blhc checks build logs for missing hardening flags. For similar tools, see Package-checking tools. For how to add hardening flags, see Hardening.
"Hardening" is the process of telling your compiler to produce binaries that are better protected against certain types of attack. Hardening and HardeningWalkthrough should be enough for most packages, but complex build systems can sometimes run a compiler without setting all the necessary flags.
blhc scans your compilation log for lines that suggest missing flags. Run it like this:
blhc /path/to/log/file