Rust 'dylib' for custom target

embedded
1

Hello, this is my first post on the rust forum. I normally don't make posts on forums but since there is (almost) nothing of examples for what i want to do and have no idea how to start.

So the goal is to load a dylib at runtime in my custom kernel. The dylib is meant as a module for my kernel.
That means that the finshed product can load an dylib execute a predefined function and access kernel functions and also other modules.

The problem is when i want to compile my module to the target (x86_64 baremetal) it says it doesn't support dylib as crate target.

If i am correct this is because i never defined how a dynamic library should work in my own kernel?
If so how do i fix this? Where do i start?

Just to be sure, am i in the correct category?

EDIT:
The crates with their dependencies:

  • kernel (bin)

    • kernel-core

  • example-module-1 (dylib)

    • kernel-core

  • example-module-2 (dylib)

    • kernel-core
    • example-module-1

  • kernel-core (lib)

The ideal solution would be that kernel-core is staticly linked in the kernel and modules acces it from there.

EDIT2: adding crate type to edit 1

2

Exactly, it depends on what binary format your kernel uses. There cannot be a general "dylib for bare metal".

As an example you could look at how they make Linux kernel modules in rust: https://github.com/fishinabarrel/linux-kernel-module-rust

3

The example you gave makes use of the crate type staticlib, i can't use this since it static links all the dependencies such as other modules. (core and alloc are already linked in the kernel itself so i would also like to avoid adding those to each module)

4

If you use bin as crate type for the kernel, no function are exported from it.

5

I have a 'core' crate that can be used by the modules and the kernel. I am going to edit my topic and put my crate structure there.

6

What is the crate-type of kernel? Does it have main.rs (bin) or lib.rs (lib)?

7

Oops should've put it in the edit... It is bin

8

Then the kernel binary won't export any symbols other than the start function. This means that any symbols in kernel-core won't be available for the kernel modules.

9

Oh you are right, but if i load the modules myself in i can map the kernel-core to the dylib modules no?

10

kernel-core is linked into the kernel, so no. That would only be possible if kernel-core were to be a dylib, but then kernel would need to be linked itself, requiring you to write your own bootloader or a stub that links the rest of the kernel.

11

Full re-edit, i looked somewhat more things up about dynamic link etc. I can make my own dynamic linker in my kernel that loads ELF files, i just need my rust compiled as an dylib so that i can feed it into my own dynamic linker.

12

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