An old thread about the same problem: https://forum.dlang.org/thread/mmxwhdypncaeikknlpyq@forum.dlang.org

struct jmp_buf {
    byte[256] data;
}

jmp_buf my_jmp_buf;

extern(C) {
    int setjmp(ref jmp_buf env);
    void longjmp(ref jmp_buf env, int);
}

void
second() {
    writefln("second");
    // calling 'longjmp' results in a crash with '-m64'
    // it works with '-m32mscoff'
    longjmp(my_jmp_buf, 1);
}

void
first() {
    second();
    writefln("first");
}

void
main() {
    if (setjmp(my_jmp_buf)) {
        writefln("we longjmp-ed to here");
    }
    else {
        first();
    }
}

I also want to use '-betterC' (exceptions won't work).

SrMordred had already figured it (setjmp vs _setjmp(..., null)) out: https://forum.dlang.org/post/abrjmdvvlqdmmnpxcdzh@forum.dlang.org