The free_sized function is kind of a bad example, though. For years to come, using free_sized will break malloc interposition. Interposed mallocs will not support free_sized initially. (It's currently not in jemalloc, tcmalloc, mimalloc as far as I can see.) If we add it to glibc and your application picks it up, calls to free_sized will end up with the glibc allocator even if malloc/free/… have been interposed. 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.
> 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).
