1. Compilation Process COP 3402 (Summer 2013)

2. Compilation process Break the command "gcc -o test.c ..." into preprocessing, compilation, assembly, and linking. InputProgramOutput Source code     Preprocessor  Expanded source Expanded code    Compiler        Assembly source Assembly source  Assembler     Object code Object code     Linker        Executable code Executable code  Loader    Execution

3. A simple program that adds two numbers (not including any library). Example1: Source program (call it test.c) int test_fun(int x) {return x + 17;} int main(void) { int x = 1; int y; y = test_fun(x); return 0; } Example

4. Step 1: cpp test.c test.i Output: # 1 "test.c" # 1 "<built-in>" # 1 "<command-line>" # 1 "test.c" int test_fun(int x) {return x + 17;} int main(void) { int x = 1; int y; y = test_fun(x); return 0; } Example: Step 1

5. Step 2: gcc -S test.i -o test.s Output: .file "test.c" .text .globl _test_fun .def _test_fun; .scl 2; .type 32; .endef _test_fun: pushl %ebp movl %esp, %ebp movl 8(%ebp), %eax addl $17, %eax popl %ebp ret .def ___main; .scl 2; .type 32; .endef .globl _main .def _main; .scl 2; .type 32; .endef Example: Step 2

6. Step 2: gcc -S test.i -o test.s Output continued: _main: pushl %ebp movl %esp, %ebp andl $-16, %esp subl $32, %esp call ___main movl $1, 28(%esp) movl 28(%esp), %eax movl %eax, (%esp) call _test_fun movl %eax, 24(%esp) movl $0, %eax leave ret Example: Step 2 Continued

7. Step 3: as test.s -o test.o The file contains the machine code for program test Output (Big Endian; viewed with Notepad++ hex editor plugin): Example: Step 3

8. Step 4: gcc test.o (for linking) and produces a.out a.out is a long file, so it will not be shown here, but you may view it with a hex editor if you follow these steps on your own. Step 5: ./a.out (to load and execute) There will not be any output, but the program should run without error. Example: Steps 4 & 5

9. Step 1: cpp test.c test.i test.i contains the preprocessed c file Step 2: gcc -S test.i -o test.s test.s contains the assembly code Step 3: as test.s -o test.o test.o contains the machine code Step 4: gcc test.o (for linking) and produces a.out a.out is the ELF file Step 5: ./a.out (to load and execute) Compilation Process Summary

10. 1. Follow the steps of the example on your own. Results may vary. 2. Follow the steps of the example with a simple hello world program that includes I/O, and therefore the standard I/O library, stdio.h: #include <stdio.h> Int main (void) {  printf (“Hello, world!\n");  return 0; } Exercises