nothing was "reverse-engineered". Read the article. DT_HASH has been documented in SysV since ages. It's the DT_GNU_HASH that's (almost) undocumented and needs

nothing was "reverse-engineered". Read the article. DT_HASH has been documented in SysV since ages. It's the DT_GNU_HASH that's (almost) undocumented and needs to be reverse-engineered from GNU ld's source code.