On Linux (CentOS) I have occasionally used -Wl,--unresolved-symbols=ignore-in-object-files when building a test application that only depends on parts of some object files even though the full dependency would require a lot more object files to be included. The point is that I know by design any unresolved symbols are never encountered when running the test application (otherwise it should just crash).
On OS X, I found similar options -Wl,-undefined,suppress (or warning, dynamic_lookup),-flat_namespace which allowed me to build the binary, but it failed at run time complaining about dyld: Symbol not found: ... even though the missing symbols are never used during the run (the same application runs perfectly fine on CentOS).
Is there something else to force the application to run (till it crashes if ever an unresolved symbol is encountered) like on Linux?
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I have an application which uses a class Foo from an .so shared library. I've come across a problem where at runtime it prints
<appname>: symbol lookup error: <appname>: undefined symbol: <mangled_Foo_symbol_name>
Now, it turned out that the unmangled symbol was for the constructor of the class Foo, and the problem was simply that an old version of the library was loaded, which didn't contain Foo yet.
My question isn't about resolving the error (that's obviously to use the correct library), but why it appears at runtime instead of at time of load / startup.
The line of code causing the error just instantiates an object of class Foo, so I'm not using anything like dlopen here, at least not explicitly / to my knowledge.
In contrast, if I remove the whole library from the load search path, I get this error at startup:
<appname>: error while loading shared libraries: libname.so.2: cannot open shared object file: No such file or directory
When the wrong version of gcc / libstdc++ is on the load path, an error also appears at starup:
<appname>: /path/to/gcc-4.8.0/lib64/libstdc++.so.6: version `GLIBCXX_3.4.20' not found (required by <appname>)
This "fail fast" behavior is much more desirable, I don't want to run my application for quite awhile first, until I finally realize it's using the wrong library.
What causes the load error to appear at runtime and how can I make it appear immediately?
From the man page of ld.so:
ENVIRONMENT
LD_BIND_NOW (libc5; glibc since 2.1.1) If set to a nonempty string, causes the dynamic linker to resolve all symbols at program startup instead of deferring function call resolution to the point when they are first referenced. This is useful when using a debugger.
LD_WARN (ELF only)(glibc since 2.1.3) If set to a nonempty string, warn about unresolved symbols.
I think you can not statically link .so library. If you want to avoid load/run time errors you have to use all static libraries (.a). If you do not have static version of library and source then try to find some statifier. After googling I find few statifiers but do not know how do they work so leaving that part up to you.
I am trying to diagnose linker/runtime errors using setenv LD_BIND_NOW TRUE. When I run the executable with this option enabled, I get the error
lib/libmkl_intel_thread.so: error: symbol lookup error: undefined symbol: DftiFreeDescriptor (fatal)
However, if I then remove the LD_BIND_NOW environmental variable, the program executes just fine (until termination, whereupon it reports a memory corruption--though that might be unrelated).
So I am a bit confused: How does the program execute when it has a symbol lookup error? I thought it would have to terminate as the program is written in C++, not Java. (See here for reference.)
Also, does this error imply that my rpath is set incorrectly, or has the MKL so been built improperly? Is there a fix that can be achieved in bounded time?
Firstly, I thought you needed LD_BIND_NOW=1 (as opposed to TRUE, though that may be a synonym).
Secondly, although your application would not have linked had there been an unresolved symbol, is it possible you've done some form of shared library update so that one of the libraries used now uses a library in turn with an unresolved symbol? Or that it's using a different library to that with which it was linked?
Trying to track down a segfault somewhere in MPI, I got this error:
./mpitest: symbol lookup error: /usr/lib64/libstdc++.so.6: bàþ;# BC_
-------------------------------------------------------------------
mpirun has exited due to process rank 2 with PID 8729 on ...
First, I'm used to getting lookup errors when the process is loaded if the library path is wrong. But those all happen before the process starts executing. This happened in the middle of the output from the test. Shouldn't all symbols be resolved by the runtime loader before the process starts?
Second, that symbol looks like garbage. It's certainly not a normal mangled C++ symbol.
Is it possible for memory corruptions (since I am tracking a segfault, it's likely there's something like that going on) to corrupt symbols like this?
This was compiled with icpc 12.0.3 20110309 on a Linux 2.6.18-194.32.1.el5 x86_64 machine.
OpenMPI loads plugins as dynamic shared object at runtime when MPI_INIT is called. See this FAQ. Therefore symbol lookup happens at that time. So it looks to me that your OpenMPI's libmpi_cxx.so was built against a different libstdc++ than what is available or found at runtime. on the system.
You can either rebuild OpenMPI, or if the correct libstdc++ is somewhere on your system (not /usr/lib64/libstdc++.so.6), you can adjust your LD_LIBRARY_PATH. Also, try setting LD_DEBUG=files to see if you are in fact load 2 different libstdc++'s.
I have Core static library, a few Component static libraries that relays on the Core one, and then there is an App that links against both Core and Component libraries. My App can link both against Core and Component as long as Component don't uses classes from Core (App uses classes from Core).
I got the following error in both armv6 and armv7 versions. So my problem is not the very popular linking issue that everyone has.
ld: symbol(s) not found for architecture armv6
clang: error: linker command failed with exit code 1 (use -v to see invocation)
I added reference to Core in Component and even added it in "Link Binary With Libraries" which shouldn't be necessary for static lib.
Since I start having this issue I start doubting my design... It probably makes more sense in dynamically linking environment but still it should be doable in static one, especially since this already works under Windows with MSVC compilers.
Edit:
I made some progress! Although I still don't know where to go with it.
Here is my setup:
Core has a class cResourceManager that has a templated method GetResource<T>(int id)
Core also has class cResource
Component has class cMesh that inherits cResource
Here are some tests:
If I try from App to call rm->GetResource<cMesh>(...) I get the linking error
If I try from App to construct cMesh I get linking the linking error
If I try from App to call static method that will return new instance of cMesh I get the linking error
If I comment out the construction of cMesh but leave other member cMesh function calls the App links fine. I can even call delete mesh.
I have never seen anything like it!
If you remove the cMesh constructor, then you are then using the default (no argument, no body) cMesh constructor that is given to you. It almost sounds like there's a build error or missing code as a result of some code in your cMesh constructor and so the library isn't actually getting generated, and perhaps Xcode isn't reporting the error. Xcode is no good at reporting linker errors.
I would suggest looking at what symbols the linker says are missing and double-check that they are actually defined in your code. My guess is that you're using one of those symbols in your cMesh constructor. A lot of times with virtual base classes, you may forget to define and implement a method or two in a child class. Could be a result of missing a method based on your template, or your template isn't #included correctly. This could compile fine but result in linker errors like you're seeing.
If Xcode isn't showing you the full linker error, show the Log Navigator (Command ⌘+7), double-click the last "Build " entry, select the error, and then press the button on the far-right of the row that appears when selected. The symbols should be listed there. If not, it's time for xcodebuild in the Terminal.
If it's not that case, I'd be interested in seeing the results of whether or not the library is being built for the appropriate architecture, or maybe this can spur some progress:
In the Xcode Organizer Shift ⇧+Command ⌘+2, click Projects and find the path to the DerivedData for your project.
In the Terminal, navigate to that directory (cd ~/Library/Developer/Xcode/DerivedData/proj-<random value>/)
Remove (or move aside) the Build directory (rm -r Build)
In Xcode, try to build with the cMesh constructor present.
Find the Library product file (cd Build/Products/<scheme>-iphoneos)
Your compiled static libraries (<libname>.a) should be in this directory. If they're not there, they didn't build (unless you put your products elsewhere). If your libraries are there, let's confirm that they actually are getting built for the appropriate architecture. Run otool -vh <library>.a. You should see something like:
$ otool -vh libtesting.a
Archive : libtesting.a
libtesting.a(testing.o):
Mach header
magic cputype cpusubtype caps filetype ncmds sizeofcmds flags
MH_MAGIC ARM V7 0x00 OBJECT 3 1928 SUBSECTIONS_VIA_SYMBOLS
As you can see, my test library was built for ARMv7.
Make sure you are linking them in the correct order.
If Component depends on symbols in Core, then Component needs to be first in the link order, so the linker knows which symbols to look for in Core.
In MSVC the order doesn't matter, but in most other compiler suites it does.
I don't think Clang generates code for armv6, if you're targeting devices that old you still need to use GCC.
I'm compiling a trivial wxWidgets app on MacOS X 10.6 with XCode 3.2
The linker is return an error about the symbol _main being defined twice:
once in main.mm
once in the test_app.cpp file.
After I commented out the macro:
Implement_App(TestApp)
The error went away, compiled & linked and I was able to run the application.
I haven't found this anywhere so any ideas about this?
IMPLEMENT_APP is a macro used in wxWidgets to create an entry point to the program without worrying about whether the program will be compiled on Windows, Mac, *nix, or whatever. As a result of this, IMPLEMENT_APP has to define main (or its equivalent, such as WinMain).
You might find the IMPLEMENT_APP_NO_MAIN macro to be useful. Check the other IMPLEMENT_APP_XXX functions in wx/app.h, too.
This paragraph from the wxApp overview is a little helpful too:
Note the use of IMPLEMENT_APP(appClass), which allows wxWidgets to dynamically create an instance of the application object at the appropriate point in wxWidgets initialization. Previous versions of wxWidgets used to rely on the creation of a global application object, but this is no longer recommended, because required global initialization may not have been performed at application object construction time.