Pengantar Organisasi Komputer

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IKI10230Pengantar Organisasi KomputerKuliah no.
09 Compiling-Assembling-Linking
Sumber1. Paul Carter, PC Assembly Language2.
Hamacher. Computer Organization, ed-53. Materi
kuliah CS61C/2000 CS152/1997, UCB
21 April 2004 L. Yohanes Stefanus
(yohanes_at_cs.ui.ac.id)Bobby Nazief
(nazief_at_cs.ui.ac.id) bahan kuliah
http//www.cs.ui.ac.id/kuliah/POK/
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Steps to Starting a Program

• C program foo.c

Compiler
Assembly program foo.s
Assembler
Object(mach lang module) foo.o
Linker
Executable(mach lang pgm) foo.exe
Loader
Memory
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Example C ? Asm ? Obj ? Exe ? Run

• include ltstdio.hgt
• int main (int argc, char argv)
• int i
• int sum 0
• for (i 0 i lt 100 i i 1)
• sum sum i i
• printf ("The sum from 0 .. 100 is d\n", sum)

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Compiler

• Input High-Level Language Code (e.g., C, Java)
• Output Assembly Language Code(e.g., Intel x86)
• Note Output may contain directives
  pseudoinstructions

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Example C ? Asm ? Obj ? Exe ? Run

• segment .text
• LC0 db "The sum from 0 .. 100 is d",0xa,0
• _main
• push ebp
• mov ebp,esp
• sub esp,24
• mov dword ebp-8,0
• mov dword ebp-4,0
• L3
• cmp dword ebp-4,100
• jle L6
• jmp L4
• L6
• mov eax,ebp-4
• imul eax,ebp-4
• add ebp-8,eax

L5 inc dword ebp-4 jmp L3 L4
add esp,-8 mov eax,ebp-8
push eax push dword LC0 call
_printf add esp,16 L2 mov
esp,ebp pop ebp ret
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Where Are We Now?

• C program foo.c

Compiler
Assembly program foo.s
Assembler
Object(mach lang module) foo.o
Linker
Executable(mach lang pgm) a.out
Loader
Memory
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Assembler

• Reads and Uses Directives
• Replace Pseudoinstructions
• Produce Machine Language
• Creates Object File

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Producing Machine Language

• Simple Case
• Arithmetic, Logical, Shifts, and so on.
• All necessary info is within the instruction
  already.
• What about Branches?
• PC-Relative
• So once pseudoinstructions are replaced by real
  ones, we know by how many instructions to branch.
• What about jumps?
• Some require absolute address.
• What about references to data?
• These will require the full 32-bit address of the
  data.
• Addresses cant be determined yet, so we create
  two tables

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Symbol Table

• List of items in this file that may be used by
  other files.
• What are they?
• Labels function calling
• Data anything in the .data section variables
  which may be accessed across files
• First Pass record label-address pairs
• Second Pass produce machine code
• Result can jump to a later label without first
  declaring it

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Relocation Table

• List of items for which this file needs the
  address.
• What are they?
• Any label jumped to jmp or call
• internal
• external (including lib files)
• Any piece of data

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Object File Format

• 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 files labels and data
  that can be referenced
• debugging information

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Example C ? Asm ? Obj ? Exe ? Run

• segment .text
• 0x0
• db "The sum from 0 .. 100 is d",0xa,0
• 0x1d
• push ebp
• mov ebp,esp
• sub esp,24
• mov dword ebp-8,0
• mov dword ebp-4,0
• 0x34
• cmp dword ebp-4,100
• jle 0x05 (0x42)
• jmp 0x00000012 (0x54)
• 0x42
• mov eax,ebp-4
• imul eax,ebp-4
• add ebp-8,eax

0x4c inc dword ebp-4 jmp
0xffffffe0 (0x34) 0x54 add esp,-8
mov eax,ebp-8 push eax push
0x0 call 0x0 add esp,16 0x6e
mov esp,ebp pop ebp ret
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Symbol Table Entries

• Symbol Table
• Label Address
• LC0 0x00000000
• main 0x0000001d
• L3 0x00000034
• L6 0x00000042
• L5 0x0000004c
• L4 0x00000054
• L2 0x0000006e
• Relocation Information
• Offset Type Value
• 0x0000005f dir32 .text
• (LC0 offset 0 of .text segment)
• 0x00000064 DISP32 _printf

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Where Are We Now?

• C program foo.c

Compiler
Assembly program foo.s
Assembler
Object(mach lang module) foo.o
Linker
Executable(mach lang pgm) a.out
Loader
Memory
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Link Editor/Linker

• 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

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Four Types of Addresses

• PC-Relative Addressing (beq, bne) never relocate
• Absolute Address (jmp, call) always relocate
• External Reference (usually call) always
  relocate
• Data Reference always relocate

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Resolving References

• Linker assumes first word of first text segment
  is at address 0x00000000.
• 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
• To resolve references
• search for reference (data or label) in all
  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)

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Example C ? Asm ? Obj ? Exe ? Run

• segment .text
• 0x15c0
• db "The sum from 0 .. 100 is d",0xa,0
• 0x15dd
• push ebp
• mov ebp,esp
• sub esp,24
• mov dword ebp-8,0
• mov dword ebp-4,0
• 0x15f4
• cmp dword ebp-4,100
• jle 0x05 (0x1602)
• jmp 0x12 (0x1614)
• 0x1602
• mov eax,ebp-4
• imul eax,ebp-4
• add ebp-8,eax

0x160c inc dword ebp-4 jmp 0xe0
(0x15f4) 0x1614 add esp,-8 mov
eax,ebp-8 push eax push
0x000015c0 call 0x00001778 (0x2da0)
add esp,16 0x162e mov esp,ebp
pop ebp ret 0x1628 0x1778 0x2da0
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Peta Memori .EXE

• 00000000
• ...
• 000015C0
• 00001631
• ...
• 0000B000
• ...
• 0000BB04

Obj lainnya
Foo.o
.text
Obj lainnya (..., _printf, ...)
.data
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Where Are We Now?

• C program foo.c

Compiler
Assembly program foo.s
Assembler
Object(mach lang module) foo.o
Linker
Executable(mach lang pgm) a.out
Loader
Memory
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Loader (1/3)

• Executable files are stored on disk.
• When one is run, loaders 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

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Loader (2/3)

• So what does a loader do?
• Reads executable files header to determine size
  of text and data segments
• Creates new address space for program large
  enough to hold text and data segments, along with
  a stack segment
• Copies instructions and data from executable file
  into the new address space (this may be anywhere
  in memory)

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Loader (3/3)

• Copies arguments passed to the program onto the
  stack
• Initializes machine registers
• Most registers cleared, but stack pointer
  assigned address of 1st free stack location
• Jumps to start-up routine that copies programs
  arguments from stack to registers and sets the PC
• If main routine returns, start-up routine
  terminates program with the exit system call

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Example C ? Asm ? Obj ? Exe ? Run

• 0x000015c0 0x20656854 0x206d7573 0x6d6f7266 0x2e2
  03020
• 0x000015d0 0x3031202e 0x73692030 0x0a642520 0xe58
  95500
• 0x000015e0 0x0018ec81 0x45c70000 0x000000f8 0xfc4
  5c700
• 0x000015f0 0x00000000 0x64fc7d81 0x7e000000 0x001
  2e905
• 0x00001600 0x458b0000 0x45af0ffc 0xf84501fc 0xe9f
  c45ff
• 0x00001610 0xffffffe0 0xfff8c481 0x458bffff 0xc06
  850f8
• 0x00001620 0xe8000015 0x00001778 0x0010c481 0xec8
  90000
• 0x00001630 0x0000c35d
• 0x000015c0 54 68 65 20 73 75 62 20 66 72 6f 6d
  20 30 20 2e
• T h e s u m f r o m
  0 .
• 000015dd 55 push ebp
• 000015de 89e5 mov ebp,esp
• 000015e0 81ec18000000 sub esp,0x18
• 000015e6 c745f800000000 mov ebp-8,0
• 000015ed c745fc00000000 mov ebp-4,0
• 000015f4 817dfc64000000 cmp ebp-4,0x64
• 000015fb 7e05 jle 0x1602

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• .ASM, .O, .EXE
• (FORMAT COFF)

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Example C ? Asm ? Obj ? Exe ? Run

• .text
• LC0
• .ascii "The sum from 0 .. 100 is d\12\0"
• main
• pushl ebp
• movl esp,ebp
• subl 24,esp
• movl 0,-8(ebp)
• movl 0,-4(ebp)
• L3
• cmpl 100,-4(ebp)
• jle L6
• jmp L4

L6 movl -4(ebp),eax imull
-4(ebp),eax addl eax,-8(ebp) L5
incl -4(ebp) jmp L3 L4 addl
-8,esp movl -8(ebp),eax pushl
eax pushl LC0 call _printf
addl 16,esp L2 movl ebp,esp
popl ebp ret
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Example C ? Asm ? Obj ? Exe ? Run
0x40 movl -4(ebp),eax imull
-4(ebp),eax addl eax,-8(ebp) 0x4a
incl -4(ebp) jmp -0x1b
(0x34) 0x50 addl -8,esp movl
-8(ebp),eax pushl eax pushl
0x0 call 0x0 (undefined) addl
16,esp 0x64 movl ebp,esp
popl ebp ret

• .text
• 0x0
• .ascii "The sum from 0 .. 100 is d\12\0"
• 0x20
• pushl ebp
• movl esp,ebp
• subl 24,esp
• movl 0,-8(ebp)
• movl 0,-4(ebp)
• 0x34
• cmpl 100,-4(ebp)
• jle 6 (0x40)
• jmp 0x14 (0x50)

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Symbol Table Entries

• Symbol Table
• Label Address
• LC0 0x00000000
• L2 0x00000064
• L3 0x00000034
• L4 0x00000050
• L5 0x0000004a
• L6 0x00000040
• main 0x00000020
• Relocation Information
• Address Instr. Type Dependency
• 0x0000005c call printf

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Example C ? Asm ? Obj ? Exe ? Run
0x1600 movl -4(ebp),eax imull
-4(ebp),eax addl eax,-8(ebp) 0x160a
incl -4(ebp) jmp -0x1b
(0x15f4) 0x1610 addl -8,esp
movl -8(ebp),eax pushl eax
pushl 0x15c0 call 0x2d90 addl
16,esp 0x1624 movl ebp,esp
popl ebp ret

• .text
• 0x15c0
• .ascii "The sum from 0 .. 100 is d\12\0"
• 0x15e0
• pushl ebp
• movl esp,ebp
• subl 24,esp
• movl 0,-8(ebp)
• movl 0,-4(ebp)
• 0x15f4
• cmpl 100,-4(ebp)
• jle 6 (0x1600)
• jmp 0x14 (0x1610)