Four stages of compilation process

Pre-processor

We use a high level language such as C++ to write our source code which ends with extensions .c, .cpp, .h etc. The C++ preprocessor removes the comments, copies the contents of the included header files into the source code file, generates macro code, and replaces symbolic constants defined using #define with their values.

gcc -E hello.c -o hello.i 

Compiler

The expanded source code is compiled into the assembly language for the platform. This is the final human readable form.

gcc -Wall -S hello.i -o hello.s 

Assembler

The assembly code is transformed into the object code for the platform.

as hello.s -o hello.o  

Linker

The object code file generated by the assembler is linked together with the object code files for any library functions used to produce an executable file. The extra linking files provide information such as from which address to start the execution, i.e. the entry point

ld -dynamic-linker /lib/ld-linux.so.2/usr/lib/crt1.o /usr/lib/crti.o /usr/lib/gcc-lib/i686/3.3.1/crtbegin.o-L/usr/lib/gcc-lib/i686/3.3.1 hello.o -lgcc -lgcc_eh -lc -lgcc -lgcc_eh/usr/lib/gcc-lib/i686/3.3.1/crtend.o /usr/lib/crtn.o == gcc hello.o