What does jmp * (indirect jump) do and where does it appear?

The * means "indirect": jmp *addr reads the target address from memory (or a register) and jumps to whatever it finds there, rather than to a fixed label.

* jmp * reads its target from memory (table + index*8) or a register, then jumps there — the mechanism behind switch tables, function pointers, and vtable dispatch. *

# Direct: jump to fixed address
jmp .L_label

# Indirect: jump to address stored at [table + rdi*8]
jmp *.L4(,%rdi,8)

Breaking down jmp *.L4(,%rdi,8):

1. Compute address: .L4 + %rdi * 8
2. Read 8 bytes from that address — this is the target
3. Jump to the target

Where it appears:

• Switch statements — jump through a jump table
• Function pointers — call *%rax calls the function pointed to by %rax
• Virtual dispatch (C++) — call *offset(%rax) calls through vtable

Examine in GDB:

(gdb) x/a 0x402500

Shows the address stored at that location — the actual jump target.

Go deeper:

• Intel JMP reference — near absolute indirect forms (target from register or memory)
• Wikipedia: Branch table — how compilers lower dense switch statements to an indexed jump
• Wikipedia: Virtual method table — indirect dispatch through a table of function pointers