[Buildroot] libstdc++ DSO missing

[Richard Ash]

On Sun, 11 Sep 2022 11:41:51 +0200
Alex <earthquake.de at freenet.de> wrote:

> Thank you for your detailed explanation.
> > On 09/09/2022 14:34, Alex wrote:  
> >> Hi,
> >>
> >> I intergrated my application to buildroot. Complie is successfull
> >> by when linking I get errors:
> >>
> >> x86_64-buildroot-linux-gnu/sysroot/usr/lib64/libstdc++.so.6: error
> >> adding symbols: DSO missing from command line  
> >
> > This error means that:
> > - the linker found a library with a DT_NEEDED dependency on 
> > libstdc++.so.6
> > - the linker found libstdc++.so.6
> > - the linker is missing symbols
> > - the linker found the missing symbols in libstdc++.so.6
> > - but the linker command line does not include libstdc++.so.6
> > - so the linker is not sure if the user actually intended to link
> > with libstdc++.so.6.
> > - so it refuses to link.
> >
> > Since libstdc++.so.6 is the C++ runtime library, this either mean
> > that:
> > - you are linking a C++ program with ld or gcc instead of g++  
> 
> Yap, outside of buildroot, linking calls the g++ but when linking
> inside buildroot,  calls the x86_64-buildroot-linux-gnu-ld,
> because $(LD) in the makefile is set to x86_64-buildroot-linux-gnu-ld 
> within buildroot.

I don't think it's ever been normal usage to use $(LD) when trying to
link anything involving dynamic linkage. As far as I'm aware, your
Makefile shouldn't be using $(LD) if you are linking dynamically. As
you are linking a C++ application, the link command should be using
$(CXX) (make doesn't seem to have a built in rule for linking C++, but
it's what I have always used and not had this sort of problem).
$(CXX) will be pointing to the correct g++, which will then call out to
the correct ld as required, with the correct options.

If you make this change to your Makefile you shouldn't need your kludge.

Richard
 
> Inside the package .mk file of the BUILD_CMDS calls make:
> 
> $(MAKE) $(TARGET_CONFIGURE_OPTS)  -C $(@D)
> 
> So (a kludge to test), i replaced in the Makefile
> $(LD)
> by
> $(HOST_DIR)/bin/x86_64-linux-g++
> Now linking is successfull...
> Is there a more "elegant" way to do this...? Not so a kludge like
> that, mean setting this within the mk file before calling the projekt
> make... And how to specifey $(CC) also to g++??
> 
> 
> > - you are linking a C program with a C++ library that requires 
> > libstdc++.so.6, in this case you may need -lstdc++ on the linker 
> > command line.
> >  
> >> Are libraries missing from buildroot environment?  
> >
> > No, only the linker command line is incorrect.
> >  
> >> Additional I get warnings that some .so files not found, but they
> >> are available in output/build/<Tool>/lib  
> >
> > The compiler will only search libraries in output/staging/lib or 
> > output/staging/usr/lib.
> > The package for <Tool> should install the libraries there, so that 
> > other programs can link with them. This is done by putting
> >
> > <TOOL>_INSTALL_STAGING = YES
> >
> > in its .mk file.  If <Tool> is a generic-package (and not a 
> > autotools/meson/cmake package), then you also need to manually
> > explain how to install libraries to $(STAGING_DIR)/lib:  
> 
> Indeed I forgot one of the .so to be  installed to staging. After
> adding this and append to the $(MAKE) call the
> LD_LIBRARY_PATH="$(@D)../<Tool>/lib" compile and linking is
> successfull.
> 
> >
> > https://nightly.buildroot.org/manual.html#_infrastructure_for_packages_with_specific_build_systems 
> >
> >  
> >> But I included this path by $(@D)/../<Tool>/lib  
> >
> > While it may work, this is a kludge.