Apparently this was done intentionally. The rationale given is that we don't want to allow non-safe C to be used in fil-C programs. Fair enough.
But why should we prevent fil-C programs to be used from Rust (or C, for that matter)?
I don't understand much about compilers, but I guess allowing one would also allow the other? i.e. it's not possible to make fil-C ABI compatible with C (so that it can be more easily called), while also not letting you use call C from it?
You're looking too much at the complete memory safety goal; the important part here is the interop non-goal. Designing a foreign function interface between Fil-C and regular C, in a way that upholds both languages' expectations about the environment the code's running in, is a very difficult problem and nobody seems to have much of an idea of how such a thing could work.
I worry that this same problem will doom the extern "Fil-C" idea that this post advocates. Zig is not really an encouraging precedent because Zig's proposed memory-safe mode adds runtime checks to everything just like Fil-C does, whereas the post author wants to avoid those checks for Rust code that's already statically known to be memory-safe. That said, it's possible I'm missing something.
Yes and AFAIK any fil-C program needs to be linked against fil-C compiled libraries, such as libc/musl/etc. I too would like to know what other challenges exist in making this process more automated.
It's not a replacement for Fil-C's role as a precise ASAN/Valgrind, but it works great if you want to call a C library without letting it freely spray caller's memory.
Fil-C is more precise than valgrind or asan. Valgrind and asan will allow a buggy access (like an OOB) to succeed if the resulting address is valid at all - which is useless from a security enforcement perspective since clobbering valid addresses is what the attacker is trying to do.
Fil-C only allows an access to succeed if it’s in bounds of that pointer’s capability. That is a useful level of precision for security, since it prevents the attacker from clobbering the addresses of their choice.
Why isn't fil-C ABI compatible with C?
https://fil-c.org/runtime
Apparently this was done intentionally. The rationale given is that we don't want to allow non-safe C to be used in fil-C programs. Fair enough.
But why should we prevent fil-C programs to be used from Rust (or C, for that matter)?
I don't understand much about compilers, but I guess allowing one would also allow the other? i.e. it's not possible to make fil-C ABI compatible with C (so that it can be more easily called), while also not letting you use call C from it?
You're looking too much at the complete memory safety goal; the important part here is the interop non-goal. Designing a foreign function interface between Fil-C and regular C, in a way that upholds both languages' expectations about the environment the code's running in, is a very difficult problem and nobody seems to have much of an idea of how such a thing could work.
I worry that this same problem will doom the extern "Fil-C" idea that this post advocates. Zig is not really an encouraging precedent because Zig's proposed memory-safe mode adds runtime checks to everything just like Fil-C does, whereas the post author wants to avoid those checks for Rust code that's already statically known to be memory-safe. That said, it's possible I'm missing something.
It's also because Fil-C calls need to carry along a bunch of extra information, to support the safety checks
Yes and AFAIK any fil-C program needs to be linked against fil-C compiled libraries, such as libc/musl/etc. I too would like to know what other challenges exist in making this process more automated.
Correct
There is a solution that Mozilla uses in prod for legacy C codecs:
https://rlbox.dev/
It's not a replacement for Fil-C's role as a precise ASAN/Valgrind, but it works great if you want to call a C library without letting it freely spray caller's memory.
Yeah rlbox is great.
Fil-C is more precise than valgrind or asan. Valgrind and asan will allow a buggy access (like an OOB) to succeed if the resulting address is valid at all - which is useless from a security enforcement perspective since clobbering valid addresses is what the attacker is trying to do.
Fil-C only allows an access to succeed if it’s in bounds of that pointer’s capability. That is a useful level of precision for security, since it prevents the attacker from clobbering the addresses of their choice.