How To Implement Closures?

As I understand, closures could be unboxed using a generated trampoline, like
mov rax, qword 12345678ABCDEFh ; 10 bytes function address
jmp rax ; 2 bytes
payload times N db 0 ; closure environment

Won't that mess code cache?

[2]: no overflow checking functions, other kind of unsafe functions (like atoi, shit like strftime), lack of ssize_t (that can hold everything size_t can + atleast 1 bit), lack of [s]size_t function that can hold the maximum value of size_t * CHAR_BIT, intptr_t/uintptr_t are optional and badly designed, lack of [u]intptr_t type that can hold the maximum value of intptr_t * CHAR_BIT, lack of a byte type that is atleast 1 bit instead of char (char is atleast 8 bit and can be more even if you have 8-bit bytes if the encoding is more than 8 bit)