Easy bypass for ptrace(PTRACE_TRACEME, 0, 0) in GDB)

Start GDB and execute the following commands:

catch syscall ptrace
commands 1
set ($eax) = 0
continue
end

Then, run the app and voilá! you can debug your program :)

Example: 
{{{
zulma@palermo:~$ gdb ./Downloads/zwiebel 
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...

warning: ~/.gdbinit.local: No such file or directory
Reading symbols from ./Downloads/zwiebel...(no debugging symbols found)...done.
gdb$ b main
Breakpoint 1 at 0x400800
gdb$ r
Starting program: /home/zulma/Downloads/zwiebel 
:(
[Inferior 1 (process 10646) exited with code 0377]
-----------------------------------------------------------------------------------------------------------------------[regs]
  RAX:Error while running hook_stop:
No registers.
gdb$ 
}}}

The program executed normally and didn't stop in the breakpoint at main.

Now, the glory commands:

{{{
zulma@palermo:~$ gdb ./Downloads/zwiebel 
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...

warning: ~/.gdbinit.local: No such file or directory
Reading symbols from ./Downloads/zwiebel...(no debugging symbols found)...done.
gdb$ catch syscall ptrace
Catchpoint 1 (syscall 'ptrace' [101])
gdb$ commands 1
Type commands for breakpoint(s) 1, one per line.
End with a line saying just "end".
>set ($rax) = 0
>continue 
>end
gdb$ b main
Breakpoint 2 at 0x400800
gdb$ r
Starting program: /home/zulma/Downloads/zwiebel 
-----------------------------------------------------------------------------------------------------------------------[regs]
  RAX: 0xFFFFFFFFFFFFFFDA  RBX: 0x0000000000000001  RBP: 0x0000000000000002  RSP: 0x00007FFFFFFFDD78  o d I t S z a p c 
  RDI: 0x0000000000000000  RSI: 0x0000000000000000  RDX: 0x0000000000000000  RCX: 0xFFFFFFFFFFFFFFFF  RIP: 0x00007FFFF7B073EE
  R8 : 0x00000000FFFFFFFF  R9 : 0x00007FFFF7DEA530  R10: 0x0000000000000000  R11: 0x0000000000000282  R12: 0x0000000000601000
  R13: 0x00007FFFFFFFDEB8  R14: 0x00007FFFFFFFDEA8  R15: 0x0000000000000001
  CS: 0033  DS: 0000  ES: 0000  FS: 0000  GS: 0000  SS: 002B				
-----------------------------------------------------------------------------------------------------------------------[code]
=> 0x7ffff7b073ee <ptrace+78>:	cmp    rax,0xfffffffffffff000
   0x7ffff7b073f4 <ptrace+84>:	ja     0x7ffff7b07416 <ptrace+118>
   0x7ffff7b073f6 <ptrace+86>:	test   rax,rax
   0x7ffff7b073f9 <ptrace+89>:	js     0x7ffff7b07414 <ptrace+116>
   0x7ffff7b073fb <ptrace+91>:	cmp    r8d,0x2
   0x7ffff7b073ff <ptrace+95>:	ja     0x7ffff7b07414 <ptrace+116>
   0x7ffff7b07401 <ptrace+97>:	mov    rax,QWORD PTR [rip+0x2cba60]        # 0x7ffff7dd2e68
   0x7ffff7b07408 <ptrace+104>:	mov    DWORD PTR fs:[rax],0x0
-----------------------------------------------------------------------------------------------------------------------------

Catchpoint 1 (call to syscall ptrace), 0x00007ffff7b073ee in ptrace (request=PTRACE_TRACEME) at ../sysdeps/unix/sysv/linux/ptrace.c:45
45	../sysdeps/unix/sysv/linux/ptrace.c: No such file or directory.
-----------------------------------------------------------------------------------------------------------------------[regs]
  RAX: 0xFFFFFFFFFFFFFFFF  RBX: 0x0000000000000001  RBP: 0x0000000000000002  RSP: 0x00007FFFFFFFDD78  o d I t S z a p c 
  RDI: 0x0000000000000000  RSI: 0x0000000000000000  RDX: 0x0000000000000000  RCX: 0xFFFFFFFFFFFFFFFF  RIP: 0x00007FFFF7B073EE
  R8 : 0x00000000FFFFFFFF  R9 : 0x00007FFFF7DEA530  R10: 0x0000000000000000  R11: 0x0000000000000282  R12: 0x0000000000601000
  R13: 0x00007FFFFFFFDEB8  R14: 0x00007FFFFFFFDEA8  R15: 0x0000000000000001
  CS: 0033  DS: 0000  ES: 0000  FS: 0000  GS: 0000  SS: 002B				
-----------------------------------------------------------------------------------------------------------------------[code]
=> 0x7ffff7b073ee <ptrace+78>:	cmp    rax,0xfffffffffffff000
   0x7ffff7b073f4 <ptrace+84>:	ja     0x7ffff7b07416 <ptrace+118>
   0x7ffff7b073f6 <ptrace+86>:	test   rax,rax
   0x7ffff7b073f9 <ptrace+89>:	js     0x7ffff7b07414 <ptrace+116>
   0x7ffff7b073fb <ptrace+91>:	cmp    r8d,0x2
   0x7ffff7b073ff <ptrace+95>:	ja     0x7ffff7b07414 <ptrace+116>
   0x7ffff7b07401 <ptrace+97>:	mov    rax,QWORD PTR [rip+0x2cba60]        # 0x7ffff7dd2e68
   0x7ffff7b07408 <ptrace+104>:	mov    DWORD PTR fs:[rax],0x0
-----------------------------------------------------------------------------------------------------------------------------

Catchpoint 1 (returned from syscall ptrace), 0x00007ffff7b073ee in ptrace (request=PTRACE_TRACEME) at ../sysdeps/unix/sysv/linux/ptrace.c:45
45	in ../sysdeps/unix/sysv/linux/ptrace.c
-----------------------------------------------------------------------------------------------------------------------[regs]
  RAX: 0x0000000000400800  RBX: 0x0000000000000000  RBP: 0x0000000000000000  RSP: 0x00007FFFFFFFDDC8  o d I t s Z a P c 
  RDI: 0x0000000000000001  RSI: 0x00007FFFFFFFDEA8  RDX: 0x00007FFFFFFFDEB8  RCX: 0xFFFFFFFFFFFFFFFF  RIP: 0x0000000000400800
  R8 : 0x00000000FFFFFFFF  R9 : 0x00007FFFF7DEA530  R10: 0x0000000000000000  R11: 0x0000000000000282  R12: 0x00000000004006D0
  R13: 0x00007FFFFFFFDEA0  R14: 0x0000000000000000  R15: 0x0000000000000000
  CS: 0033  DS: 0000  ES: 0000  FS: 0000  GS: 0000  SS: 002B				
-----------------------------------------------------------------------------------------------------------------------[code]
=> 0x400800 <main>:	push   r15
   0x400802 <main+2>:	push   r14
   0x400804 <main+4>:	push   rbx
   0x400805 <main+5>:	mov    edi,0x400907
   0x40080a <main+10>:	xor    eax,eax
   0x40080c <main+12>:	call   0x400660 <printf@plt>
   0x400811 <main+17>:	mov    rdi,QWORD PTR [rip+0x225788]        # 0x625fa0 <stdout@@GLIBC_2.2.5>
   0x400818 <main+24>:	call   0x4006a0 <fflush@plt>
-----------------------------------------------------------------------------------------------------------------------------

Breakpoint 2, 0x0000000000400800 in main ()
gdb$ 
}}}

Now, the program stopped at main :) and we can continue with our debugging session.