[guardian-dev] using -Werror=format-security

[Jacob Appelbaum]

Abel Luck:
> -Werror=format-security
>     "Once this flag is enabled, GCC will refuse to compile code that could be
> vulnerable to a string format security flaw."
> 
> We should investigate adding this flag to our native builds, as well as other hardening
> flags. Not sure if it is available in the NDK though.
> 

If you have a chance, I encourage you to look at the build hardening
we've done in tor and in other projects such as tlsdate:

  https://github.com/ioerror/tlsdate/blob/master/configure.ac#L450

Basically, I suggest you add the following if your compiler supports
these options:

  -D_FORTIFY_SOURCE=2 -fstack-protector-all
  -fwrapv -fPIE -Wstack-protector
  --param=ssp-buffer-size=1

Also, I suggest the following for your linker:

  -z relro -z now
  -pie

All the best,
Jake