Qt 5.11.3 works fine, but Qt 5.12.1 throws LINKER errors

m3g1dd

On Windows 10, Qt 5.11.3 builds my application without any issue. However Qt 5.12.1, throws LINKER errors:

main.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) void __cdecl NetLibrary::registerNetLibraryQML(void)" (_imp?registerNetLibraryQML@NetLibrary@@YAXXZ) referenced in function main
debug\application.exe : fatal error LNK1120: 1 unresolved externals

my main.cpp is like:

#include "../netlib/netlib.h"

int main(int argc, char *argv[])
{
    // ...
    NetLibrary::registerNetLibraryQML();
    // ...
}

My netlib.h contains:

namespace NetLibrary {

NETLIBSHARED_EXPORT void registerNetLibraryQML();

}

And my netlib.cpp contains:

namespace NetLibrary {

NETLIBSHARED_EXPORT void registerNetLibraryQML()
{
    static bool registered = false;
    if (!registered) {
        qmlRegisterType<Netlib>("com.application.Application", 1, 0, "Netlib");
        registered = true;
    }
}

}

I wonder why Qt 5.11.3 has no linker issue, but Qt 5.12.1 runs into errors.

Christian Ehrlicher

So how to you link against the netlib library? Are you sure the netlib library is linked with the same compiler as Qt?

m3g1dd

This post is deleted!

m3g1dd

@Christian-Ehrlicher

The linking to net-library is done inside *.pro file:

win32:CONFIG(release, debug|release): LIBS += -L$$OUT_PWD/../netlib/release/ -lnetlib
else:win32:CONFIG(debug, debug|release): LIBS += -L$$OUT_PWD/../netlib/debug/ -lnetlib
else:unix: LIBS += -L$$OUT_PWD/../netlib/ -lnetlib

INCLUDEPATH += $$PWD/../netlib
DEPENDPATH += $$PWD/../netlib

m3g1dd

@Christian-Ehrlicher

The compile which I'm using is MSVC2017_64bit :

0_1552284678534_5763dfd5-db4b-4072-a483-eb3481b83aca-image.png

0_1552284745737_5357e532-9eb7-4db9-beac-bcf8f1db78e0-image.png

Christian Ehrlicher

MSVC needs the correct path instead -L and -l afaik
https://doc.qt.io/qt-5/qmake-variable-reference.html#libs

m3g1dd

@Christian-Ehrlicher

Thanks :) The strange point is that I have two more libraries which I'm linking against with the same approach without any issue. But only this net library is giving me troubles!

Christian Ehrlicher

Maybe the function is not properly exported? Maybe take a look at the exported function declarations with Dependency Walker - make sure the export string (_imp?registerNetLibraryQML@NetLibrary@@YAXXZ) shown there looks exactly the same.

m3g1dd

@Christian-Ehrlicher

Good idea :) I'm going to employ dependency walker tools

m3g1dd

@Christian-Ehrlicher

I double-checked my netlib DLL with dependency walker, I can see the export:

0_1552303570459_5fc43f6a-1a49-4307-b5b4-156b5e8b1a6c-image.png

Also, on my main.obj I can see the import:

0_1552303780368_7fcee3d7-1947-477a-8391-4ff3c54e5ef9-image.png

Christian Ehrlicher

I've no idea - does the linker really links against the import lib? Are other functions from within the library are resolved?

hskoglund

@m3g1dd While checking the netlib DLL is a good thing for avoiding failures when launching your application.exe (when the .dll is loaded), here the error occurs not when running the app, but when linking it, So the .dll is immaterial, you could instead check the netlib.lib file, that's what the linker is reading.

Dependency Walker isn't well suited for reading .lib files, but there's a tool in MSVC2017 called dumpbin, easiest is to start it from a Developer Command Prompt for VS 2017. To get the complete information, use the /linkermember switch, say like this:

dumpbin /linkermember netlib.lib

Then check in the list if that symbol is exported, it should be 2 of them, one __imp?registerNetLibraryQML@NetLibrary@@YAXXZ and one ?registerNetLibraryQML@NetLibrary@@YAXXZ

m3g1dd

@hskoglund

Thanks! I run the command on Developer Command Prompt for VS 2017 and I get the results, I can see both ?registerNetLibraryQML@NetLibrary@@YAXXZ and __imp_?registerNetLibraryQML@NetLibrary@@YAXXZ expressions:

C:\Users\me\repos\build-application-Desktop_Qt_5_12_1_MSVC2017_64bit-Debug\netlib\debug>dumpbin /linkermember netlib.lib
Microsoft (R) COFF/PE Dumper Version 14.15.26730.0
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file netlib.lib

File Type: LIBRARY

Archive member name at 8: /
FFFFFFFF time/date
         uid
         gid
       0 mode
     C3D size
correct header end

    69 public symbols

     190A __IMPORT_DESCRIPTOR_netlib
     1B30 __NULL_IMPORT_DESCRIPTOR
     1C66 netlib_NULL_THUNK_DATA
     2878 ?registerNetLibraryQML@NetLibrary@@YAXXZ
     2878 __imp_?registerNetLibraryQML@NetLibrary@@YAXXZ
     2E0C ?tr@Netlib@@SA?AVQString@@PEBD0H@Z
     2E0C __imp_?tr@Netlib@@SA?AVQString@@PEBD0H@Z
     2E8A ?trUtf8@Netlib@@SA?AVQString@@PEBD0H@Z
     2E8A __imp_?trUtf8@Netlib@@SA?AVQString@@PEBD0H@Z
     1DBE ??0Netlib@@QEAA@XZ
     1DBE __imp_??0Netlib@@QEAA@XZ
     1E2C ??1Netlib@@UEAA@XZ
     1E2C __imp_??1Netlib@@UEAA@XZ
     1F06 ?agentDiscover@Netlib@@QEAAXXZ
     1F06 __imp_?agentDiscover@Netlib@@QEAAXXZ
     1FFA ?agentSlice@Netlib@@QEAA_NAEBVQUrl@@AEBVQString@@V3@222@Z
     1FFA __imp_?agentSlice@Netlib@@QEAA_NAEBVQUrl@@AEBVQString@@V3@222@Z
     210E ?discoveryInProgress@Netlib@@QEBA_NXZ
     210E __imp_?discoveryInProgress@Netlib@@QEBA_NXZ
     28FC ?setDiscoveryInProgress@Netlib@@QEAAX_N@Z
     28FC __imp_?setDiscoveryInProgress@Netlib@@QEAAX_N@Z
     2C7E ?slicingInProgress@Netlib@@QEBA_NXZ
     2C7E __imp_?slicingInProgress@Netlib@@QEBA_NXZ
     2A82 ?setSlicingInProgress@Netlib@@QEAAX_N@Z
     2A82 __imp_?setSlicingInProgress@Netlib@@QEAAX_N@Z
     2530 ?layerID@Netlib@@QEBA?AVQString@@XZ
     2530 __imp_?layerID@Netlib@@QEBA?AVQString@@XZ
     2982 ?setLayerID@Netlib@@QEAAXVQString@@@Z
     2982 __imp_?setLayerID@Netlib@@QEAAXVQString@@@Z
     2B82 ?slicingDone@Netlib@@QEBA_NXZ
     2B82 __imp_?slicingDone@Netlib@@QEBA_NXZ
     2A04 ?setSlicingDone@Netlib@@QEAAX_N@Z
     2A04 __imp_?setSlicingDone@Netlib@@QEAAX_N@Z
     24BE ?init@Netlib@@AEAAXXZ
     24BE __imp_?init@Netlib@@AEAAXXZ
     22AA ?getOsName@Netlib@@AEAA?AVQString@@XZ
     22AA __imp_?getOsName@Netlib@@AEAA?AVQString@@XZ
     2090 ?discoveryFinished@Netlib@@AEAAXXZ
     2090 __imp_?discoveryFinished@Netlib@@AEAAXXZ
     2B06 ?slicerFinished@Netlib@@AEAAXXZ
     2B06 __imp_?slicerFinished@Netlib@@AEAAXXZ
     1F80 ?agentLogReady@Netlib@@AEAAXXZ
     1F80 __imp_?agentLogReady@Netlib@@AEAAXXZ
     2430 ?handleSlicingInProgressChanged@Netlib@@AEAAX_N@Z
     2430 __imp_?handleSlicingInProgressChanged@Netlib@@AEAAX_N@Z
     232C ?getSlicerProgress@Netlib@@AEAAXXZ
     232C __imp_?getSlicerProgress@Netlib@@AEAAXXZ
     23AA ?getSlicerProgressFinished@Netlib@@AEAAXXZ
     23AA __imp_?getSlicerProgressFinished@Netlib@@AEAAXXZ
     1E9A __imp_??_7Netlib@@6B@
     2636 ?metaObject@Netlib@@UEBAPEBUQMetaObject@@XZ
     2636 __imp_?metaObject@Netlib@@UEBAPEBUQMetaObject@@XZ
     2752 ?qt_metacast@Netlib@@UEAAPEAXPEBD@Z
     2752 __imp_?qt_metacast@Netlib@@UEAAPEAXPEBD@Z
     26BE ?qt_metacall@Netlib@@UEAAHW4Call@QMetaObject@@HPEAPEAX@Z
     26BE __imp_?qt_metacall@Netlib@@UEAAHW4Call@QMetaObject@@HPEAPEAX@Z
     27D2 ?qt_static_metacall@Netlib@@CAXPEAVQObject@@W4Call@QMetaObject@@HPEAPEAX@Z
     27D2 __imp_?qt_static_metacall@Netlib@@CAXPEAVQObject@@W4Call@QMetaObject@@HPEAPEAX@Z
     2190 ?discoveryInProgressChanged@Netlib@@QEAAX_N@Z
     2190 __imp_?discoveryInProgressChanged@Netlib@@QEAAX_N@Z
     221A ?discoveryResultChanged@Netlib@@QEAAXVQJsonArray@@@Z
     221A __imp_?discoveryResultChanged@Netlib@@QEAAXVQJsonArray@@@Z
     2CFE ?slicingInProgressChanged@Netlib@@QEAAX_N@Z
     2CFE __imp_?slicingInProgressChanged@Netlib@@QEAAX_N@Z
     25B0 ?layerIDChanged@Netlib@@QEAAXVQString@@@Z
     25B0 __imp_?layerIDChanged@Netlib@@QEAAXVQString@@@Z
     2BFC ?slicingDoneChanged@Netlib@@QEAAX_N@Z
     2BFC __imp_?slicingDoneChanged@Netlib@@QEAAX_N@Z
     2D86 __imp_?staticMetaObject@Netlib@@2UQMetaObject@@B

Archive member name at C82: /
FFFFFFFF time/date
         uid
         gid
       0 mode
     C4B size
correct header end

    37 offsets

        1     190A
        2     1B30
        3     1C66
        4     2878
        5     2E0C
        6     2E8A
        7     1DBE
        8     1E2C
        9     1F06
        A     1FFA
        B     210E
        C     28FC
        D     2C7E
        E     2A82
        F     2530
       10     2982
       11     2B82
       12     2A04
       13     24BE
       14     22AA
       15     2090
       16     2B06
       17     1F80
       18     2430
       19     232C
       1A     23AA
       1B     1E9A
       1C     2636
       1D     2752
       1E     26BE
       1F     27D2
       20     2190
       21     221A
       22     2CFE
       23     25B0
       24     2BFC
       25     2D86

    69 public symbols

        7 ??0Netlib@@QEAA@XZ
        8 ??1Netlib@@UEAA@XZ
        9 ?agentDiscover@Netlib@@QEAAXXZ
       17 ?agentLogReady@Netlib@@AEAAXXZ
        A ?agentSlice@Netlib@@QEAA_NAEBVQUrl@@AEBVQString@@V3@222@Z
       15 ?discoveryFinished@Netlib@@AEAAXXZ
        B ?discoveryInProgress@Netlib@@QEBA_NXZ
       20 ?discoveryInProgressChanged@Netlib@@QEAAX_N@Z
       21 ?discoveryResultChanged@Netlib@@QEAAXVQJsonArray@@@Z
       14 ?getOsName@Netlib@@AEAA?AVQString@@XZ
       19 ?getSlicerProgress@Netlib@@AEAAXXZ
       1A ?getSlicerProgressFinished@Netlib@@AEAAXXZ
       18 ?handleSlicingInProgressChanged@Netlib@@AEAAX_N@Z
       13 ?init@Netlib@@AEAAXXZ
        F ?layerID@Netlib@@QEBA?AVQString@@XZ
       23 ?layerIDChanged@Netlib@@QEAAXVQString@@@Z
       1C ?metaObject@Netlib@@UEBAPEBUQMetaObject@@XZ
       1E ?qt_metacall@Netlib@@UEAAHW4Call@QMetaObject@@HPEAPEAX@Z
       1D ?qt_metacast@Netlib@@UEAAPEAXPEBD@Z
       1F ?qt_static_metacall@Netlib@@CAXPEAVQObject@@W4Call@QMetaObject@@HPEAPEAX@Z
        4 ?registerNetLibraryQML@NetLibrary@@YAXXZ
        C ?setDiscoveryInProgress@Netlib@@QEAAX_N@Z
       10 ?setLayerID@Netlib@@QEAAXVQString@@@Z
       12 ?setSlicingDone@Netlib@@QEAAX_N@Z
        E ?setSlicingInProgress@Netlib@@QEAAX_N@Z
       16 ?slicerFinished@Netlib@@AEAAXXZ
       11 ?slicingDone@Netlib@@QEBA_NXZ
       24 ?slicingDoneChanged@Netlib@@QEAAX_N@Z
        D ?slicingInProgress@Netlib@@QEBA_NXZ
       22 ?slicingInProgressChanged@Netlib@@QEAAX_N@Z
        5 ?tr@Netlib@@SA?AVQString@@PEBD0H@Z
        6 ?trUtf8@Netlib@@SA?AVQString@@PEBD0H@Z
        1 __IMPORT_DESCRIPTOR_netlib
        2 __NULL_IMPORT_DESCRIPTOR
        7 __imp_??0Netlib@@QEAA@XZ
        8 __imp_??1Netlib@@UEAA@XZ
       1B __imp_??_7Netlib@@6B@
        9 __imp_?agentDiscover@Netlib@@QEAAXXZ
       17 __imp_?agentLogReady@Netlib@@AEAAXXZ
        A __imp_?agentSlice@Netlib@@QEAA_NAEBVQUrl@@AEBVQString@@V3@222@Z
       15 __imp_?discoveryFinished@Netlib@@AEAAXXZ
        B __imp_?discoveryInProgress@Netlib@@QEBA_NXZ
       20 __imp_?discoveryInProgressChanged@Netlib@@QEAAX_N@Z
       21 __imp_?discoveryResultChanged@Netlib@@QEAAXVQJsonArray@@@Z
       14 __imp_?getOsName@Netlib@@AEAA?AVQString@@XZ
       19 __imp_?getSlicerProgress@Netlib@@AEAAXXZ
       1A __imp_?getSlicerProgressFinished@Netlib@@AEAAXXZ
       18 __imp_?handleSlicingInProgressChanged@Netlib@@AEAAX_N@Z
       13 __imp_?init@Netlib@@AEAAXXZ
        F __imp_?layerID@Netlib@@QEBA?AVQString@@XZ
       23 __imp_?layerIDChanged@Netlib@@QEAAXVQString@@@Z
       1C __imp_?metaObject@Netlib@@UEBAPEBUQMetaObject@@XZ
       1E __imp_?qt_metacall@Netlib@@UEAAHW4Call@QMetaObject@@HPEAPEAX@Z
       1D __imp_?qt_metacast@Netlib@@UEAAPEAXPEBD@Z
       1F __imp_?qt_static_metacall@Netlib@@CAXPEAVQObject@@W4Call@QMetaObject@@HPEAPEAX@Z
        4 __imp_?registerNetLibraryQML@NetLibrary@@YAXXZ
        C __imp_?setDiscoveryInProgress@Netlib@@QEAAX_N@Z
       10 __imp_?setLayerID@Netlib@@QEAAXVQString@@@Z
       12 __imp_?setSlicingDone@Netlib@@QEAAX_N@Z
        E __imp_?setSlicingInProgress@Netlib@@QEAAX_N@Z
       16 __imp_?slicerFinished@Netlib@@AEAAXXZ
       11 __imp_?slicingDone@Netlib@@QEBA_NXZ
       24 __imp_?slicingDoneChanged@Netlib@@QEAAX_N@Z
        D __imp_?slicingInProgress@Netlib@@QEBA_NXZ
       22 __imp_?slicingInProgressChanged@Netlib@@QEAAX_N@Z
       25 __imp_?staticMetaObject@Netlib@@2UQMetaObject@@B
        5 __imp_?tr@Netlib@@SA?AVQString@@PEBD0H@Z
        6 __imp_?trUtf8@Netlib@@SA?AVQString@@PEBD0H@Z
        3 netlib_NULL_THUNK_DATA

  Summary

          C0 .debug$S
          14 .idata$2
          14 .idata$3
           8 .idata$4
           8 .idata$5
           C .idata$6

m3g1dd

@Christian-Ehrlicher

Thanks! Yes, other functions of netlib are linked fine. I will update if I figure out the cause :)

hskoglund

Hi, just to check, what version of MSVC did you use for Qt 5.11.3 (when the linking worked), was it MSVC 2017 32-bit or MSVC 2017 64-bit?

m3g1dd

@hskoglund

Hi! Thanks for follow up :)

For Qt 5.11.3 I'm using MSVC2017_64bit which works fine. My build directories are:

build-application-Desktop_Qt_5_11_3_MSVC2017_64bit-Debug
build-application-Desktop_Qt_5_11_3_MSVC2017_64bit-Release
build-application-Desktop_Qt_5_12_1_MSVC2017_64bit-Debug

m3g1dd

New observation: I installed Qt5.12.0 and my application compiles/links/runs just fine. I'm going to re-install Qt5.12.1 ... I have a feeling maybe re-installing it will resolve linker errors ... lets see ...

m3g1dd

I reinstalled Qt 5.12.1 but it still throws the above-mentioned linker error. So basically, my observation is:

On Windows, Qt 5.11.3 and 5.12.0 work fine
On Windows, Qt 5.12.1 throws linker error
On Linux openSUSE Leap 15, Qt 5.12.1 works fine

hskoglund

Hmm, just to check again: release builds and debug builds on 5.12.0 MSVC 2017 links fine and dandy, but the same linker throws a tantrum both for release and debug builds on 5.12.1 MSVC 2017.

Also, could do you a similar dumpbin on a 5.12.0 debug built netlib.lib as you did above for a 5.12.1 debug build?

m3g1dd

@hskoglund

Let me double-check everything again ... I'll give an update ...