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### 29.1 JIT Declarations

These are the relevant struct declarations that a C program should include to implement the interface:

    typedef enum
    {
      JIT_NOACTION = 0,
      JIT_REGISTER_FN,
      JIT_UNREGISTER_FN
    } jit_actions_t;

    struct jit_code_entry
    {
      struct jit_code_entry *next_entry;
      struct jit_code_entry *prev_entry;
      const char *symfile_addr;
      uint64_t symfile_size;
    };

    struct jit_descriptor
    {
      uint32_t version;
      /* This type should be jit_actions_t, but we use uint32_t
         to be explicit about the bitwidth.  */
      uint32_t action_flag;
      struct jit_code_entry *relevant_entry;
      struct jit_code_entry *first_entry;
    };

    /* GDB puts a breakpoint in this function.  */
    void __attribute__((noinline)) __jit_debug_register_code() { };

    /* Make sure to specify the version statically, because the
       debugger may check the version before we can set it.  */
    struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };

If the JIT is multi-threaded, then it is important that the JIT synchronize any modifications to this global data properly, which can easily be done by putting a global mutex around modifications to these structures.