As you said, there is no reason you cannot bootstrap in a high level language. Operating systems were written in Lisp at one time; they had device drivers, interrupts, etc.
My point is not that C is not used, but that there is no compelling technical reason to use C anywhere. The fact that Lisp and ML do not have standardized features for low-level operations is not really much of an argument. We could add those features, and we could do so with ease (CMUCL and SBCL already have low-level pointer operations and a form of inline assembly language); the only reason we do not is that nobody has time to rewrite billions of lines of C code, or perhaps more that nobody will spend the money to do such a thing. The existence of C at various levels of the software stack is a historical artifact, primarily a result of Unix having been written in C and OSes written in other languages having been marketed poorly.
The lesson is not that C is good for writing low-level code; the lesson is that technical features are not terribly important.
I would also point out that an OS is not just about interrupt handlers and device drivers. Most of an OS is high-level code that is connected to interrupt handlers and device drivers through an interface. Even if C were the best language in the world for writing low-level code, I would still question the use of C elsewhere (imagine, as an alternative, an OS that follows the design of Emacs -- a small core written in C, the rest written in Lisp).
My point is not that C is not used, but that there is no compelling technical reason to use C anywhere. The fact that Lisp and ML do not have standardized features for low-level operations is not really much of an argument. We could add those features, and we could do so with ease (CMUCL and SBCL already have low-level pointer operations and a form of inline assembly language); the only reason we do not is that nobody has time to rewrite billions of lines of C code, or perhaps more that nobody will spend the money to do such a thing. The existence of C at various levels of the software stack is a historical artifact, primarily a result of Unix having been written in C and OSes written in other languages having been marketed poorly.
The lesson is not that C is good for writing low-level code; the lesson is that technical features are not terribly important.
I would also point out that an OS is not just about interrupt handlers and device drivers. Most of an OS is high-level code that is connected to interrupt handlers and device drivers through an interface. Even if C were the best language in the world for writing low-level code, I would still question the use of C elsewhere (imagine, as an alternative, an OS that follows the design of Emacs -- a small core written in C, the rest written in Lisp).