Fil-C's understanding of memory safety is not "its own" idiosyncratic made up definition. Memory safety in the whole tradition that includes CHERI etc is defined in terms of objects and allocations. In C structs and arrays are not object boundaries. So CHERI will have the same semantics as Fil-C in your struct example, unless you enable a compatibility-breaking mode, which Fil-C could very plausibly acquire too, at the same cost of breaking semantic compatibility with the C/C++ semantics.
As far as I know calling free is optional with Fil-C. It can prevent situations where some memory is no longer needed but isn't freed due to some remaining pointer to it sitting around somewhere, but it's not required. The GC will act like a GC if given the opportunity.
There is an unsafe call primitive in stdfil that was used to support constant time crypto functions when Fil-C didn't have support for inline assembly.
Fil-C now has support for inline assembly, so it's not needed anymore, and I believe indeed the intention is to remove it, since Fil-C is not supposed to have any unsafe hatches.
Fil-C is not Linux only by design, that's completely false.
By the way, if you don't want a culture war, you gotta stop warring.
> Fil-C now has support for inline assembly, so it's not needed anymore, and I believe indeed the intention is to remove it, since Fil-C is not supposed to have any unsafe hatches.
See, this is nuance! Nuance is good! But you can't go around saying "fil-c has no escape hatches" when it has one, even if that one is planned on being removed.
> Fil-C is not Linux only by design, that's completely false.
Can you explain to me how it would work on other platforms? It currently does not, and I don't see how it can. Or at least, not without more "escape hatches."
On non-Linux platforms, you must go through a system provided shared library rather than make syscalls directly. fil-c has its own ABI, and so it has its own libc that uses it. You cannot recompile those other systems's libc (or equivalent) with fil-c, therefore, the strategy used on Linux cannot work.
This is one reason why Rust has unsafe: you have to interact with inherently unsafe APIs in order to do anything meaningful with the operating system. fil-c needs an equivalent of some kind, and so isn't better or worse here, it's just the reality of how these systems work.
>you must go through a system provided shared library rather than make syscalls directly
Just to add to this, on Windows for example you're really only supposed to invoke syscalls via ntdll as the syscall table is not stable so their numbering changes over time. You cannot guarantee forward or backward compat if you do not use the library.
> I do not go around posting "omg Rust is SO MUCH BETTER than zig or fil-c, which are TRASH." I talk about engineering tradeoffs, and what matters to me personally. I do not say "if you use Zig, you are a bad person." I am not saying that any comparison is bad. I am saying that the way that the comparison is presented is bad. That is different.
Oh, who is saying things like that? Do you mean to imply that this kind of vitriol is characteristic of the Fil-C project?
The same basically holds for proofs in the absence of coherent global correctness criteria like, say, confluence and normalization for a lambda calculus, or soundness and completeness for a logic.
Fable's napkin estimate of the effort required to produce a passable reference semantics for Postgres, which would involve novel discoveries in denotational semantics of concurrent transactions and so on, might be in the ballpark of 30–60 years of PhD level work.
So realistically I think the only way to validate a Postgres implementation involves differential testing, fuzzing, acceptance test suites, etc. And still you'll have bugs that need to be hammered out the good old fashioned way.
This is a description of an imaginary compiler, evoked by the ANSI/ISO standards documents, which has never existed and will never exist. To understand what the program will do, you just have to understand the compiler behavior on your target platforms. A helpful intuition pump is: imagine the ANSI/ISO specifications simply do not exist; now what? Well, you just continue your engineering practice, the way you would for any of the myriad languages that never even had a post hoc standards document.
That word is carrying a lot of weight here. Compilers are unbelievably complex these days, and it's impossible for any one human to fully understand the entire compilation process, including the effects of any arbitrary combination of compiler flags.
Any assumptions you have about what the compiler does in the face of UB will collapse on the next patch release of that compiler, or the moment somebody changes the compiler flags, or the moment somebody tries to compile the code for a slightly different OS, not to mention architecture.
There is no other way to understand what C compilers do than reading the standard.
yeah then I have to learn how it works and what it assumes and how I can control it and maybe switch to a more well behaved compiler if it's truly insane
Every bug is the result of an imaginary computer that doesn't work exactly like my computer does and triggers a bug in my code. The code works on my machine, so this imaginary computer never existed and will never exist.
Signed vs unsigned chars, and the accompanying extension rules, have already bitten me switching between x86/ARM compilers. Confused the hell out of me when I was just starting out with C.
If you're going to interpret C as in "C on amd64, running on Linux 7.0 on an Arrow Lake Intel processor" then yes, you can get away with a lot of UB. That mitigates the problem but doesn't make it go away.
Not imaginary. Eliding checks on nullptr and integer overflow were both implemented, shipped, miscompiled the linux kernel and grew flags to disable them. I expect there are more if one goes looking.
Well yeah that just means some aspects of the imaginary compiler were in some configurations approximated by some historical compiler versions and were in some cases rejected by the community (which cares about sane semantics even for behavior left undefined by ANSI/ISO) and in some cases left in as defaults but made trivially configurable for anyone who wants to define the undefined behavior.
Right, good example, and both GCC and Clang offer well understood parameters for deciding, per compilation unit, what behavior you want for signed overflow (-fwrapv, -fno-strict-overflow, etc), so in reality it's quite far from spooky arbitrary nasal demons.
> But also, what you describe would be incorrect, since two <MAX values can add to a value that is >MAX, and overflow
I was maybe unclear. I meant, if you know a sum can introduce overflow (because you have a check right after), why not check the inputs before doing the sum, instead of checking the sum?
(y > 0 && x > INT_MAX - y)
|| (y < 0 && x < INT_MIN - y)
and hope the optimizer turns it back into just checking the result. Or you use -fwrapv to concretize the ISO ambiguity and specify the natural two's complement semantics, checking overflow with the classic Hacker's Delight formula;
((x ^ s) & (y ^ s)) < 0
But the best way is to use the intrinsic __builtin_add_overflow or, depending on compiler support, its C23 standardization via <stdckdint.h> and ckd_add etc.
UB doesn't mean that it is not specified (actually it is often very well specified), it means that compilers can and do assume that such code patterns will not be present. Those cases may not be considered and can lead to unexpected behaviour.
Additionally, some (most?) UB is intentionally UB so that optimisers are free to do fancy tricks assuming that certain cases will never happen. Indeed, this is required for high performance. If they do happen, again, it can lead to unexpected behaviour.
PS: Most languages that don't have a specification declare their primary implementation to be specification-as-code. Rust is an example of that, and it does still have UB: the cases that the compiler assumes will not happen.
undefined behavior is the behavior of code patterns "for which this International Standard imposes no requirements" and the behavior is in fact almost always predictable and agreed upon by compiler vendors and the users of the language, which is why you are able to use programs that rely on undefined behavior probably every single second you are using the computer
edit: for example I'm typing this into Safari which means probably every key press and event is going through JSC JIT compiled functions—which have, structurally and necessarily and intentionally, COMPLETELY undefined behavior according to the spec—and yet it miraculously works, perfectly, because the spec doesn't really matter
If you stop trying to find something like truly ontologically novel about it, you might be able to understand what it actually is. Okay it's not impressive. It's not incredible. It's not groundbreaking new technology. It is what it is.
It is being discussed as though it were ontologically novel, karpathy is saying it's something new and he is an authority, so to me there is something here that i am not seeing. I promise i am not trying to be a naysayer or poke holes, I am literally just trying to find out what the hell it is. I would install it but i don't want to install something without knowing what it does, and what is written in the docs is clear as mud.
It's not new in the sense that any of its components are new, and it's not new in the sense that similar things had not been done before, it's new in the sense that putting the right components together in the right way suddenly created something capable of starting a viral hype.
Essentially, as I understand it, it is a personal AI assistant running on your computer, integrated with different systems (like email, chat).
I am not arguing, merely seeking to understand. I'm not saying it isn't novel. I'm saying that I don't understand what is novel about it and seeking clarity.
The answer seems to be simply that it is all of the extant technologies productized for normies, a la Dropbox. Satisfactory answer, got what I was looking for, thank you! As a dropbox user, I may buy a mac mini and try it :-)
Nontechnical people I know are buying hardware to run claws on. As I understand it, the innovation here isn't the tech but in availability/ease of access.
