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This is strange because I was able to get the error below to go away by removing the reference to libm.
gcc -o example example.o -Wl -L/home/kensey/cdev/lib -L/usr/lib/x86_64-linux-gnu -lmysqlclient -lpthread -lz -L/usr/lib/x86_64-linux-gnu -lm -lrt -ldl -lcdev -L/home/kensey/www.tools/gplot-lib -lgplot -L/home/kensey/www.tools/gd1_3ret -lgd -lxml2 -lcurl
/usr/bin/ld: /home/kensey/www.tools/gplot-lib/libgplot.a(set.o): undefined reference to symbol 'floor@@GLIBC_2.2.5'
/usr/bin/ld: note: 'floor@@GLIBC_2.2.5' is defined in DSO /usr/lib/x86_64-linux-gnu/libm.so so try adding it to the linker command line
/usr/lib/x86_64-linux-gnu/libm.so: could not read symbols: Invalid operation
collect2: ld returned 1 exit status
So, if I remove the -lm part of the command, I do not get the error. However, I wonder if anyone knows as to why removing a reference to a library that is needed would fix this. How does the linker know which library to look in? Also - is there a way to query a built executable and say 'which library did you resolve the reference to 'floor'? obviously, there is something going on that I don't understand, and that bothers me...