1. tramp.c

struct cont {
  int (*func)(int);
};

int work(int x) {
  return x + 2;
}

int direct(int x) {
  return work(x);
}

int indirect(struct cont* f, int x) {
  return f->func(x);
}

2. tramp.s

_work:
0000000000000000  pushq  %rbp
0000000000000001	movq	%rsp, %rbp
0000000000000004	leal	2(%rdi), %eax
0000000000000007	popq	%rbp
0000000000000008	ret
0000000000000009	nopl	(%rax)
_direct:
0000000000000010	pushq	%rbp
0000000000000011	movq	%rsp, %rbp
0000000000000014	popq	%rbp
0000000000000015	jmpq	0x1a
000000000000001a	nopw	(%rax,%rax)
_indirect:
0000000000000020	pushq	%rbp
0000000000000021	movq	%rsp, %rbp
0000000000000024	movq	%rdi, %rax
0000000000000027	movl	%esi, %edi
0000000000000029	popq	%rbp
000000000000002a	jmpq	*(%rax)