linux.conf.au, January 2003
      PRINCIPLES: Fundamental Constraints

Kernel is written in GNU C & inline assembler (for arch specific code).
static inline int foo(void) { return -ENOMEM; }

Global address space.  No memory protection: you can destroy everything.
int *foo = NULL;
*foo = 1; /* BOOM! */

No libc in the kernel: only a small subset.
malloc(), strtoul(), strdup()

No floating point or MMX usage.
int x = foo * 2.5; /* BOOM! */