http://benji3up2kxewkqfcq7buxk2xd6zwy3zggnurkrm3l4cvwy2iipvyyad.onion/mirrors/gmpdoc/Notes-for-Particular-Systems.html
This makes that code unsuitable for use with the special V9
‘ -mcmodel=embmedany ’ (which uses g4 as a data segment pointer), and
for applications wanting to use those registers for special purposes.