[wahern]

This all seems predicated on the fact that Solaris doesn't support direct system calls and the fact that they ship their kernel and libc as one unified whole (like BSDs). Solaris is free to update the layout of their shared data structures whenever they want[1].

Because Linux kernel interfaces are distinct and separate from libc, and given Linus' policy on backwards compatibility, Linux had two choices for an _interface_: 1) export a data structure to userland that could never change, or 2) export a code linking mechanism to userland that could never change. In that light the latter choice seems far more reasonable.

[1] The shared data structures for this particular feature. There are other kernel data structures that leak through the libc interface and for which Solaris is bound to maintain compatibility.