Question

When developing a kernel module in Linux, using the C standard library isn’t allowed.
However, in case I need to use some common functionality like strcat(), where do I need to go to?

Answer 1

Whatever is not implemented in the Linux kernel, you have to implement yourself or borrow from another open source kernel module. However, you’ll find that strcat is implemented in the kernel.

See the kernel API documentation. Specifically the Basic C Library Functions section for your general question, and the String Manipulation section for your specific question about strcat.

You’ll want to include linux/string.h.

I don’t know why the kernel API documentation doesn’t actually show the header file that you have to include to get the function. But if you’re looking for something, you can restrict your search to /include/linux because that is where header files go if they have functions that are shared amongst different parts of the kernel.

Header files outside /include/linux contain definitions only for source files residing in the same directory as the header. The exception is /arch/.../include, which will contain architecture-specific headers instead of platform independent ones.