Is Microsoft the only one that can write trusted unsafe code?

Question

I would like to write some unsafe C# code for the purpose of writing high-performance, low-level libraries.

But I don't quite understand the limitations of where that code can run.

Microsoft obviously writes libraries that use unsafe code, which are fully trusted. Is Microsoft the only one who can do that?

Answer 1

But I don't quite understand the limitations of where that code can run.

The unsafe code should be able to run anywhere were .NET can run.

Is Microsoft the only one who can do that?

Anybody can write the unsafe code. Though you should be careful cause there is a reason why it is called "unsafe" and you should fully understand what you are doing. The only "limitation" is that you need to add AllowUnsafeBlocks compiler option to the project using unsafe keyword.

Also note that with introduction of Span and Memory and corresponding APIs you should be able handle at least some high-performance scenarios without need for using unsafe directly.