Other than malloc/free does a program need the OS to provide anything else?

Question

I\'m working on designing the kernel (which I\'m going to actually call the \"core\" just to be different, but its basically the same) for an OS I\'m working on. The specifics o

Answer 1

malloc is generally implemented in the C runtime in userspace, relying on specific OS system calls to map in pages of virtual memory. The job of malloc and free is to manage those pages of memory, which are fixed in size (typically 4 KB, but sometimes bigger), and to slice and dice them into pieces that applications can use.

See, for example, the GNU libc implementation.

For a much simpler implementation, check out the MIT operating systems class from last year. Specifically, see the final lab handout, and take a look at lib/malloc.c. This code uses the operating system JOS developed in the class. The way it works is that it reads through the page tables (provided read-only by the OS), looking for unmapped virtual address ranges. It then uses the sys_page_alloc and sys_page_unmap system calls to map and unmap pages into the current process.