I have this code:

#include <stdio.h>
int main()
{
printf("a=%d; b=%d; c=%d", 1, 2, 3);
return 0;
};

I compile it with gcc -g 3arg.cpp. Disassemble with objdump -d -M intel a.out. In the output there is exactly one function named _init and it is disassembled like this:

00000000004003e0 <_init>:
  4003e0:       48 83 ec 08             sub    rsp,0x8
  4003e4:       48 8b 05 0d 0c 20 00    mov    rax,QWORD PTR [rip+0x200c0d]        # 600ff8 <_DYNAMIC+0x1d0>
  4003eb:       48 85 c0                test   rax,rax
  4003ee:       74 05                   je     4003f5 <_init+0x15>
  4003f0:       e8 3b 00 00 00          call   400430 <__gmon_start__@plt>
  4003f5:       48 83 c4 08             add    rsp,0x8
  4003f9:       c3                      ret

This is gdb output:

$ gdb -q a.out
Reading symbols from a.out...done.
(gdb) disassemble _init
Dump of assembler code for function _init:
   0x00000000004003e0 <+0>:  sub    $0x8,%rsp
   0x00000000004003e4 <+4>:  mov    0x200c0d(%rip),%rax        # 0x600ff8
   0x00000000004003eb <+11>: test   %rax,%rax
   0x00000000004003ee <+14>: je     0x4003f5 <_init+21>
   0x00000000004003f0 <+16>: callq  0x400430 <__gmon_start__@plt>
   0x00000000004003f5 <+21>: add    $0x8,%rsp
   0x00000000004003f9 <+25>: retq   
End of assembler dump.
(gdb) break _init
Breakpoint 1 at 0x4003e0
(gdb) run
Starting program: [redacted]/a.out 

Breakpoint 1, _init (argc=1, argv=0x7fffffffdf68, envp=0x7fffffffdf78) at ../csu/init-first.c:52
52  ../csu/init-first.c: No such file or directory.
(gdb) disassemble _init
Dump of assembler code for function _init:
=> 0x00007ffff7a36c20 <+0>:  push   %r13
   0x00007ffff7a36c22 <+2>:  push   %r12
   0x00007ffff7a36c24 <+4>:  mov    %edi,%r12d
   0x00007ffff7a36c27 <+7>:  push   %rbp
   0x00007ffff7a36c28 <+8>:  mov    %rsi,%rbp
   0x00007ffff7a36c2b <+11>: push   %rbx
[etc.]

Why is the last disassembly different? It's not even the same data disassembled in a different way. If it's a different _init function:

• how can I put a breakpoint at the one that's seen in the objdump output and the first disassembly in gdb?
• why did gdb say Breakpoint 1 was at 0x4003e0 and then stopped at a different function?