program runs even if section is not executable

My main section is defined as section .code write

I deliberately removed the exec parameter, and noticed that, after assembling and linking, the program runs fine.

objdump -d myprogram is empty. And gdb cannot debug it : break _start says "Function _start not defined", but info variables shows _start.

But the program still runs. How's that possible ?

Architecture is intel 32-bit, on linux (ubuntu 12).

The probram is doing an execve syscall, opening a /bin/sh shell.

The nasm program :

global _start

section .code write

_start:
        jmp short call_shellcode

shellcode:
        pop esi

        xor ebx, ebx
        mov byte [esi +7], bl
        mov dword [esi +8], esi
        mov dword [esi +12], ebx

        lea ebx, [esi]
        lea ecx, [esi +8]
        lea edx, [esi +12]

        xor eax, eax
        mov al, 0xb
        int 0x80

call_shellcode:
        call shellcode
        message db "/bin/shABBBBCCCC"