These are a few examples of hiding certain code-paths from somebody trying to
reverse-engineer a 32- or 64-bit x86 binary via a debugger and/or disassembler.

I read about this in some article many moons ago. Could have been some DefCon-,
BlackHat- or ChaosComputerCongress-material. While it does not make it
impossible to reverse-engineer the binary, it at least makes it a bit more
difficult.

The dependencies are modest:

 * make 4.11
 * nasm 2.11.08
 * gdb 7.11

I compiles and runs under recent Linux-distributions (e.g. Ubuntu 16.04). It
probably also works on recent intel-based MacOS machines, but I've not tested
it, since I was too lazy to figure out the system-call vectors. But the general
principle should apply there too.

How to try it out:

 1> make
 1> ./anti-debug
 No on is looking
 1> gdb ./anti-debug
 (gdb) run
 Starting program: /home/user/src/asm-anti-debug/anti-debug
 I'm being debugged
 [Inferior 1 (process 3266) exited normally]
 (gdb) quit

If you want to be able to step through the stripped binary with gdb use
the provided make-target "info" to obtain the starting address of the
code/text-section of the different example binaries.

 1> gdb ./anti-debug
 (gdb) tui enable
 (gdb) tui reg general
 (gdb) break *0x00400060
 Breakpoint 1 at 0x400060
 (gdb) run
 Starting program: /home/user/src/asm-anti-debug/anti-debug
 Breakpoint 1, 0x00400060 in ?? ()
 (gdb) nexti
 ...

Feedback and patches are welcome.