How GCC compiles a C/C++ program into executable:

• preprocessing Step 1, Source Code (.c, .cpp, .h), Preprocessor (cpp)
• compilation Step 2, Include Header, Expand Macro (.i, .ii) Compiler (gcc, g++)
• assemble Step 3, Assembly Code (.s) Assembler (as) to Machine Code (.o, .obj)
• linking Step 4, Static Library(.lib, .a) Linker (ld)
• execute Step 5, Executable Machine Code (.exe) "./executable"

For example, a gcc main.c -o executable

Filename:

• .c C language file (SourceCode)
• .i Preprocessed C language file
• .s Compiled assembly file
• .o Compiled object file (ObjectCode/ObjectFile/objfile)

GCC Commands:

• -E Preprocessing only
• -S Only preprocess and compile
• -c Only preprocess, compile and assemble
• -o file Specify the generated output file name as file
• -c Create Object File
• -v Display the programs invoked by the compiler.

Key Terms:

• Source Code?
• Object Code?
• Machine Code?
• Binary Code?
• Executable Code?
• Assembly Code?

Catatan tentang objfile dan executable file

Perhatikan bahwa hasil akhir, file foo adalah file yang dapat diekekusi file foo disebut juga {"program biner terkompilasi", "program", "(gabungan) objfile" "executable", "binary", atau hanya "machine code", atau "satu dan nol" (10101010).

*.o adalah obj file pada format obj file, untuk menghasilkan output individu *.o atau objfile digabungkan menjadi satu oleh linker. Linker secara garis besar menggabungkan semua objfile *.o untuk menjadikan executable file, studi kasus disini foo adalah executable file yang merupakan gabungan dari obj file

Notes

Object File can't be read immediately, please disassembly before reading objfile.

Commands to Display assembler

$ objdump -d <objfile.o> // Display assembler contents of executable sections
$ objdump -d <objfile.o> // Display assembler contents of all sections

Source Code .c

main.c

#include <stdio.h>

int funcAdded(int num1, int num2);

int main(){
	int total = funcAdded(5, 3);
	printf("5 + 3 = %d", total);
	
	return 0;
}

add.c

int funcAdded(int num1, int num2) {
	return (num1 + num2);
}

Instant Compilation C/C++ Code

Commands to Compile C Code

$ gcc hello.c -o executable; ./executable
> Output (executable)

Understanding Compilation Process with Linking {main, add}.c to executable!

Step 1

Pre-processing: via the GNU C Preprocessor (cpp.exe), which includes the headers (#include) and expands the macros (#define).

cpp {source.c} > {pre-processor.i}

Create Preprocessed file

$ cpp main.c > main.i
> Output main.i // Output <pre-processor>

Step 2

Compilation: The compiler compiles the pre-processed Source Code into assembly code for a specific processor.

gcc -S pre-processing

Create Assembly file

$ gcc -S main.i
> Output main.s // Output <assembly.s> 

Step 3

Assembly: The assembler (as.exe) converts the assembly code into machine code in the objfile "main.o".

gcc <assembly.s> -o <objfile.o> 

Create Object file

$ as main.s -o main.o
> Output main.o // Output <objfile.o>

Step 4

Create objfile from add.c with default name.

gcc -c <source.c>

Compile Source file .c to Object file .o

$ gcc -c add.c
> Output add.o

Step 5

Linker: links the objfile main.o and add.o to produce an executable file executable.

Linking main.o and add.o to executable

$ gcc main.o add.o -o executable

Step 6

Execute: Show this output from executable file

$ ./executable
> (Output)

Running this Code step-by-step and Check this Output with Terminal

Commands:

cpp main.c > main.i;
ls;
gcc -S main.i;
ls;
as main.s -o main.o;
ls;
gcc -c add.c;
ls;
gcc main.o add.o -o executable;
ls;
./executable;

Output:

➜  c-low-level ls
total 16
-rw-r--r-- 1 kali kali  62 11 Apr   10:59   add.c 
-rw-r--r-- 1 kali kali 143 11 Apr   10:59   main.c 
➜  c-low-level cpp main.c > main.i;
➜  c-low-level ls
total 56
-rw-r--r-- 1 kali kali    62 11 Apr   10:59   add.c 
-rw-r--r-- 1 kali kali   143 11 Apr   10:59   main.c 
-rw-r--r-- 1 kali kali 16398 11 Apr   11:10   main.i 
➜  c-low-level gcc -S main.i;
➜  c-low-level ls
total 64
-rw-r--r-- 1 kali kali    62 11 Apr   10:59   add.c 
-rw-r--r-- 1 kali kali   143 11 Apr   10:59   main.c 
-rw-r--r-- 1 kali kali 16398 11 Apr   11:10   main.i 
-rw-r--r-- 1 kali kali   594 11 Apr   11:10   main.s 
➜  c-low-level as main.s -o main.o;
➜  c-low-level ls
total 72
-rw-r--r-- 1 kali kali    62 11 Apr   10:59   add.c 
-rw-r--r-- 1 kali kali   143 11 Apr   10:59   main.c 
-rw-r--r-- 1 kali kali 16398 11 Apr   11:10   main.i 
-rw-r--r-- 1 kali kali  1632 11 Apr   11:10   main.o 
-rw-r--r-- 1 kali kali   594 11 Apr   11:10   main.s 
➜  c-low-level gcc -c add.c;
➜  c-low-level ls
total 80
-rw-r--r-- 1 kali kali    62 11 Apr   10:59   add.c 
-rw-r--r-- 1 kali kali  1240 11 Apr   11:11   add.o 
-rw-r--r-- 1 kali kali   143 11 Apr   10:59   main.c 
-rw-r--r-- 1 kali kali 16398 11 Apr   11:10   main.i 
-rw-r--r-- 1 kali kali  1632 11 Apr   11:10   main.o 
-rw-r--r-- 1 kali kali   594 11 Apr   11:10   main.s 
➜  c-low-level gcc main.o add.o -o executable;
➜  c-low-level ls
total 120
-rw-r--r-- 1 kali kali    62 11 Apr   10:59   add.c 
-rw-r--r-- 1 kali kali  1240 11 Apr   11:11   add.o 
-rwxr-xr-x 1 kali kali 16672 11 Apr   11:11   executable 
-rw-r--r-- 1 kali kali   143 11 Apr   10:59   main.c 
-rw-r--r-- 1 kali kali 16398 11 Apr   11:10   main.i 
-rw-r--r-- 1 kali kali  1632 11 Apr   11:10   main.o 
-rw-r--r-- 1 kali kali   594 11 Apr   11:10   main.s
➜  c-low-level ./executable; 
5 + 3 = 8
➜  c-low-level objdump -d add.o

add.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <funcAdded>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   89 7d fc                mov    %edi,-0x4(%rbp)
   7:   89 75 f8                mov    %esi,-0x8(%rbp)
   a:   8b 55 fc                mov    -0x4(%rbp),%edx
   d:   8b 45 f8                mov    -0x8(%rbp),%eax
  10:   01 d0                   add    %edx,%eax
  12:   5d                      pop    %rbp
  13:   c3                      retq   
➜  c-low-level objdump -d main.o

main.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <main>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   48 83 ec 10             sub    $0x10,%rsp
   8:   be 03 00 00 00          mov    $0x3,%esi
   d:   bf 05 00 00 00          mov    $0x5,%edi
  12:   e8 00 00 00 00          callq  17 <main+0x17>
  17:   89 45 fc                mov    %eax,-0x4(%rbp)
  1a:   8b 45 fc                mov    -0x4(%rbp),%eax
  1d:   89 c6                   mov    %eax,%esi
  1f:   48 8d 3d 00 00 00 00    lea    0x0(%rip),%rdi        # 26 <main+0x26>
  26:   b8 00 00 00 00          mov    $0x0,%eax
  2b:   e8 00 00 00 00          callq  30 <main+0x30>
  30:   b8 00 00 00 00          mov    $0x0,%eax
  35:   c9                      leaveq 
  36:   c3                      retq 

References

• GCC and Make: Compiling, Linking and Building C/C++ Applications - www3.ntu.edu.sg
• Solve the mystery of the three lives and three generations of HelloWorld through the ELF file of Linux (from now on, your youth will not be lost) - programmersought
• Preprocessed .i file - pvs-studio
• 4.3 Preprocessing source files - linuxtopia
• Introduction to the ELF Format Part II : Understanding Program Headers - k3170makan