No true Scotsman.

> The whole point of a good mempool is that you malloc once, and only call free when you exit the program. The data structures for memory allocation will never get corrupted. And the memory pool will never release chunk twice cause it keeps tracks of allocated chunks.

Then you've just moved the same problem one layer up - "use after returned to mempool" takes the place of "use after free" and causes the same kind of problems.

> When you allocate, you get a struct back that contains a pointer to the data. When you release, that pointer is zeroed out.

And the program - or, more likely, library code that it called - still has a copy of that pointer that it made when it was valid?

For example, in that implementation, you request memory from a mempool, it returns a chunk-struct with the pointer to allocated memory, the size of the chunk, and optionally some convenience functions for safe access (making sure that the pointer is not incremented or decremented beyond the limits). It also keeps its own pointer to the chunk-struct, along with the chunk that it was allocated. When you release the chunk, it zeros out the pointer in the chunk-struct. Now any access to it will cause a segfault.

You can of course write code that bypasses all those checks, but in Rust, thats equivalent to using unsafe when you wanna be lazy. Also you could argue that Rust is better because instead of segfaulting, the check will be caught during compile time, which is true but only for fairly simple programs. Once you start using RefCells, you cannot guarantee everything during compile time.

The difference is that most of the Rust ecosystem is set up to allow you to not use unsafe. Whereas whenever you use a library in C, you need to pass it a pointer, so bypassing these checks has to be routine. (Note that the article claims as a key merit that it's possible to add annotations to existing libraries)

> When you release the chunk, it zeros out the pointer in the chunk-struct. Now any access to it will cause a segfault.

Only if you're very lucky. Null pointer dereference is undefined behaviour, so it may cause a different thread to segfault on a seemingly unrelated line, or your program may silently continue with subtly corrupted state in memory, or...

> Also you could argue that Rust is better because instead of segfaulting, the check will be caught during compile time, which is true but only for fairly simple programs. Once you start using RefCells, you cannot guarantee everything during compile time.

Using RefCells should be (and, idiomatically, is) the exception rather than the rule. And incorrect use of RefCell results in a safe panic rather than undefined behaviour.

>Whereas whenever you use a library in C, you need to pass it a pointer,

When it comes to developing with Rust, any performance oriented project is necessarily going to have lots of unsafe for interacting with C libraries in the linux kernel in the same way that C code does.

As for comparison to fully safe Rust code outside the unsafes, you can largely accomplish analogous behavior in C with good mempool implementation. Or if you don't need to pass around huge amount of data, you can also do it by simply just never mallocing and using stack variables. There is still some things you have to worry about (using safe length bounded memory copy/move functions, using [type]* const pointer values to essentially make them act like references for function parameters, some other small things).

The point is Rust isn't the defacto standard for memory safety, and while it can exist as its own project, porting its semantics to other languages is not worth it.

Attempting access to a zero address will segfault on most hardware, but unfortunately common C compilers in common configurations will not reliably compile a null pointer dereference to an access to the zero address. Look up why the Linux kernel builds with -fno-delete-null-pointer-checks (sadly, most applications and libraries don't).

> When it comes to developing with Rust, any performance oriented project is necessarily going to have lots of unsafe for interacting with C libraries in the linux kernel in the same way that C code does.

I'm not talking about performance oriented projects. I'm talking about regular use of libraries e.g. I need to talk to PostgreSQL so I'll call libpq, I need to uncompress some data so I'll use zlib, I need to make a HTTP call so I'll use libcurl...

> The point is Rust isn't the defacto standard for memory safety

It absolutely is though. It's got clear, easy-to-assess rules for whether a project is memory-safe or not, and a substantial ecosystem that follows them; so far it's essentially unique in that unless you include GCed languages.

And whatever criticism is you have of that is surpassed by the fact in all cases for regular software (i.e run on a server or laptop or desktop) that would be normal to write in either Rust or C, if it was written in C, and a null pointer is dereferences, it would absolutely crash (i.e Rust is not really being used to develop embedded system software code in non experimental workflows where zero address is a valid memory address).

And whatever criticism you have of that is surpassed by the fact that if you can write Rust code with all the borrowing semantics, you can also write a quick macro for any dereference of a mempool region that checks if the pointer is null and use that everywhere in your code.

So TLDR, not hard to write memory safe code. Rust is just a way to do it, but not the only way. Its great for enterprise projects, much in the same way that Java came up because of its strictness, GC and multi platform capability. And just like Java today, eventually nobody is going to take it seriously, people who want to get shit done will be writing something that looks like python except even higher level, with ai assistants that replace text, and then LLMs will translate that code into the most efficient machine code.

Most people don't though. Even if your code was compiled with it, libraries you use may not have been compiled that way. And even if you do, it doesn't cover all cases.

> And whatever criticism is you have of that is surpassed by the fact in all cases for regular software (i.e run on a server or laptop or desktop) that would be normal to write in either Rust or C, if it was written in C, and a null pointer is dereferences, it would absolutely crash

No it won't. Not reliably, not consistently. It's undefined behaviour, so a C compiler can do random other things with your code, and both GCC and Clang do.

> And whatever criticism you have of that is surpassed by the fact that if you can write Rust code with all the borrowing semantics, you can also write a quick macro for any dereference of a mempool region that checks if the pointer is null and use that everywhere in your code.

"Everywhere in your code" only if you're not using any libraries.

> So TLDR, not hard to write memory safe code.

If it's that easy why has no-one done it? Where can I find published C programs written this way? Like most claims of "safe C", this is vaporware.

Give me an example of a null pointer dereference in a program that one compiles -with -fdelete-null-pointer-checks that doesn't crash when its run on any smartphone, x64 cpu in modern laptops/desktops/servers or Apple Silicon.

https://blog.llvm.org/2011/05/what-every-c-programmer-should... has an example under "Debugging Optimized Code May Not Make Any Sense" - in that case the release build fortuitously did what the programmer wanted, but the same behaviour could easily cause disaster (e.g. imagine you have two different global "init" functions and your code is set up to call one or other of them depending on some settings or something, and you forget to set one of your global function pointers in one of those init functions. Now instead of crashing, calls via that global function pointer will silently call the wrong version of the function).

    #include <ownership.h>
    #include <stdio.h>

    int main()
    {
      FILE *owner f = fopen("file.txt", "r"); 
      if (f)
        fclose(f);
    }

C programmers uses contracts, these contracts are part of documentation of some API. For instance, if you call fopen you must call fclose.

All we need is to create contracts that the compiler can read and verify automatically.

So you're describing fork() and _exit(). That's my favorite memory manager. For example, chibicc never calls free() and instead just forks a process for each item of work in the compile pipeline. It makes the codebase infinitely simpler. Rui literally solved memory leaks! No idea what you're talking about.

Additionally, compilers often offer the option to compile multiple files. Therefore, we cannot afford to leak memory with each file compilation.

Initially I was planning a global allocator for cake source. It had a lot of memory leaks that would be solved in the future.

When ownership checks were added it was a perfect candidate for fixing leaks. (actually I also had this in mind)

The difference with cake ownership and RAII , is that with C++ RAII, the destructor is unconditionally called at end of scope. Then flow analysis is not required in RAII.

Cake requires flow analysis because "destructor" is not unconditionally called.

When the compiler can see that the owner is not owning a object (because the pointer is null for instance) then the "destructor" is not necessary.

To understand the difference.

With flow analysis (how it works today)

    int main() 
    {
      FILE *owner f = fopen("file.txt", "r"); 
      if (f)
        fclose(f);
    }

    void fclose2(FILE * owner p) {
       if (p) fclose(p);
    }

    int main() 
    {
      FILE *owner f = fopen("file.txt", "r"); 
      if (f){
      }
      fclose2(f);
    }

    struct X x = {0};
    //...
    view struct X x2 = x;
    destroy(&x);
    //x2 does not need destructor

Owner pointers take on the responsibility of owning the pointed object and its associated memory, treating them as distinct entities. A common practice is to implement a delete function to release both resources, as illustrated in Listing 7:

Listing 7 - Implementing the delete function

    #include <ownership.h>

    #include <stdlib.h>


    struct X { 
      char *owner text; 
   };

    void x_delete(struct X *owner p) {
      if (p) {
        /*releasing the object*/ 
        free(p->text);
    
       /*releasing the memory*/ 
       free(p); 
     }
   }

   int main() {
      struct X \* owner pX = calloc( 1, sizeof \* pX);
      if (pX) {
       /*...*/;
       x_delete( pX); 
      }  
   }

    struct X {
        text: Option<Box<str>>,
    }
    fn main() {
        let pX = Box::new(X { text: None });
        // automatically dropped (freed) at end of scope
    }

For instance, this code is correct.

    #include <ownership.h> 
    #include <stdlib.h>

    struct X {
       char * owner text;
    };

    void x_delete(struct X * owner p)
    {
        if (p)
        {
           free(p->text);
           free(p);    
        }
    }

    int main() {   
       struct X * owner p = malloc(sizeof(struct X));
        
       p->text = malloc(10);

       free(p->text); //object text destroyed

       struct X x2 = {0};

       *p = x2; //x2 MOVED TO *p

       x_delete(p);   

       //no need to destroy x2
    }

    let p: Box<X> = Box::new(X { ... });

    let x2 = X { ... };

    // Moves x2 into the same memory as the first X.
    // The first X is automatically dropped as part of this assignment.
    // Also consumes x2 so x2 is not available any more.
    *p = x2;

    // Drops the X that was originally assigned to x2 and then moved into p.
    drop(p);

    // No need, nor is it possible, to destroy x2.

As I said I am not Rust specialist.

Also, in my understanding is that in Rust, sometimes a dynamic state is created when the object may or may not be moved.

In cake ownership this needs to me explicit ( and the destructor is not generated)

I also had a look at Rust in lifetime annotations. This concept may be necessary but I am avoiding it.

Consider this sample.

   struct X {  
     struct Y * pY;  
   };  
   struct Y {  
     char * owner name;  
   };  

Also (classic Rust sample)

    int * max(int * p1, int * p2) {  
      return *p1 > *p2 ? p1 : p2;
    }

    int main(){  
       int * p = NULL;
       int a  = 1;
      {
         int b = 2;
         p = max(&a,  &b);
      }
      printf("%d", *p);
    }

   int * p = NULL;
   int a  = 1;
   {
      int b = 2;
      p = max(&a,  &b);
   } //p cannot be used beyond this point*

`Box<T>` is the type of an owning pointer that uses the default global allocator, and `Box<T, A>` is the type of an owning pointer that uses an allocator of type `A`. The latter is unstable, ie it can only be used in nightly Rust.

(Also the fact that the latter changes the type means a large part of existing third-party code as well as a bunch of code in libstd itself becomes unusable if you want to use a type-level custom allocator because they only work with `Box<T>`. But that's a different discussion...)

>An object Y pointed by pY must live longer than object X.

Yes, the py field in Rust would use a reference type instead of a pointer, and the reference would need to have a lifetime annotation, and the compiler would work to prevent the situation you describe:

    struct X<'a> { py: &'a Y }

    let y = Y { ... };
    let x = X { py: &y };
    drop(y); // error: y is borrowed by x so it cannot be moved.

    let y: String = "a".to_owned();
    let x = &y;
    drop(y); // error: y is borrowed by x so it cannot be moved.
    do_something_with(x);

Let's say I have to objects on the heap. A and B. A have a "view" to B.

Then we put a prompt for the user. (or dynamic condition) "Which object do you want to delete first A or B?" Then user select B. How this can be checked at compile time?

Yes?

    if cond {
        drop(p)
    }
    // p may or may not be dropped here

    let p;
    if cond {
        p = something();
    }
    // p may or may not be set here

    int * owner p = malloc(sizeof(int));
    if (condition) 
       free(p);
    free(p); // error p may be initialized/moved.

    int * owner p = malloc(sizeof(int));
    if (condition) 
    { 
      free(p);
      p = 0;
    }
    free(p);

Here it is as a runnable snippet: https://godbolt.org/z/fc4Gfxrfd

    int main() {   
       struct X * owner p = malloc(sizeof(struct X));
        
       p->text = malloc(10);

       free(p->text); //object text destroyed

       //p->text is on uninitialized state. 
       //cannot be used (except assignment)

       struct X x2 = {0};

       *p = x2; //x2 MOVED TO *p

       x_delete(p);

The temporary solution, is the re-declare the malloc etc when compiling with cake and not complain withe the function signature difference only by owner qualifiers.

if this ownership were standard then gcc and mscv headers would have the qualifiers there enabled or not , but they would be there.

    #include <ownership.h> 
    #include <stdlib.h>
    #include <assert.h>
    #include <stdio.h>
    #include <string.h>

    struct node {
    char * owner text;
    struct node* owner next;
    };

    struct list {
    struct node * owner head;
    struct node * tail;
    };

    void list_append(struct list* list, struct node* owner node)
    {
    if (list->head == NULL) {
        list->head = node;
    }
    else {
        assert(list->tail->next == 0);
        list->tail->next = node; //ZERO OVERHEAD
    }
    list->tail = node;
    }

    void list_destroy(struct list* obj_owner list)
    {
    struct node * owner p = list->head;
    while (p) {
        struct node *  owner next = p->next;
        free(p->text); 
        free(p);
        p = next;
    }
    }

    void list_print(const struct list* list)
    {
    const struct node * p = list->head;
    while (p) {
        printf("%s ", p->text);
        p = p->next;
    }
    }

    int main()
    {
    struct list list = {};
    struct node  * owner p =  calloc(1, sizeof * p);
    
    if (p) {
        p->text = strdup("item1");
        list_append(&list, p);
    }

    list_print(&list);
    list_destroy(&list);
    }

On the other hand static analysis will catch the error at first compilation even on those almost never executed code.

    FILE* open_file(const char* p) {
        FILE* owner f = …
        return f;
    }

To fix we need to add qualifier owner at return type.

    FILE* owner open_file(const char* p) {
        FILE* owner f = …
        return f;
    }

https://thradams.com/cake/playground.html?code=I2luY2x1ZGUgP...

Ownership Feature Strategy (Inspired by stdbool.h)

If the compiler supports ownership checks and qualifiers such as _Owner, _View, _Obj_view, etc., it must define __STDC_OWNERSHIP__.

However, even if the compiler implements ownership, it is not active by default. The objective is to have a smooth transition allowing some files without checks. For instance, a thirty part code inside your project.

For instance, when compiling this file, even if the compiler supports ownership we don't have errors or warnings because the checks are not enabled by default.

    #include <stdlib.h>

    int main() {
      void \* p = malloc(1);
    }

    #include <ownership.h>
    #include <stdlib.h>

    int main() {
      void \* p = malloc(1); //error: missing owner qualifier
    }

Unless I misunderstood what OP meant about ownership composition.

Because this is C, the programmers can do wherever they want, but before it must do some negotiation with the static analysis.

If all you give me is half measures, then I’ll either just use plain old C/C++ or I’ll switch to a totally different language. Maybe one with a GC so I don’t have to please some ownership thingy.

Here is a blog post that explains this in more detail https://without.boats/blog/notes-on-a-smaller-rust/.

Not saying we shouldn't change anything.

I am saying that adding ownership is't the change that's needed, since you won't be able to convert most C code to that regime.

I've developed production code in C, C++, Rust, and several other languages. And while like pretty much everything, there are situations where it's not a good fit, I find that the solutions tend to be the most robust and require the least post release debugging in Rust. That's my personal experience. It's not hard data. And yes occasionally it's annoying to please the compiler, and if there were no trait constraints or borrow rules, those instances would be easier. But way more often in my experience the compiler complained because my initial solution had problems I didn't realize before. So for me, these situations have been about going from building it the way I wanted to -> compiler tells me I didn't consider an edge case -> changing the implementation and or design to account for that edge case. Also using one example, where Rust is notoriously hard and or un-ergonomic to use, and dismissing the entire language seems premature to me. For those that insist on learning Rust by implementing a linked list there is https://rust-unofficial.github.io/too-many-lists/.

Seems like you made a passive-aggressive presumption.

Pointer ownership could eliminate a class of bugs. And such an approach can be combined with run-time checks for bounds and signed overflow, and then you have a memory-safe C more or less (some minor pieces are still missing, but nothing essential),

I don't personally like Rust, I believe Rust achieves this. In Rust, if you don't use the unsafe escape hatch, then your bugs are at worst logic bugs. There won't be any kind of weirdness like that you got some math wrong in an array access and now all of a sudden an attacker can make your program execute arbitrary code.

On the other hand, this Cake thing just adds some ownership and when folks say it's problemmatic the first answer is "oh just tell it to ignore your function". That doesn't sound like memory safety to me. It's nowhere near Rust in that regard.

The experience is similar to changing a header file to use a const argument where previously the argument was non-const. This change will propagate everywhere.

I also think a similar experience is converting JavaScript to typescript. The type system will complain before it stabilizes.

As in, running nothing but memory-safety-ified C code down to the syscall boundary?

The cake source itself is moving to another experimental feature that is nullable types.

Similar of C# https://learn.microsoft.com/en-us/dotnet/csharp/nullable-ref...