exec hang at boot.
I might have found the trigger for the exec hang at boot. The symptoms
were that very early during the program loading by ld.so, it would
overflow its stack with 0x40, apparently because there were odd things
happening with the GOT. One odd thing was that ld.so was getting loaded
at 0x0. That's because it is a PIE. Issues that might come up are that
pointer 0x0 could then actually be a should-be-valid pointer... I
modified gnumach to load PIE binaries at 0x8000000, like our exec server
does, and couldn't reproduce the exec hang at boot. This is now in
debian as gnumach version 2:1.8+git20201007-1.