From: cauldwell.thomas@nospicedham.gmail.com   
      
   I've written the following C++ code as an example:   
      
   #include   // puts   
      
   extern void LibFunc(void) noexcept(false);  // likely to throw an exception   
      
   void Func(void)   
   {   
       try   
       {   
           LibFunc();   
       }   
       catch (...)   
       {   
           std::puts("caught");   
       }   
   }   
      
   gets compiled to:   
      
   .LC0:   
           .string "caught"   
   Func():   
           push    rbx   
           call    LibFunc()   
           jmp     .L1   
           mov     rdi, rax   
           call    __cxa_begin_catch   
           mov     edi, OFFSET FLAT:.LC0   
           call    puts   
           call    __cxa_end_catch   
   .L1:   
           pop     rbx   
           ret   
           mov     rbx, rax   
           call    __cxa_end_catch   
           mov     rdi, rbx   
           call    _Unwind_Resume   
      
   There's a few things I don't understand here:   
   (1) Why does Func save and restore the RBX register if it never changes it? I   
   realise that RBX is callee-saved and so you must push it onto the stack before   
   altering it, but I don't see anywhere where it's altered.   
   (2)  If 'LibFunc' throws an exception, how does it know where to jump back to?   
   In normal circumstances if the function returned normally, it would jump back   
   to the 'jmp .L1' instruction, but instead it has to jump back to one   
   instruction after that. How    
   does it know what offset of the return address to jump back to?   
   (3) I don't know why those last four lines are there. They look like   
   unreachable code to me.   
      
   Can anyone enlighten me please?   
      
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