(ddd.info)Patching

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9.3 Patching
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Using GDB, you can open your program's executable code (and the core
file) for both reading and writing.  This allows alterations to machine
code, such that you can intentionally patch your program's binary.  For
example, you might want to turn on internal debugging flags, or even to
make emergency repairs.

   Note that depending on your operating system, special preparation
steps, such as setting permissions, may be needed before you can change
executable files.

   To patch the binary, enable `Edit => GDB Settings => Writing into
executable and core files'.  This makes GDB open executable and core
files for both reading and writing.  If you have already loaded a file,
you must load it again (using `Edit => Open File' or `Edit => Open
Core'), for your new setting to take effect.

   Be sure to turn off `Writing into executable and core files' as soon
as possible, to prevent accidental alterations to machine code.