However, I would imagine (not having looked at the problem in depth) that one would want to be able to use things like Vec<T> or CString from the Rust standard library when implementing a DNS resolver. Since the Rust standard library depends on libc, I'm not sure how one would properly allow the Rust symbols to replace the linked-in libc symbols while still depending on the rest of libc. Maybe it's not an issue? Maybe there's some magic which could be done?
Nonetheless, I mostly started doing this to see if it could be done, not to prove any point (although I'd love it if a point is proven along the way), so a bottom-up approach with #![no_std] was the easiest way to prevent any sort of cyclic dependencies and/or linker issues.
> Since the Rust standard library depends on libc, I'm not sure how one would properly allow the Rust symbols to replace the linked-in libc symbols while still depending on the rest of libc. Maybe it's not an issue? Maybe there's some magic which could be done?
Static libraries can have circular dependencies like that. For example, in ring[1] I have C code in one static library, which calls some Rust functions in my Rust code. And, that Rust code calls functions in the C static library. The linker...links them together.
Circular dependencies are different than duplicate symbols, though, yes? Anyways, my point is not that it's impossible, but that I'm already working at the edge of my knowledge, and I picked the lowest-risk/smallest-chunk pieces of work to get started.
On Linux, the symbols in glibc are marked as "weak"---that is, if the symbol "malloc" isn't found in another object file, then the one in glibc is used. It's that way so that users can override system provided functions (non-"weak" symbols that are duplicated are considered an error).
However, I would imagine (not having looked at the problem in depth) that one would want to be able to use things like Vec<T> or CString from the Rust standard library when implementing a DNS resolver. Since the Rust standard library depends on libc, I'm not sure how one would properly allow the Rust symbols to replace the linked-in libc symbols while still depending on the rest of libc. Maybe it's not an issue? Maybe there's some magic which could be done?
Nonetheless, I mostly started doing this to see if it could be done, not to prove any point (although I'd love it if a point is proven along the way), so a bottom-up approach with #![no_std] was the easiest way to prevent any sort of cyclic dependencies and/or linker issues.