Real native machine code via mmap(PROT_EXEC). No exec(). No strings.
Raw x86_64 bytes: mov, add, sub, imul, cmp, je, jne, call, ret, jmp.
ack(3,4): 0.12ms JIT vs 1.5ms CPython vs 28ms interpreter
fib-rec(20): 0.16ms JIT vs 3.4ms CPython vs 40ms interpreter
Added cond support to JIT (cascaded comparisons → conditional jumps).
Fixed JIT cache: sentinel value prevents retry on unjittable functions.
System V AMD64 ABI: args in rdi/rsi/rdx, callee-saved r12-r15.
Tail calls use jmp (true TCO at machine code level).
691 lines of jit.c. 114 functional tests pass. All C tests pass.