Re: [Buildroot] libstdc++ DSO missing

[Alex <earthquake.de@freenet.de>]

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.

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.
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