Problem with gcc linker

[Alex Chen]

I set the flag -Wl,-R/usr/local/lib in the link phase of g++ and 
everything works fine now.
Thanks very much for the help Mr. Freyn and Dr. Kirby.

Alex

On 4/17/2011 4:54 AM, Axel Freyn wrote:
> Hi Alex,
> On Sat, Apr 16, 2011 at 09:55:48PM -0700, Alex Chen wrote:
>> After I set the compiler flag, I get the following compilation error:
>> Building file: /home/Projects/Cache.cpp
>> Invoking: GCC C++ Compiler
>> g++  -I"/home/Projects/include" -O0 -g3 -Wall -c -fmessage-length=0
>> -Wno-pragmas -m64 -fPIC -R"/usr/local/lib" -MMD -MP -MF"Cache.d"
>> -MT"Cache.d" -o"Cache.o" "/home/Projects/Cache.cpp"
>> g++: unrecognized option '-R/usr/local/lib'
>> (Whether there is a space between -R and /usr/local/lib does not matter,
>> they all produce the error.)
>>
>> If I use that flag for the linker, I get a different linker error:
>> Building target: libC.so
>> Invoking: GCC C++ Linker
>> g++ -L"/home/alexchen/Projects/lib" -R/usr/local/lib -shared -o"libC.so"
>> ./Disk.o ./Cache.o -luuid -latomic_ops
>> g++: unrecognized option '-R/usr/local/lib'
>> Finished building target: libC.so
>>
>> By the way, I am using Eclipse C++ plug-in so the flag is set via the
>> project's compiler/linker 'Miscellaneous' setting.
> You passed the "-R" to the compiler, but you should pass it to the
> linker.
> Also in the second example: "g++" ist NOT the linker (it will call the
> linker "ld" itself).
> So to correct the problem: you have to tell the compiler that
> "-R/usr/local/lib" is an option for the linker. That is done using
> "-Wl,..."
> So,  the command
>
> g++  -I"/home/Projects/include" -O0 -g3 -Wall -c -fmessage-length=0 -Wno-pragmas -m64 -fPIC -Wl,-R"/usr/local/lib" -MMD -MP -MF"Cache.d"  -MT"Cache.d" -o"Cache.o" "/home/Projects/Cache.cpp"
>
> should work.
> (See also http://gcc.gnu.org/faq.html#rpath)
>
> Axel
>>
>> On 4/16/2011 8:54 PM, Alex Chen wrote:
>>> Thanks for the information, Dr. Kirby.
>>> Is that -R flag for the compiler or the linker?
>>> I thought the linker's -L flag will tell it to look for libraries there.  I
>>> guess it does not embed the path in the final library file.
>>>
>>>> The issue is that the run time linker does not know to look in
>>> /usr/local/lib for
>>>> libraries, so unless the path is hard-coded into the executable, the
>>> libraries
>>>> will not be found.
>>>>
>>>> Some programs are compiled in such a way they automatically look in
>>>> /usr/local/lib. You should find that by recompiling all your sources with
>>> the
>>>> compiler flag "-R /usr/local/lib" will work.
>>>>
>>>> Setting
>>>>
>>>> LD_LIBRARY_PATH=/usr/local/lib
>>>> export LD_LIBRARY_PATH
>>>>
>>>> will probably "solve" your problem, in that your code will probably find
>>> the
>>>> libraries. But it's not a very good solution.
>>>>
>>>> You can change the places the run time linker looks for libraries. You
>>> could
>>>> make it always look in /usr/local/lib, but such a change is a bad idea
>>> IMHO.
>>>> Dave