[davidtgoldblatt]

> Maybe there is a way to paper over this in the glibc implementation of free_sized (rather than calling free unconditionally), and still do something useful for the glibc allocator. I don't know.

We emailed about this a little contemporaneously (thread "Sized deallocation for C", from February), and I think we came to the conclusion that glibc can make interposition work seamlessly even for interposed allocators lacking free_sized, by checking (in glibc's free_sized) if the glibc malloc/calloc/realloc has been called, and redirecting to free if it hasn't. (The poorly-named "Application Life-Cycle" section of the paper).