alt Hacker NewsHe claims that all syscalls are safe because they're implemented by his custom libc, but that libc then calls out to the system libc, where the system calls are unsafe. He then claims that this is unlike rust, where making a syscall is unsafe. If you stick to the rust standard library in the same way that fil-c programs stick to the fil-c standard library, then all of your rust "system calls" are safe, too.
Someone in the audience also pointed out that a tool like this could be used to compile rust programs, not just C programs, in which case it's odd to hear Fil-C repeatedly framed as a language in opposition to rust rather than as a tool which might complement it.
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Custom libc does not call to system libc.
“Custom” and “system” aren’t the terms I use; I say user libc and you libc (because they are basically the same libc - either both are musl or both are glibc).
User libc calls to the Fil-C runtime, which filters syscalls, and those filtered syscalls are made via yolo libc.
Hence, a Fil-C program is memory safe down to the syscalls and syscalls cannot be used to escape the protections (unless you do weird stuff with /proc)
> Someone in the audience also pointed out that a tool like this could be used to compile rust programs, not just C programs, in which case it's odd to hear Fil-C repeatedly framed as a language in opposition to rust rather than as a tool which might complement it.
You can combine both approaches for sure, but that doesn't change that they are indeed separate approaches. One (Rust) intends to characterize and prevent undefined behavior at compile time, and another (Fil-C) intends to make undefined behavior impossible at runtime, as evidenced by decisions like (for example) making unsafe usage of setjmp/longjmp safe.
You could sort of achieve "safety-in-depth" by combining both approaches, but Rust prefers to prevent all undefined behavior statically, and Fil-C prefers to focus on dynamic approaches. They have real differences, so that's probably what comes off as "oppositional"
indeed, the ideas could be used more widely.
fil-c runs on linux.
what if linux ran on fil-c?
also: why not use fil-c to improve cython, and the ffi.
Both Rust and Fil-C have unsafe blocks, but in Fil-C latter system, only Pizlo gets to write them. Why am I not filled with confidence?
Rust doesn't runtime validate that your usage of syscalls is memory safe, while Fil-C does. For example you can call mmap in Fil-C and it is still guaranteed to be memory safe, while in Rust you can easily violate memory safety by calling mmap. This seems like an unambiguous improvement to me. This is as memory safe as it is possible to be on a system with a kernel that is not memory safe.
Adding Fil-C-like runtime checks to Rust is definitely an interesting direction.