> But it does not nearly approach the level of systematic prevention of memory unsafety that rust achieves.
Unless I gravely misunderstood Zig when I learned it, the Zig approach to memory safety is to just write a ton of tests fully exercising your functions and let the test allocators find and log all your bugs for you. Not my favorite approach, but your article doesn't seem to take into account this entirely different mechanism.
Yes, testing is Zig's answer. But that quote is right. Testing doesn't achieve the same kind of systematic prevention of memory bugs that rust does. (Or GC based languages like Go, Java, JS, etc.).
You can write tests to find bugs in any language. C + Valgrind will do most of the same thing for C that the debug allocator will do for zig. But that doesn't stop the avalanche of memory safety bugs in production C code.
I used to write a lot of javascript. At the time I swore by testing. "You need testing anyway - why not use it to find other kinds of bugs too?". Eventually I started writing more and more typescript, and now I can't go back. One day I ported a library I wrote for JSON based operational transform from javascript to typescript. That library has an insane 3:1 test:code ratio or something, and deterministic constraint testing. Despite all of that testing, the typescript type checker still found a previously unknown bug in my codebase.
As the saying goes, tests can only prove the presence of bugs. They cannot prove your code does not have bugs. For that, you need other approaches - like rust's borrow checker or a runtime GC.
There's also no reason to have a separate borrow checker if it could just be integrated in the compiler.
When a compiler has a borrow checker that means the language was already designed to enable borrow checking in the first place. And if a language can let you do borrow checking why would you use a separate tool?
because it gets it out of the fast path compile cycle. do you need a borrow checker for `ls`? Probably not. don't use it. do you need it every time you work through intermediate ideas in a refactor? probably not. just turn it on in CI.
> do you need a borrow checker for `ls`? Probably not.
Does ls use references and objects with lifetimes? I bet it does. And if so, the answer is yes. You do need the borrow checker in rust to make sure it uses memory and lifetimes correctly.
If your program somehow doesn’t use references or owned objects, then the borrow checker doesn’t have any work to do. So there’s no harm done in leaving it on.
The borrow checker is not the slow part of the Rust compiler and lets me avoid bugs, why would I not always want to use it?
And if you put the borrow checker in the CI you massively increased the latency between writing the code and getting all relevant feedback from the compiler/tooling. This would do the opposite of what you intended.
"But seatbelts would also work if everybody was just choosing to use them rather than us mandating their fitment and use, so I don't understand why facts are true"
Amusingly this is even true for the linter, nobody ran the C linter, more or less everybody runs the Rust linter, the resulting improvement in code quality is everything you'd hope. All humans love to believe they're above average, most are not and average is by definition a mediocre aspiration. Do better.
what the hell are you talking about. if you are writing security conscious software you should turn on a static checker and proudly show a badge that says "this code is memory safe". if youre writing a custom data pipeline to be used in a niche scientific field where the consumers are you and anyone that wants to repro your pipeline, and everything is in arenas, who the fuck cares. don't bother with static analysis.
If everything is in arenas, lifetimes get much easier.
But, the borrow checker doesn't just check lifetimes. It also checks ownership, and that variables either have a single mutable reference or immutable references. The optimizer assumes those invariants are maintained in the code. Many of its optimizations wouldn't be sound otherwise.
So, if you could compile code which fails the borrow checker, there's all sorts of weird and wonderful sources of UB eagerly waiting to give you a really bad day - from aliasing issues to thread safety problems to use-after-free bugs. The borrow checker has been around forever in rust. So I don't think anyone has any idea what the implications would be of compiling "bad" code.
I suppose you can even ship the test/logging allocator with your production build, and instruct your users to run your program with some option / env var set to activate it. This would allow to repro a problem right where it happens, hopefully with some info helpful for debugging attached.
Not a great approach for critical software, but may be much better than what C++ normally offers for e.g. game software, where the development speed definitely trumps correctness.
What that means, though, is that you have a choice between defining memory unsafely away completely with Rust or Swift, or trying to catch memory problems by a writing a bunch of additional code in Zig.
I’d argue that ‘a bunch of additional code’ to solve for memory safety is exactly what you’re doing in the ‘defining memory safety away’ example with Rust or Swift.
It’s just code you didn’t write and thus likely don’t understand as well.
This can potentially lead to performance and/or control flow issues that get incredibly difficult to debug.
That sounds a bit unfair. All that code that we neither wrote nor understood, I think in the case of Rust, it’s either the borrow checker or the compiler itself doing something it does best - i.e., “defining memory safety away”. If that’s the case, then labeling such tooling and language-enforced memory safety mechanisms as “a bunch of additional code…you didn’t write and…don’t understand” appears somewhat inaccurate, no?
So? That wasn't the claim. The GP poster said this:
> This can potentially lead to performance and/or control flow issues that get incredibly difficult to debug.
Writing a linked list in rust isn't difficult because of control flow issues, or because rust makes code harder to debug. (If you've spent any time in rust, you quickly learn that the opposite is true.) Linked lists are simply a bad match up for the constraints rust's borrow checker puts on your code.
In the same way, writing an OS kernel or a high performance b-tree is a hard problem for javascript. So what? Every language has things its bad at. Design your program differently or use a different language.
> This can potentially lead to performance and/or control flow issues that get incredibly difficult to debug.
The borrow checker only runs at compile-time. It doesn't change the semantic meaning - or the resulting performance - of your code.
The borrow checker makes rust a much more difficult and frustrating language to learn. The compiler will refuse to compile your code entirely if you violate its rules. But there's nothing magical going on in the compiler that changes your program. A rust binary is almost identical to the equivalent C binary.
Weird that Swift is your totem for "managed/collected runtime" and not Java (or C#/.NET, or Go, or even Javascript). I mean, it fits the bill, but it's hardly the best didactic choice.
The point was that basically no one knows Swift, and everyone knows Java. If you want to point out a memory safe language in the "managed garbage-collected runtime" family, you probably shouldn't pick Swift.
I wouldn’t put Swift in the same ‘managed garbage-collected runtime’ family as Java, C#/.NET, Go, and Javascript, so maybe they weren’t trying to do what you think.
Swift is more like a native systems programming language that makes it easy to trade performance for ergonomics (and does so by default).
What if -- stay with me now -- what if we solved it by just writing vastly less code, and having actually reusable code, instead of reinventing every type of wheel in every project? Maybe that's the real secret to sound code. Actual code reuse. I know it's a pipedream, but a man can dream, can't he?
The way we've done code reuse up to this point rarely lives up to its promises.
I don't know what the solution is, but these days I'm a lot more likely to simply copy code over to a new project rather than try to build general purpose libraries.
I feel like that's part of the mess Rust/Swift are getting themselves tangled up in, everything depends on everything which turns evolution into more and more of an uphill struggle.
Why? In C I'd understand. But cargo and the swift package manager work great.
By all means, rewrite little libraries instead of pulling in big ones. But if you're literally copy+pasting code between projects, it doesn't take much work to pull that code out into a shared library.
Yeah that is the opposite take of recent posts that the Cargo/npm package dependence is way too heavy.
Saying we should rely on reusable modules is great and all, but that reusable code is going to be maintained by who now?
There's no sustainable pattern for this yet, most things are good graces of businesses or free time development, many become unmaintained over time- people who actually want to survive on developing and supporting reusable modules alone might actually be more rare than the unicorn devs.
False. Fil-C secures C and C++. It’s more comprehensively safe than Rust (Fil-C has no escape hatches). And it’s compatible enough with C/C++ that you can think of it as an alternate clang target.
Fil-C is impressive and neat, but it does add a runtime to enforce memory safety which has a (in most cases acceptable) cost. That's a reasonable strategy, Java and many other langs took this approach. In research, languages like Dala are applying this approach to safe concurrency.
Rust attempts to enforce its guarantees statically which has the advantage of no runtime overhead but the disadvantage of no runtime knowledge.
> but in practice fails, because of pervasive use of `unsafe`.
Yes, in `unsafe` code typically dynamic checks or careful manual review is needed. However, most code is not `unsafe` and `unsafe` code is wrapped in safe APIs.
I'm aware C already has a runtime, this adds to it.
> Yes, in `unsafe` code typically dynamic checks or careful manual review is needed. However, most code is not `unsafe` and `unsafe` code is wrapped in safe APIs.
Those are the excuses I heard from C++ programmers for years.
Memory safety is about guarantees enforced by the compiler. `unsafe` isn't that.
The stuff Fil-C adds is on the same footing as `unsafe` code in Rust- its implementation isn't checked, but its surface area is designed so that (if the implementation is correct) the rest of the program can't break it.
Whether the amount and quality of this kind of code is comparable between the two approaches depends on the specific programs you're writing. Static checking, which can also be applied in more fine-grained ways to parts of the runtime (or its moral equivalent) is an interesting approach, depending on your goals.
> The stuff Fil-C adds is on the same footing as `unsafe` code in Rust- its implementation isn't checked, but its surface area is designed so that (if the implementation is correct) the rest of the program can't break it.
It’s not the same.
The Fil-C runtime is the same runtime in every client of Fil-C. It’s a single common trusted compute base and there’s no reason for it to grow.
On the other hand Rust programmers use unsafe all over the place, not just in some core libraries.
Yeah, that's what I meant by "depends on the specific programs you're writing." Confining unsafe Rust to core libraries is totally something people do.
> Fil-C achieves this using a combination of concurrent garbage collection and invisible capabilities (each pointer in memory has a corresponding capability, not visible to the C address space)
In almost all uses of C and C++, the language already has a runtime. In the Gnu universe, it's the combination of libgcc, the loader, the various crt entrypoints, and libc. In the Apple version, it's libcompiler_rt and libSystem.
Fil-C certainly adds more to the runtime, but it's not like there was no runtime before.
It makes it a lot less performant and there is no avoiding or mitigating that downside. C++ is often selected as a language instead of safer options for its unusual performance characteristics even among systems languages in practice.
Fil-C is not a replacement for C++ generally, that oversells it. It might be a replacement for some C++ software without stringent performance requirements or a rigorously performance-engineered architecture. There is a lot of this software, often legacy.
> It makes it a lot less performant and there is no avoiding or mitigating that downside.
You can’t possibly know that.
> C++ is often selected as a language instead of safer options for its unusual performance characteristics even among systems languages in practice.
Is that why sudo, bash, coreutils, and ssh are written in C?
Of course not.
C and C++ are often chosen because they make systems programming possible at all due to their direct access to syscall ABI.
> Fil-C is not a replacement for C++ generally, that oversells it.
I have made no such claim.
Fil-C means you cannot claim - as TFA claims - that it’s impossible to make C and C++ safe. You have to now hedge that claim with additional caveats about performance. And even then you’re on thin ice since the top perf problems in Fil-C are due to immaturity of its implementation (like the fact that linking is hella cheesy and the ABI is even cheesier).
> It might be a replacement for some C++ software without stringent performance requirements or a rigorously performance-engineered architecture. There is a lot of this software, often legacy.
It’s the opposite in my experience. For example, xzutils and simdutf have super lower overhead in Fil-C. In the case of SIMD code it’s because using SIMD amortizes Fil-C’s overheads.
> C and C++ are often chosen because they make systems programming possible at all due to their direct access to syscall ABI.
Surely Fil-C cannot provide direct access to syscalls without violating the safety guarantee. There must be something ensuring that what the kernel interprets as a pointer is actually a valid pointer.
> Fil-C means you cannot claim - as TFA claims - that it’s impossible to make C and C++ safe. You have to now hedge that claim with additional caveats about performance. And even then you’re on thin ice since the top perf problems in Fil-C are due to immaturity of its implementation (like the fact that linking is hella cheesy and the ABI is even cheesier).
The world of compilers is littered with corpses of projects that spent years claiming faster performance was right around the corner.
I believe you can make it faster, but how much faster? We'll see.
I think these types of compatibility layers will be a great option moving forward for legacy software. But I have a hard time seeing the case for using Fil-C for new code: all the known disadvantages of C and C++, now combined with performance closer to Java than Rust (if not worse), and high difficulty interoperating with other native code (normally C and C++'s strength!), in exchange for marginal safety improvements over Rust (minus Rust's more general safety culture).
edit: I feel bad writing such a dismissive comment, but it's hard to avoid reacting that way when I see unrealistically rosy portrayals of projects.
Fil-C’s perf sucks on some workloads. And it doesn’t suck on others.
Extreme examples to give you an idea:
- xzutils had about 1.2x overhead. So slower but totally usable.
- no noticeable overhead in shells, systems utilities, ssh, curl, etc. But that’s because they’re IO bound.
- 4x or sometimes maybe even higher overheads for things like JS engines, CPython, Lua, Tcl, etc. Also OpenSSL perf tests are around 4x I think.
But you’re on thin ice if you say that this is a reason why Fil-C will fail. So much of Fil-C’s overhead is due to known issues that I will fix eventually, like the function call ABI (which is hella cheesy right now because I just wanted to have something that works and haven’t actually made it good yet).
One of these days, a project will catch on that's vastly simpler than any memory solution today, yet solves all the same problems, and more robustly too, just like how it took humanity thousands of years to realize how to use levers to build complex machines. The solution is probably sitting right under our noses. I'm not sure it's your project (maybe it is) but I bet this will happen.
That’s a really great attitude! And I think you’re right!
I think in addition to possibly being the solution to safety for someone, Fil-C is helping to elucidate what memory safe systems programming could look like and that might lead to someone building something even better
There is a third category of memory and other software safety mechanisms: model checking. While it does involve compiling software to a different target -- typically an SMT solver -- it is not a compile-time mechanism like in Rust.
Kani is a model checker for Rust, and CBMC is a model checker for C. I'm not aware of one (yet!) for Zig, but it would not be difficult to build a port. Both Kani and CBMC compile down to goto-c, which is then converted to formulas in an SMT solver.
There isn't a real one yet, but to scratch an itch I tried to build one for Zig. It's not complete nor do I have plans to complete it. https://github.com/ityonemo/clr
If zig locks down the AIR (intermediate representation at the function level) it would be ideal for running model checking of various sorts. Just by looking at AIR I found it possible to:
- identify stack pointer leakage
- basic borrow checking
- detect memory leaks
- assign units to variables and track when units are incompatible
If you're filling uninitialized pointers with AAAAAAAA, it might be best to also reserve that memory page and mark it as no-access.
I'm not even joking. Any pattern used by magic numbers that fill pointers (such as HeapFree filling memory with FEEEEEEE on Windows) should have a corresponding no-access page just to ensure that the program will instantly fail, and not have a valid memory allocation mapped in there. For 32-bit programs, everything past 0x8000000 used to be reserved as kernel memory, and have an access violation when you access it, so the magic numbers were all above 0x80000000. But with large address aware programs, you don't get that anymore, only manually reserving the 4K memory pages containing the magic numbers will give you the same effect.
Maybe not Zig the language, but the fact that all allocating functions in the standard library accept an allocator (and community libraries follow this precedent) does give you much more control in practice.
For example, how would you use a Vec using stack memory for elements, instead of the heap? For the equivalent data structure in Zig (std.ArrayList), it's just a matter of using a stack allocator instead of using a heap allocator, which is an explicit decision either way.
> For example, how would you use a Vec using stack memory for elements, instead of the heap? For the equivalent data structure in Zig (std.ArrayList), it's just a matter of using a stack allocator instead of using a heap allocator, which is an explicit decision either way.
In Rust it would likewise "just" be a matter of using the allocator we want. In this specific case we can see that's nonsense - there's a single stack pointer in the CPU so while it's perfectly possible to make two growable arrays (Vec or ArrayList depending on the language) on the heap, if we use the stack instead they're both obliged to somehow share that single stack pointer when growing, thus whether Zig or Rust this idea can't actually work, but for examples which do work the Rust and Zig doesn't look that different.
Welcome to the magic of Zig, where ideas that can't actually work actually do work :-)
const std = @import("std");
pub fn main() !void {
var not_heap_memory: [1024]u8 = undefined;
var fixed_buffer_allocator = std.heap.FixedBufferAllocator.init(¬_heap_memory);
const allocator = fixed_buffer_allocator.allocator();
var my_list = std.ArrayList(i32).init(allocator);
defer my_list.deinit();
// notice the try! allocation may fail!
try my_list.append(1);
try my_list.append(2);
for (my_list.items) |d| {
std.debug.print("{}\n", .{d});
}
}
The value here is not that you have unbounded stack memory - obviously. The value is that you can use the same API for a growable list (std.ArrayList) backed by stack memory, as you would for a growable list backed by heap memory. This could be useful if you have a function that accepts an ArrayList as an argument and will append to it, but you have a known maximum size for the ArrayList in the context that you're using it. You cannot use the standard Vec type in the same way in Rust. You cannot use any data structures from the Rust standard library that do allocations in the same way.
Yes, of course, you can make data structures that accept custom allocators in the same way in Rust. Maybe there are even community libraries that do it already. The problem is that because they're not in the standard library, you're going to have a hard time using those data structures with any other community libraries. And thus, in practice, you have less control over your allocation strategies in Rust than you do in Zig.
> The problem is that because they're not in the standard library, you're going to have a hard time using those data structures with any other community libraries.
No, all the Rust standard library collections do in fact have the same feature, you can in fact Vec::new_in(SomeAllocator) - my guess is that you'll say "Ah, but that's not yet in stable Rust" and that'd make sense in other contexts but it's a weird objection when the entire Zig language still isn't 1.0.
If you wanted to write a function which takes a container and adds things to it, which I wouldn't recommend, in Rust you'd write that as a polymorphic function, so it'll just get monomorphized for the SomeAllocator variant.
The use of FixedBufferAllocator here is absurd, indeed it's hard to think of non-absurd uses for this allocator, it's a toy because it has no reclamation.
ArrayList has a slightly weird variation on the 1.5x growth pattern, for a large T the ArrayList<T> will grow something like 1, 2, 4, 7, 11, 17, 26, etc. But with your 1024 byte FixedBufferAllocator, the older sizes are just discarded so somewhere around 62 or so items it'll blow up, all the rest of the space was just thrown away and so the growth fails
Overall this not only doesn't do what you said you were doing originally (it's not actually a stack† allocated growable array, those simply don't exist), it also doesn't do the thing you ostensibly claim it's useful for either, so much of Zig feels like this.
† Edited: For a few minute this said "heap" due to a thinko
Unless I gravely misunderstood Zig when I learned it, the Zig approach to memory safety is to just write a ton of tests fully exercising your functions and let the test allocators find and log all your bugs for you. Not my favorite approach, but your article doesn't seem to take into account this entirely different mechanism.