1. Today’s Topic
Breakdown of CC script

2. Today’s 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

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

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

5. C Preprocessor (cpp) Pass over source Define macros
Insert included files
Perform macro substitutions
Define macros
#define NUM
#define xx(v,name,op,metrics) \ v=xxinit(op,name,IR->metrics)
gcc –E example.c sends preprocessor output to stdout

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

7. 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

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

9. 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)

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

11. 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

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

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

14. 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