation Table

23 Assembly step 2 Create relocation table and symbol table Symbol Table –Label Address (in module) Type main:0x global text loop:0x local text str:0x local data Relocation Information –AddressInstr. TypeDependency 0x luil.str 0x orir.str 0x cjalprintf

24 Assembly step 3 00 addiu $29,$29, sw$31,4($29) 08 sw$4, 16($29) 0c sw$5, 20($29) 10 sw $0, 8($29) 14 sw $0, 12($29) 18 lw $14, 12($29) 1c multu $14, $14 20 mflo $15 24 lw $24, 8($29) 28 addu $25,$24,$15 2c sw $25, 8($29) 30 addiu $8,$14, 1 34 sw$8,12($29) 38 slti$1,$8, 101 3c bne$1,$0, lui$4, l.str 44 ori$4,$4,r.str 48 lw $5,8($29) 4c jal printf 50 add $2, $0, $0 54 lw $31,4($29) 58 addiu $29,$29,16 5c jr $31 Resolve local PC-relative labels

25 Assembly step 4 Generate object (.o) file –Output binary representation for text segment (instructions) data segment (data) symbol and relocation tables –Using dummy “placeholders” or “guesses” for unresolved absolute and external references

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28 object file header: size and position of the other pieces of the object file text segment: the machine code data segment: binary representation of the data in the source file relocation information: identifies lines of code that need to be “handled” symbol table: list of this file’s labels and data that can be referenced debugging information A standard format is ELF (except MS) Object File Format

29 C program: foo.c Compiler Assembly program: foo.s Assembler Linker Executable(mach lang pgm): a.out Loader Memory Object(mach lang module): foo.o lib.o Where Are We Now?

30 Input: Object Code files (e.g., foo.o,libc.o for MIPS) Output: Executable Code (e.g., a.out for MIPS) Combines several object (.o) files into a single executable (“linking”) Enable Separate Compilation of files –Changes to one file do not require recompilation of whole program Windows NT source is > 40 M lines of code! –Old name “Link Editor” from editing the “links” in jump and link instructions Linker

31 FIGURE B.3.1 The linker searches a collection of object fi les and program libraries to find nonlocal routines used in a program, combines them into a single executable file, and resolves references between routines in different files. Copyright © 2009 Elsevier, Inc. All rights reserved.

32 .o file 1 text 1 data 1 info 1.o file 2 text 2 data 2 info 2 Linker a.out Relocated text 1 Relocated text 2 Relocated data 1 Relocated data 2 Linker

33 Step 1: Take text segment from each.o file and put them together Step 2: Take data segment from each.o file, put them together, and concatenate this onto end of text segments Step 3: Resolve References –Go through Relocation Table and handle each entry –That is, fill in all absolute addresses Linker

34 Linker assumes first word of first text segment is at address 0x (More on this later when we study “virtual memory”) Linker knows: –length of each text and data segment –ordering of text and data segments Linker calculates: –absolute address of each label to be jumped to (internal or external) and each piece of data being referenced Resolving References

35 To resolve references: –Based on list in each relocation table search for reference (label) in all “user” symbol tables –if not found, search library files (for example, for printf ) –once absolute address is determined, fill in the machine code appropriately Output of linker: executable file containing text and data (plus header) Resolving References

36 FIGURE 2.13 The MIPS memory allocation for program and data. These addresses are only a software convention, and not part of the MIPS architecture. The stack pointer is initialized to 7fff fffc hex and grows down toward the data segment. At the other end, the program code (“text”) starts at hex. The static data starts at hex. Dynamic data, allocated by malloc in C and by new in Java, is next. It grows up toward the stack in an area called the heap. The global pointer, $gp, is set to an address to make it easy to access data. It is initialized to hex so that it can access from hex to 1000 ffff hex using the positive and negative 16-bit offsets from $gp. This information is also found in Column 4 of the MIPS Reference Data Card at the front of this book. Copyright © 2009 Elsevier, Inc. All rights reserved.

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39 Problem Link the object files above to form the executable file header. Assume that Procedure A has a text size of 0x140 and data size of 0x40 and Procedure B has a text size of 0x300 and data size of 0x50.

40 Text Size???? Data Size????? TextAddressInstruction ???????lbu $a0, ????($gp) ?????????jal ????? …… ??????????sw $a1, ????($gp) ??????????jal ?????????? …… Data???????????(X) …… ???????????(Y)

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42 Static vs. Dynamically linked libraries What we’ve described is the traditional way: “statically- linked” approach –The library is now part of the executable, so if the library updates we don’t get the fix (have to recompile if we have source) –It includes the entire library even if not all of it will be used –Executable is self-contained An alternative is dynamically linked libraries (DLL), common on Windows & UNIX platforms –1 st run overhead for dynamic linker-loader –Having executable isn’t enough anymore!

43 C program: foo.c Compiler Assembly program: foo.s Assembler Linker Executable(mach lang pgm): a.out Loader Memory Object(mach lang module): foo.o lib.o Where Are We Now?

44 Input: Executable Code (e.g., a.out for MIPS) Output: (program is run) Executable files are stored on disk When one is run, loader’s job is to load it into memory and start it running In reality, loader is the operating system (OS) –loading is one of the OS tasks Loader


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