What's the purpose of the UD2 opcode in the Linux kernel?

Question

I have found the following fragment in the Linux kernel (not the corresponding C code though), somewhere during the start up phase. You can clearly see the 0F 0B

Answer 1

It's the BUG() macro from include/asm-i386/bug.h.

/*
 * Tell the user there is some problem.
 * The offending file and line are encoded after the "officially
 * undefined" opcode for parsing in the trap handler.
 */

#ifdef CONFIG_DEBUG_BUGVERBOSE
#define BUG()                           \
 __asm__ __volatile__(  "ud2\n"         \
                        "\t.word %c0\n" \
                        "\t.long %c1\n" \
                         : : "i" (__LINE__), "i" (__FILE__))

For example, the one at 0C05AF is for file with name at 0xC0274A86 and line number 117 (0x75).