在FFI中使用ptr :: NonNull是否有效? [英] Is it valid to use ptr::NonNull in FFI?

问题描述

Rust具有 ptr::NonNull 类型表示非NULL指针.在FFI中使用这种类型是否安全?

Rust has the ptr::NonNull type that represents a non-NULL pointer. Is it safe to use this type in FFI?

是否保证具有相同的二进制表示形式(忽略非FFI上下文，例如Option优化)，对齐方式，将使用情况注册为*mut T?

Is it guaranteed to have same binary representation (ignoring non-FFI context such as Option optimizations), alignment, register usage as *mut T?

例如，我可以实现此接口吗?

For example, could I implement this interface:

void call_me_from_c(char *without_nulls) __attribute__((nonnull));

使用

extern "C" fn call_me_from_c(without_nulls: ptr::NonNull<c_char>)

我不希望它做任何事情(除了与NULL误用会导致UB之外)，但我希望该接口能够证明该功能不需要非NULL争论.

I don't expect this to do anything (apart from causing UB when misused with NULL ;), but I would like the interface to document that the function requires non-NULL arguments.

推荐答案

这取决于您使用的Rust版本.

It depends on what version of Rust you are compiling with.

NonNull 现在具有repr(transparent) ，因此只要包装类型是安全的，就可以在FFI中安全使用.

NonNull now has repr(transparent), so it is safe to use in FFI so long as the wrapped type is safe.

#[stable(feature = "nonnull", since = "1.25.0")]
#[repr(transparent)]
pub struct NonNull<T: ?Sized> {
    pointer: NonZero<*const T>,
}

在Rust 1.29之前

我不会不将其用于此类用途.主要原因是由于其定义:

Before Rust 1.29

I would not use it for such. The main reason is due to its definition:

#[stable(feature = "nonnull", since = "1.25.0")]
pub struct NonNull<T: ?Sized> {
    pointer: NonZero<*const T>,
}

更具体地说，我担心定义中的不是:

More specifically, I'm concerned about what's not in the definition: #[repr(transparent)] (emphasis mine):

具有这种表示形式的结构具有相同的布局和ABI 作为单个非零大小的字段.

Structs with this representation have the same layout and ABI as the single non-zero sized field.

由于将新类型放在FFI函数中，我经历了错误编译，因此repr(transparent)不只是学术练习.

I've experienced miscompilation due to putting newtypes in a FFI function that were solved by repr(transparent), so this isn't just an academic exercise.

这篇关于在FFI中使用ptr :: NonNull是否有效?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！