Program Compilation and Execution

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Program Compilation and Execution

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Todays Topics

• Breakdown of CC script
• Memory Usage during execution

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Todays Objectives

• Within context of compiling C program
• Define actions of linker, compiler, assembler,
  OS, macro preprocessor, loader
• Draw block diagram showing order of linker,
  compiler, assembler, OS, macro preprocessor,
  loader
• Explain why runtime stack needed for C
• Draw logical division of memory into stack, heap
• Compare and contrast stack and heap
• For C program, indicate which variables are
  stored in heap in stack in neither

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Logical Memory Layout
Stack
D Y N A M I C
Currently Not in Use
Not Currently in Use
Heap
Static Space
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Breaking Down CC
Preprocessed Source
source
ASM
Compiler
Assembler
Preprocessor
.s
O B J E C T
Executable Program In Memory
Executable
Linker
Loader
.o
a.out
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Breaking Down CC
Preprocessed Source
source
ASM
Compiler
Assembler
Preprocessor
.s
O B J E C T
Executable Program In Memory
Executable
Linker
Loader
.o
a.out
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C Preprocessor (cpp)

• Pass over source
• Insert included files
• Perform macro substitutions
• Define macros
• define NUM 100
• define xx(v,name,op,metrics) \
  vxxinit(op,name,IR-gtmetrics)
• gcc E example.c sends preprocessor output to
  stdout

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Breaking Down CC
Preprocessed Source
source
ASM
Compiler
Assembler
Preprocessor
.s
O B J E C T
Executable Program In Memory
Executable
Linker
Loader
.o
a.out
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Compiler

• gcc actually name of a script
• Compiler translates one language to another (or
  the same???)
• gcc compiler translates C to assembler
• gcc S example.c saves example.s
• Compiler consists of
• Parser
• Code generation
• Mysticism

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Breaking Down CC
Preprocessed Source
source
ASM
Compiler
Assembler
Preprocessor
.s
O B J E C T
Executable Program In Memory
Executable
Linker
Loader
.o
a.out
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Assembler

• Another translator ??? (as example.s)
• Assembler to (binary) object
• Why not compile straight to binary?
• gcc c example.c to save object
• NM to look at object (nm example.o)

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Breaking Down CC
Preprocessed Source
source
ASM
Compiler
Assembler
Preprocessor
.s
O B J E C T
Executable Program In Memory
Executable
Linker
Loader
.o
a.out
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Linker

• Combine objects, both user .o files and
  libraries, make an executable
• gcc .o lm yields a.out
• gcc o myExec .o lm
• Use nm to look at object

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Breaking Down CC
Preprocessed Source
source
ASM
Compiler
Assembler
Preprocessor
.s
O B J E C T
Executable Program In Memory
Executable
Linker
Loader
.o
a.out
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Loader

• Gets an address to place program
• Changes necessary addresses (if any)
• Places code into memory

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Operating System

• Oversees whole process
• Recognizes gcc example.c command
• Parses flags and arguments
• Invokes gcc script
• Performs memory mangagement (malloc)
• Chooses address to place program

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Dice.c

• int NUM 100000
• main()
• int i, roll, counts
• counts (int) malloc (13 sizeof(int))
• for (i 0 i lt 13 i) countsi 0
• for ( i 0 i lt NUM i)
• roll rand() 6 rand() 6 2
• countsroll
• for (i 2 i lt 13 i)
• printf(There were d rolls of d/n,
• countsi,i)

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Where Are the Variables?
Stack
D Y N A M I C
i roll counts
Currently Not in Use
Not Currently in Use
Space for 13 ints pointed to by counts ?
Heap
Static Space
Code d throws x\n