The standard doesn't specify any serviceable parts, and I don't think there are any internals of the struct defined in musl libc on Linux (glibc may be a differ

The standard doesn't specify any serviceable parts, and I don't think there are any internals of the struct defined in musl libc on Linux (glibc may be a different story). However, on OpenBSD, it did seem to have some user-visible bits: https://github.com/openbsd/src/commit/b7f6c2eb760a2da367dd51d539ef06f5f3553790#diff-5e1f2789f2dc0618ffb77ce98c2fab185eaedd0897a0326180f0fb4db794e0b3L99-L131 https://github.com/openbsd/src/commit/b7f6c2eb760a2da367dd51... If you expose it, someone will probably sooner or later use it, but probably not in any sane / portable code. On the face of it, it doesn't seem like a consequential change, but maybe they're mopping up after some vulnerability in that one weird package that did touch this.