ld: library not found for - linker

Question

I'm hitting a linker error (compile time, not run time):
ld: library not found for -l:/usr/lib/libobjc.A.dylib
That's just the latest version of the error. I'm trying to link against /usr/lib/libobjc.A.dylib, and I want to hard-code the path; the library is guaranteed to exist at this path on the platform I'm on. And it does:
bhaller#lanois % ls -l /usr/lib/libobjc.A.dylib
-rwxr-xr-x 1 root wheel 859536 Jan 23 08:59 /usr/lib/libobjc.A.dylib
I have tried:
-L/usr/lib/ -llibobjc.A.dylib
-L/usr/lib/ -llibobjc.A
-l/usr/lib/libobjc.A.dylib
-l:/usr/lib/libobjc.A.dylib
In every case I get the same error, that ld couldn't find the library. But it's right there, and I'm giving the complete path to it! What am I missing??
Here's the full invocation, with a bunch of other cruft:
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -lto_library /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libLTO.dylib -dynamic -arch x86_64 -headerpad_max_install_names -macosx_version_min 10.10.0 -o QtSLiM.app/Contents/MacOS/QtSLiM -L/Users/bhaller/Desktop/QtSLiM QMAKE/QtSLiM/../core/ -L/Users/bhaller/Desktop/QtSLiM QMAKE/QtSLiM/../eidos/ -L/Users/bhaller/Desktop/QtSLiM QMAKE/QtSLiM/../treerec/tskit/ -L/Users/bhaller/Desktop/QtSLiM QMAKE/QtSLiM/../gsl/ -L/Users/bhaller/Desktop/QtSLiM QMAKE/QtSLiM/../eidos_zlib/ -syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -rpath #executable_path/Frameworks -rpath /Users/bhaller/Qt5.9.8/5.9.8/clang_64/lib main.o QtSLiMWindow.o QtSLiMAppDelegate.o QtSLiMWindow_glue.o QtSLiMChromosomeWidget.o QtSLiMExtras.o QtSLiMPopulationTable.o QtSLiMIndividualsWidget.o QtSLiMEidosPrettyprinter.o QtSLiMAbout.o QtSLiMPreferences.o QtSLiMSyntaxHighlighting.o QtSLiMFindRecipe.o QtSLiMHelpWindow.o QtSLiMScriptTextEdit.o QtSLiMEidosConsole.o QtSLiMEidosConsole_glue.o QtSLiMConsoleTextEdit.o QtSLiM_SLiMgui.o QtSLiMTablesDrawer.o QtSLiMFindPanel.o QtSLiMGraphView.o QtSLiMGraphView_FixationTimeHistogram.o QtSLiMGraphView_FrequencySpectra.o QtSLiMGraphView_LossTimeHistogram.o QtSLiMGraphView_PopulationVisualization.o QtSLiMGraphView_FitnessOverTime.o QtSLiMGraphView_FrequencyTrajectory.o QtSLiMHaplotypeManager.o QtSLiMHaplotypeOptions.o QtSLiMHaplotypeProgress.o QtSLiMVariableBrowser.o qrc_buttons.o qrc_icons.o qrc_recipes.o qrc_help.o moc_QtSLiMWindow.o moc_QtSLiMAppDelegate.o moc_QtSLiMChromosomeWidget.o moc_QtSLiMExtras.o moc_QtSLiMPopulationTable.o moc_QtSLiMIndividualsWidget.o moc_QtSLiMAbout.o moc_QtSLiMPreferences.o moc_QtSLiMSyntaxHighlighting.o moc_QtSLiMFindRecipe.o moc_QtSLiMHelpWindow.o moc_QtSLiMScriptTextEdit.o moc_QtSLiMEidosConsole.o moc_QtSLiMConsoleTextEdit.o moc_QtSLiMTablesDrawer.o moc_QtSLiMFindPanel.o moc_QtSLiMGraphView.o moc_QtSLiMGraphView_FixationTimeHistogram.o moc_QtSLiMGraphView_FrequencySpectra.o moc_QtSLiMGraphView_LossTimeHistogram.o moc_QtSLiMGraphView_PopulationVisualization.o moc_QtSLiMGraphView_FitnessOverTime.o moc_QtSLiMGraphView_FrequencyTrajectory.o moc_QtSLiMHaplotypeManager.o moc_QtSLiMHaplotypeOptions.o moc_QtSLiMHaplotypeProgress.o moc_QtSLiMVariableBrowser.o -lcore -leidos -ltskit -lgsl -leidos_zlib -l:/usr/lib/libobjc.A.dylib -framework QtOpenGL -framework QtWidgets -framework QtGui -framework QtCore -framework DiskArbitration -framework IOKit -framework OpenGL -framework AGL -lc++ -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/11.0.0/lib/darwin/libclang_rt.osx.a -F/Users/bhaller/Qt5.9.8/5.9.8/clang_64/lib
ld: library not found for -l:/usr/lib/libobjc.A.dylib
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[1]: *** [QtSLiM.app/Contents/MacOS/QtSLiM] Error 1
make: *** [sub-QtSLiM-make_first] Error 2
I feel like I must just be an idiot, but I can't see it. Help?

Answer 1

Your linkage command shows that your linker is the OS X linker. Refer to it's manual
with respect to the -l option:
-lx
This option tells the linker to search for libx.dylib or libx.a in the library search path.
If string x is of the form y.o, then that file is searched for in the same places, but
without prepending lib or appending .a or .dylib to the filename.
This will show you why all of:
-L/usr/lib/ -llibobjc.A.dylib
-L/usr/lib/ -llibobjc.A
-l/usr/lib/libobjc.A.dylib
-l:/usr/lib/libobjc.A.dylib
are wrong. In each of your attempts, where name is whatever you have typed after -l,
the linker will be directed to search for libname.dylib or libname.a. Of course
none of those files - e.g. liblibobjc.A.dylib.dylib,liblibobjc.A.dylib.a - exists
in /usr/lib/ or any of the other specified or default search directories, and
in the third and fourth attempts, libname.(dylib|a) resolves to strings that that
cannot even possibly be unqualified filenames.
Your final variation evidently wants to used -l:name in an attempt to make the linker
search precisely for name ( = /usr/lib/libobjc.A.dylib). However,
-l:name is an option for the GNU Binutils linker, (the default linker in Linux)
and as per the documentation, is not an option for the OS X linker. (Furthermore, that option of the Binutils linker
directs the linker to search in each directory for a file with the exact unqualified name name, which /usr/lib/libobjc.A.dylib
could not be).
To get the linker to locate libobjc.A.dylib in /usr/lib/ you require the option:
-lobjc.A
Consider for example the other -l options in your your linkage command:
-lcore -leidos -ltskit -lgsl -leidos_zlib
Before you try that however, I suggest that you check in /usr/lib for the existence
of a symbolic link:
libobjc -> libobjc.A
This would indicate that libobjc.A is the version of libobjc that your toolchain
is configured to select, and that the linkage option you require is simply:
-lobjc
The search option -L/usr/lib/ is in any case redundant, since /usr/lib/ is a default
linker search directory.