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From what I know, even though the common OS have parts written in other languages, the kernel is entirely written in C.
I want to know if it's feasible to write a Kernel in C++ and if not, what would be the drawbacks.
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Traditionally, the arguments against using C++ in kernel code have been: Portability: availability of C++ compilers for all intended target platforms. This is not really an issue any more. Cost of C++ language mechanisms such as RTTI and exceptions.
The C language was actually created to move the UNIX kernel code from assembly to a higher level language, which would do the same tasks with fewer lines of code. Oracle database development started in 1977, and its code was rewritten from assembly to C in 1983.
The kernel is written in the C programming language [c-language]. More precisely, the kernel is typically compiled with gcc [gcc] under -std=gnu11 [gcc-c-dialect-options]: the GNU dialect of ISO C11. clang [clang] is also supported, see docs on Building Linux with Clang/LLVM.
The kernel is written using GNU C and the GNU toolchain. While it adheres to the ISO C89 standard, it uses a number of extensions that are not featured in the standard. The kernel is a freestanding C environment, with no reliance on the standard C library, so some portions of the C standard are not supported.
This is covered explicitly in the OSDev Wiki.
Basically, you either have to implement runtime support for certain things (like RTTI, exceptions), or refrain from using them (leaving only a subset of C++ to be used).
Other than that, C++ is the more complex language, so you need to have a bit more competent developers that won't screw it up. Linus Torvalds hating C++ being purely coincidental, of course.
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