New comment by richfelker on void-packages repository

https://github.com/void-linux/void-packages/issues/23557#issuecomment-718392360

Comment:
OK, this turned out to be from `sendmsg` failing with `EMSGSIZE`, which is part of a systemic issue of qemu `linux-user/syscall.c` mixing libc types and raw syscalls. This was introduced in 2016 as part of "safe syscalls" for fixing interaction of emulated syscalls with signals, and the fix basically precluded ever being able to run qemu linux-user guest on non-linux host, and made it hard to run even on a linux host if the libc and kernel uapi types don't entirely match.

Working around the `sendmsg` problem is fairly easy just by making `do_sendrecvmsg_locked` zero-initialize its `struct msghdr`, but there are a large number of othe `safe_*` calls in that file that are making invalid assumptions about libc and kernel types matching, especially in the way of time64 breakage.