AddressSanitizer does not fully support swapcontext. 
Sometimes, swapcontext causes the entire shadow region (16T) 
to be written by asan-internal routines (e.g. __asan_handle_no_return)
because the location of the stack changes w/o asan noticing it.
This may cause the machine to die or hang for a long time. 

I am not at all sure if asan can fully support swapcontext, 
but we at least should collect more test cases.