trassir / odrey

ODR Violations Checker

Odrey

- What?

A Python script to check your C++ compiled stuff for One Definition Rule violations.

- Why?

Because debugging ODRV is cumbersome, not always trivial and it's better to catch it at build-time rather than at run-time with sanitizers.
Sanitizers are awesome, though. Use sanitizers.
_{^{at least hand sanitizers}}

It should be noted, that this task could be better done within compiler or linker themselves, where code model is available for more scrutinized analysis. Ideally, we would like to have a compiler option, something like -Wodr and have violations reported before linking procedure. No known compiler does this.

- How?

//foo.cpp
char func(char c) { return c; }
//bar.cpp
char func(char) { return 'b'; }

add_library(foo STATIC foo.cpp)
add_library(bar STATIC bar.cpp)
target_link_libraries(app foo bar)

[6/6] Linking CXX executable app
multiple definitions of func(char):
  in file foo.cpp.o
  in file bar.cpp.o

- But, technically how?

By dumping symbols from compiled .os, archived .as and linked .so and ensuring that there are no symbols having same signature and different implementation.

- What's the catch?

• currently it is a proof of concept, not guaranteed to work for all cases
• doesn't catch everything, very likely to catch more than needed
• potentially slow on large binaries

- Whatever! I am convinced! Lets get started!

1. • if linux: pacman, yum, apt or even make install yourself Python 3.6+, readelf and c++filt (usually in binutils package)
   • if windows: get dumpbin.exe from Visual Studio accessible in PATH envvar (e.g. via vcvarsall.bat or VS Command Prompt)
2. get odr.py someplace where you can execute it
3. run odr.py object.o more/object.o and/libstatic.a and/even/libdynamic.so
4. meditate on the output and see if it uncovers something nasty

- Manually? Boring!

Best served hot and integrated with build system of your choice!

See odr.cmake for an example of integration with CMake.