gdb.info: Altering

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Altering Execution

Once you think you have found an error in your program, you might want
to find out for certain whether correcting the apparent error would
lead to correct results in the rest of the run.  You can find the
answer by experiment, using the GDB features for altering execution of
the program.
   For example, you can store new values into variables or memory
locations, give your program a signal, restart it at a different
address, or even return prematurely from a function.