On 09/12/2013 04:05 AM, Yue Lu wrote: > Honestly to say, I have copied them from function gnu_xfer_memory. But > I think, before reference a pointer, check whether it was a NULL seems > not a bad way :-).
We don't go around checking for NULL before _every_ pointer dereference. :-) NULL pointer checks are used when the function's semantics give special meaning to NULL, like for example, for optional parameters. If that's not the function's semantics, and you still may see a NULL pointer, then that tells there's actually a bug that triggered already elsewhere before the function in question was called. IOW, a NULL check in these cases is just masking out a bug in some caller. In some cases, we might add a gdb_assert to catch the bug in a nicer way instead of just crashing. I suspect that what may happen is that at some point it was possible for GDB to select a no-longer-existing-thread (though I can't see how in the current code), and then setting breakpoints, or other operations that require reading memory would crash. -- Pedro Alves
