libNiFpgaLv.so has wrong SONAME in ELF header?

[Thomas DeSilva]

I'm currently trying to get Google Test to work with a WPILib project so we can have tests integrated smoothly into our codebase (the rationale here could be a thread of its own, so let's not get into it). I've managed to get an executable compiled and linked, but I've been struggling to get the loader to cooperate. My procedure thus far:

1. Install qemu-user, the current FRC C++ toolchain, Eclipse, and the WPILib plugin on an Ubuntu machine.
2. Create a build configuration in Eclipse which links with both WPILib and gtest, with the test executable as the build artifact.
3. Build the executable.
4. Consolidate all relevant shared object files in one directory so that qemu's loader can find them.
5. Set up symlinks for the libraries that came with WPILib (the symlinks between different versions of libraries, e.g. libi2c.so -> libi2c.so.2, were created as regular files by the Eclipse plugin installer, so I wrote a script to remake them).
5. Run the executable using qemu-arm with a sufficiently large kernel version number and the loader path set to the directory containing the consolidated shared object files.

On the last step, qemu throws an error which reads, "src/eclipse/2017Steamworks/test/Test: error while loading shared libraries: libNiFpgaLv.so.13: cannot open shared object file: No such file or directory". I found it strange that it was trying to load that version of the library, as the one that WPILib comes with is 16.0.0, not 13. However, when I checked the ELF header of the library, I found that the SONAME doesn't match the filename:

$ readelf -d libNiFpgaLv.so.16.0.0 
Dynamic section at offset 0xc3a0 contains 30 entries:
  Tag        Type                         Name/Value
 0x00000001 (NEEDED)                     Shared library: [libNiFpga.so.13]
 0x00000001 (NEEDED)                     Shared library: [libstdc++.so.6]
 0x00000001 (NEEDED)                     Shared library: [librt.so.1]
 0x00000001 (NEEDED)                     Shared library: [libgcc_s.so.1]
 0x00000001 (NEEDED)                     Shared library: [libpthread.so.0]
 0x00000001 (NEEDED)                     Shared library: [libc.so.6]
 0x0000000e (SONAME)                     Library soname: [libNiFpgaLv.so.13]

This also seems to be the case for some other NI libraries, like NiFpga and NiRioSrv. Is this intentional? How does the RoboRIO's loader handle this without having the same failure I am?

[Peter Johnson]

Originally Posted by Thomas DeSilva

This also seems to be the case for some other NI libraries, like NiFpga and NiRioSrv. Is this intentional? How does the RoboRIO's loader handle this without having the same failure I am?

If you look in /usr/local/natinst/lib/ on the roboRIO, you'll find symlinks from the foo.13 versions to the foo.16.0.0 versions (e.g. libNiFpga.so.13 is symlinked to libNiFpga.so.16.0.0).

[Thomas DeSilva]

Originally Posted by Peter Johnson

If you look in /usr/local/natinst/lib/ on the roboRIO, you'll find symlinks from the foo.13 versions to the foo.16.0.0 versions (e.g. libNiFpga.so.13 is symlinked to libNiFpga.so.16.0.0).

Great, thanks. I'll have to poke around its file system on Monday and see if I can get this working.

[codedr]

It doesn't matter what the file name is, the runtime linker is going to want the library that the executable was built with that is embedded in the executable that calls itself libxxx.13.so by the name inbedded in the library file.

The name in the executable can be found with ldd or readelf.

[Thomas DeSilva]

I moved all the libraries from the RoboRIO into my library search path, which solved the issue in my original post. However, now I have a different problem:

symbol lookup error: /lib/libHALAthena.so: undefined symbol: _ZN5nFPGA16nFRC_2017_17_0_220g_currentTargetClassE

I searched all of the libraries I have for this symbol and found it in libFRC_NetworkCommunicationLV.so.17.0.0, but libHALAthena.so doesn't require it:

$ readelf -dW /usr/arm-frc-linux-gnueabi/lib/libHALAthena.so

Dynamic section at offset 0x42434 contains 37 entries:
  Tag        Type                         Name/Value
 0x00000001 (NEEDED)                     Shared library: [libFRC_NetworkCommunication.so.17]
 0x00000001 (NEEDED)                     Shared library: [libi2c.so.2]
 0x00000001 (NEEDED)                     Shared library: [libRoboRIO_FRC_ChipObject.so.17]
 0x00000001 (NEEDED)                     Shared library: [libspi.so.1]
 0x00000001 (NEEDED)                     Shared library: [libvisa.so]
 0x00000001 (NEEDED)                     Shared library: [libpthread.so.0]
 0x00000001 (NEEDED)                     Shared library: [librt.so.1]
 0x00000001 (NEEDED)                     Shared library: [libMathParser_gcc-4.4-arm_v3_0_NI.so]
 0x00000001 (NEEDED)                     Shared library: [libwpiutil.so]
 0x00000001 (NEEDED)                     Shared library: [libstdc++.so.6]
 0x00000001 (NEEDED)                     Shared library: [libm.so.6]
 0x00000001 (NEEDED)                     Shared library: [libgcc_s.so.1]
 0x00000001 (NEEDED)                     Shared library: [libc.so.6]
 0x0000000e (SONAME)                     Library soname: [libHALAthena.so]

$ readelf -sW wpilib/cpp/current/lib/libFRC_NetworkCommunication.so.17.0.0 | grep FPGA
    37: 00066948    41 OBJECT  WEAK   DEFAULT   12 _ZTS38NetCommRPC_getFPGAHardwareVersion_args
    45: 00067198    42 OBJECT  WEAK   DEFAULT   12 _ZTS39NetCommRPC_getFPGAHardwareVersion_pargs
    48: 0007ce80     8 OBJECT  WEAK   DEFAULT   18 _ZTI40NetCommRPC_getFPGAHardwareVersion_result
   233: 0006716c    44 OBJECT  WEAK   DEFAULT   12 _ZTS41NetCommRPC_getFPGAHardwareVersion_presult
   314: 0007ce68     8 OBJECT  WEAK   DEFAULT   18 _ZTI38NetCommRPC_getFPGAHardwareVersion_args
   317: 00066974    43 OBJECT  WEAK   DEFAULT   12 _ZTS40NetCommRPC_getFPGAHardwareVersion_result
   339: 0000d098    32 FUNC    GLOBAL DEFAULT   10 getFPGAHardwareVersion
   432: 0007d348     8 OBJECT  WEAK   DEFAULT   18 _ZTI39NetCommRPC_getFPGAHardwareVersion_pargs
   440: 0007c240     8 OBJECT  WEAK   DEFAULT   18 _ZTI11FPGAVersion
   449: 000657f0    14 OBJECT  WEAK   DEFAULT   12 _ZTS11FPGAVersion
   537: 0007d330     8 OBJECT  WEAK   DEFAULT   18 _ZTI41NetCommRPC_getFPGAHardwareVersion_presult

$ readelf -sW wpilib/cpp/current/lib/libFRC_NetworkCommunicationLV.so.17.0.0 | grep FPGA
     3: 00000000     0 OBJECT  GLOBAL DEFAULT  UND _ZN5nFPGA16nFRC_2017_17_0_220g_currentTargetClassE