Dear LJ Genie: I am in linker hell

[maradydd]

I'm building a C++ project for an unusual platform, and am having some confusing problems with my libstdc++. For some reason which I cannot fathom, I am getting an absurd number of "undefined reference to..." linker errors for symbols which are indeed undefined in libstdc++.a, but which are definitely defined in libc.a and libgcc.a. Yes, I am

Comments

[feonixrift]

First thought: Library paths.

[maradydd]

All as they're supposed to be. libstdc++.a and libc.a are in the same directory, and ld is complaining about an undefined reference to vsprintf, which is defined in libc.a. Cf. also earlier, rectified issue with libgcc.a.

[feonixrift]

Mixing C and C++ headers like that set off "here be complicated" flags, so I went looking for summaries, since my c++ is rusty.

This matches my impression of the munging involved: http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html

[maradydd]

The wacky thing is, this is a pure C++ project. I think something about the way libstdc++ was compiled for this platform requires me to manually link in some C libraries (see speculation below about an incomplete libstdc++.la). Cross-compiling is such a headache.

[tangaroa]

Try changing the order in which you link the files in the g++ command. As absurd as it sounds, that once worked for me.

[maradydd]

I've had that happen before with other projects, though usually what solves it is putting the libraries with the necessary dependencies first, and right now the order is -lgcc -lc -lstdc++. I'll try putting -lstdc++ first and see if that gets me anywhere. Will report shortly.

I am, however, noticing that libstdc++.la doesn't specify libc.a as a dependency ... wondering if that might have something to do with it.

[maradydd]

Well, for crying out loud, putting -lstdc++ first did it. Thanks!

[vatine]

The reason is that the linker doesn't record where it last saw any specific (not yet needed) function/variable, so libraries must be linked in "reverse" dependency order (that is, if object file A depends on obnject file B, they either have to be in the same archive OR object file A must be processed before object file B).

Ugh, the cruft the brain picks up over the years.

[maradydd]

Amen to that one.

[patrickwonders]

This reminds me of a question we used to have on our "grill the programmer" interview questions at Xerox: why might a library appear on a link line more than once?

Sunpro fixed it. Apparently gcc has not.

[allonymist]

Ha! I ran into this in 2007:
http://allonymist.livejournal.com/9639.html