“extern C”函数从 C++ 共享对象符号表中消失

Question

我有一个正在为一个项目创建的共享对象库，我遇到了一个奇怪的问题，即在最终库符号表中找不到我声明为“extern C”的函数。我将目标文件与函数链接到库中，但由于某种原因，它们不在符号表中。这发生在 Linux 和 OS X 上。我使用 g++ 进行链接和编译。

编辑： 链接时我没有收到任何链接器错误。图书馆链接很好。我可以说这些函数不在库中，因为我检查了符号表并且它们不存在。我用于链接的命令如下：

g++ -m64 -Wl,-O1 -Wl,-rpath,/usr/local/Trolltech/Qt-4.8.2/lib -shared -Wl,-soname,libQtCommercialChart.so.1 -o libQtCommercialChart.so.1.0.0 ../build/release/lib/chartdataset.o ../build/release/lib/chartpresenter.o ../build/release/lib/charttheme.o ../build/release/lib/domain.o ../build/release/lib/qchart.o ../build/release/lib/qchartview.o ../build/release/lib/qabstractseries.o ../build/release/lib/chartbackground.o ../build/release/lib/chartelement.o ../build/release/lib/scroller.o ../build/release/lib/chartlayout.o ../build/release/lib/versiontracker.o ../build/release/lib/axisanimation.o ../build/release/lib/xyanimation.o ../build/release/lib/pieanimation.o ../build/release/lib/piesliceanimation.o ../build/release/lib/splineanimation.o ../build/release/lib/baranimation.o ../build/release/lib/stackedbaranimation.o ../build/release/lib/percentbaranimation.o ../build/release/lib/abstractbaranimation.o ../build/release/lib/horizontalbaranimation.o ../build/release/lib/horizontalstackedbaranimation.o ../build/release/lib/horizontalpercentbaranimation.o ../build/release/lib/areachartitem.o ../build/release/lib/qareaseries.o ../build/release/lib/chartaxis.o ../build/release/lib/qabstractaxis.o ../build/release/lib/chartvalueaxisx.o ../build/release/lib/chartvalueaxisy.o ../build/release/lib/qvalueaxis.o ../build/release/lib/chartbarcategoryaxisx.o ../build/release/lib/chartbarcategoryaxisy.o ../build/release/lib/qbarcategoryaxis.o ../build/release/lib/chartcategoryaxisx.o ../build/release/lib/chartcategoryaxisy.o ../build/release/lib/qcategoryaxis.o ../build/release/lib/chartdatetimeaxisx.o ../build/release/lib/chartdatetimeaxisy.o ../build/release/lib/qdatetimeaxis.o ../build/release/lib/bar.o ../build/release/lib/abstractbarchartitem.o ../build/release/lib/qabstractbarseries.o ../build/release/lib/qbarset.o ../build/release/lib/qbarmodelmapper.o ../build/release/lib/qvbarmodelmapper.o ../build/release/lib/qhbarmodelmapper.o ../build/release/lib/qbarseries.o ../build/release/lib/barchartitem.o ../build/release/lib/qstackedbarseries.o ../build/release/lib/stackedbarchartitem.o ../build/release/lib/qpercentbarseries.o ../build/release/lib/percentbarchartitem.o ../build/release/lib/qhorizontalbarseries.o ../build/release/lib/horizontalbarchartitem.o ../build/release/lib/qhorizontalstackedbarseries.o ../build/release/lib/horizontalstackedbarchartitem.o ../build/release/lib/qhorizontalpercentbarseries.o ../build/release/lib/horizontalpercentbarchartitem.o ../build/release/lib/qlegend.o ../build/release/lib/legendmarker.o ../build/release/lib/legendlayout.o ../build/release/lib/linechartitem.o ../build/release/lib/qlineseries.o ../build/release/lib/qpieseries.o ../build/release/lib/piesliceitem.o ../build/release/lib/piechartitem.o ../build/release/lib/qpieslice.o ../build/release/lib/qpiemodelmapper.o ../build/release/lib/qvpiemodelmapper.o ../build/release/lib/qhpiemodelmapper.o ../build/release/lib/qscatterseries.o ../build/release/lib/scatterchartitem.o ../build/release/lib/qsplineseries.o ../build/release/lib/splinechartitem.o ../build/release/lib/xychart.o ../build/release/lib/qxyseries.o ../build/release/lib/qxymodelmapper.o ../build/release/lib/qvxymodelmapper.o ../build/release/lib/qhxymodelmapper.o   -L/usr/local/Trolltech/Qt-4.8.2/lib -L/tmp/qcharts/lib/release -Wl,-rpath,/tmp/qcharts/lib/release /home/thinkbox/Desktop/libs/lib/lm_new_pic.o -L/home/thinkbox/Desktop/libs/lib -llmgr_pic -lcrvs_pic -lsb_pic -lact_pic -llmgr_dongle_stub_pic -ldl -lFNPload_pic -lQtGui -L/usr/local/Trolltech/Qt-4.8.2/lib -L/usr/X11R6/lib64 -lQtCore -lpthread

未公开的代码位于文件 versiontracker.o 中。我无法直接显示代码，但它只是在与此类似的庄园中声明的函数：

extern "C"
{
VersionUtils::VersionTracker* AllocateVersion()
{
    return new VersionUtils::VersionTracker();
}
}

Answer 1

您的链接器优化选项-Wl,-O1 可能会丢弃未使用的代码。 IE。如果您的代码库本身不调用外部 C 函数，则链接器可能会在优化时将它们作为未使用的代码忽略。
试试-Wl,-O0 看看问题是否消失。如果是这样，链接器选项就是罪魁祸首。