Dynamic Runtime Binary Monkey Patching (ELF/glibc)
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I often find myself needing to do really odd and weird things
in order to avoid administrative overhead of 'fixing' a distro's
library, or installing multiple versions thereof.

Sometimes the actual task to be fixed is trivial, but it's difficult
to make the external library (or even binary) do what you want it
to do.

libmonkey will completely replace a function for you with another
function of your choosing.

The function must match the exact prototype of the old one, and should
return the same type of value as the old one.

Optionally you can obtain the machine code which formerly belonged
to the 'pristine' original function, for later analysis.

This currently only works on ia32/amd64 architectures with the ELF
format and linux/glibc (it's possible it can work on other platforms
supporting ELF, but I doubt that).

See the Makefile and test_inject.c for example usage


You can get libmonkey to output more verbose information by setting
LIBMONKEY_DEBUG in the environment. The number should be a numeric
value. The higher the value, the more information is displayed


- The physical code size of the old function must be at least 12 bytes
(for amd64 platforms) or 5 bytes (for i386).

- If the victim binary was compiled with optimizations, it is possible
that the compiler may have entirely inlined the function for various
invocations. This means that control is never transferred to the
victim's actual address.

- M. Nunberg