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Undefined Symbol when compiled with -O2 only on Mac

Answer 1

A:

Note that the following is a guess, and I can't say for certain unless/until you provide the exact compiler flags you're using -- but Xcode defaults to setting -fvisibility=hidden, which would hide pretty much any symbol in your library, unless it's declared as visible.

You can do the same on Linux, but GCC's default is not to hide symbols.

You'll find more information here: http://gcc.gnu.org/wiki/Visibility

2009-05-05 15:12:34

I don't use XCode to compile but CMake on both OS.

claferri 2009-05-05 15:16:32

Answer 2

+1 A:

Here's a guess at a workaround: try building the library with the -fno-common flag. If you have multiple definitions of this variable, you'll need to add "extern" to all but one.

Lance Richardson 2009-05-05 15:41:47

I had some variable defined multiple times and using -fno-common was very helpfull to see that (in fact not in my part of the code so not obvious) but the funny thing is that it wasn't the variable that was undefined at first ... Seems it now compile with extern definition of those other variables. Thank you!

claferri 2009-05-05 15:50:26

in fact I still get the same error if I remove the -fno-common ...I don't get why it works on linux and not on mac ...

claferri 2009-05-07 09:04:43

My other thought was that it might be related to the order of the *.o files in the *.a archive. Could you post output from "nm -A mylib.a | grep the_symbol"? Perhaps moving the object file containing the definition after the object file containing the reference will help the linker do the right thing.

Lance Richardson 2009-05-07 14:23:37

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Undefined Symbol when compiled with -O2 only on Mac

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