问题
I am compiling using arm-linux-gnueabi-g++ version 4.7.3.
I have the arm-linux-gnueabi libraries installed at location:
/usr/arm-linux-gnueabi/lib, it contains libdl.a, libdl.so, libdl.so.2, and libdl-2.19.so.
libdl.so links to libdl.so.2 which links to libdl-2.19.so.
I am trying to link against the dl library (see command string below), but I always get the undefined reference errors.
arm-linux-gnueabi-g++ -I. -I../ -I../Comms/Linux -Wall -DLINUX -fpic -o ../../work/MyProgram main.o
-L../../work -L/usr/arm-linux-gnueabi/lib -lComms -lConsole -lUtilities -ldl
../../work/libUtilities.so: undefined reference to `dlsym'
../../work/libUtilities.so: undefined reference to `dlopen'
collect2: error: ld returned 1 exit status
If I compile using g++ 4.8.2 using the following commend then my program compiles, links, and executes fine.
g++ -I. -I../ -I../Comms/Linux -Wall -DLINUX -fpic -o ../../work/MyProgram main.o
-L../../work -lComms -lConsole -lUtilities -ldl
Obviously it can't find the libdl.so library; I thought that by adding the path to the location of the appropriate library by using the -L flag would fix the problem, but it didn't.
What am I missing with the ARM compiler command?
回答1:
Well, I found the answer, I needed -Wl,--no-as-needed flag before the -ldl. I had run across this flag before I asked the question, but apparently mistyped it because it hadn't worked for me.
I don't understand why the flag is needed, but the code does finish linking now.
A SO user here says that it has to do with recent (2013 as of the user's post) versions of gcc linking to --as-needed.
来源：https://stackoverflow.com/questions/27607130/undefined-reference-to-dlsym-and-dlopen