There arent any restricting semantics in Go that makes a pure go implementation of the runtime impossible.

go's void* http://golang.org/pkg/unsafe/#Pointer

go's syscall mmap function. (Pure Go) https://code.google.com/p/go/source/browse/src/pkg/syscall/z...

pure go pkg with more mmap functionality. http://godoc.org/launchpad.net/gommap

Go's runtime mmap function. (C) https://code.google.com/p/go/source/browse/src/pkg/runtime/s...

Go's base memory allocation function. https://code.google.com/p/go/source/browse/src/pkg/runtime/m...

Go functions body may be implemented as asm. The standard math pkg is a great example of this feature. http://golang.org/src/pkg/math/

Considering all of these features there isnt really a whole lot about Go's semantics that prohibit it from being used in many of the low level projects that are typically written in C/C++.