On a gentoo hardened musl new system, xterm fails to start. There is a patch from alpine linux that fix the problem: https://git.alpinelinux.org/aports/tree/community/xterm/posix-ptys.patch?h=3.10-stable
Confirmed. I have been able to duplicate this issue. When started xterm produces: open ttydev: I/O error open ttydev: I/O error open ttydev: I/O error open ttydev: I/O error .... With the applied patch xterm starts normally.
Verified same issue here also. Patch fixes on -351 and -353. @johu, do you might carrying patch in ::gentoo ? shouldn't affect glibc builds adversely.