To stop program execution when the contents of an address is written to:
(dbx) stop modify &variable
Keep these points in mind when using stop modify:
The event occurs when a variable gets written to even if it is the same value.
The event occurs before the instruction that wrote to the variable is executed, although the new contents of the memory are preset by dbx by emulating the instruction.
You cannot use addresses of stack variables, for example, auto function local variables.