Strange behavior in AMD64 Instruction pointer - c

Question

I was reading Hacking: The Art of Exploitation by Jon Erickson, and followed the example in the book in my Kali Linux system (64 bit).
I wrote a simple C program:
#include<stdio.h>
int main()
{
int i;
for(i=0;i<10;i++)
{
printf("Hello");
}
}
After using objdump and gdb to examine the executable, I found something strange.
As the picture shows, the main function was in the "0x000000000000063a".
But the breakpoint info after the gdb "run" command, it seems that the program stopped at 63e rather than 63a.
Another peculiar thing is that the value in the instruction pointer (rip) was 0x55555555463e.
Shouldn't it be 0x000000000000063a?
Where do those 5s come from?

Answer 1

GDB sets breakpoints on useful code for a function if you don't set an asterisk. It omits all preparation for a function(prologue). To make it clear try to debug the following code:
#include <stdio.h>
int main()
{
int i=10;
i++;
return 0;
}
Gdb session:
(gdb) b main
Breakpoint 1 at 0x80483e1
(gdb) b *main
Breakpoint 2 at 0x80483db
(gdb) r
Starting program: /home/src/main
Breakpoint 2, 0x080483db in main ()
(gdb) disas
Dump of assembler code for function main:
=> 0x080483db <+0>: push ebp
0x080483dc <+1>: mov ebp,esp
0x080483de <+3>: sub esp,0x10
0x080483e1 <+6>: mov DWORD PTR [ebp-0x4],0xa
0x080483e8 <+13>: add DWORD PTR [ebp-0x4],0x1
0x080483ec <+17>: mov eax,0x0
0x080483f1 <+22>: leave
0x080483f2 <+23>: ret
End of assembler dump.
(gdb) c
Continuing.
Breakpoint 1, 0x080483e1 in main ()
(gdb) disas
Dump of assembler code for function main:
0x080483db <+0>: push ebp
0x080483dc <+1>: mov ebp,esp
0x080483de <+3>: sub esp,0x10
=> 0x080483e1 <+6>: mov DWORD PTR [ebp-0x4],0xa
0x080483e8 <+13>: add DWORD PTR [ebp-0x4],0x1
0x080483ec <+17>: mov eax,0x0
0x080483f1 <+22>: leave
0x080483f2 <+23>: ret
End of assembler dump.
in this case, preparation to execute useful code of the function is :
0x080483db <+0>: push ebp
0x080483dc <+1>: mov ebp,esp
0x080483de <+3>: sub esp,0x10
first instruction in main:
int i=10;
compiled into:
mov DWORD PTR [ebp-0x4],0xa
GDB set a breakpoint on the instruction, when we give the command b main
But if we use the command with an asterisk(pointer) b *main we set a breakpoint on the actual address of the function(on first instruction of prologue).
In OP case, if we set breakpoint by break *main and then run, the instruction pointer register(rip) will have the value 0x55555555463a