Question about shared libraries

sebelk · 10-08-2010, 07:56 AM

Let's say that we have a program /bin/foo that is linked against /usr/lib/libfoo.so.

Let's say that /usr/lib/libfoo.so was compiled against /usr/lib/libsomething.so and /usr/lib/libsomeotherthing.so

How can I know if library is using dynamic loading?

I mean: how can I know if foo is only using functions from either /usr/lib/libsomeotherthing.so or /usr/lib/libsomething.so when it's needed (on demand)?

Thanks in advance!

rob.rice · 10-08-2010, 10:46 AM

ldd prints the shared libraries required by each program or shared library specified on the command line

sebelk · 10-08-2010, 11:33 AM

Quote:

Originally Posted by rob.rice

ldd prints the shared libraries required by each program or shared library specified on the command line

Thanks! I knew that!

But I'am interested of get libraries that use dynamic loading

Dark_Helmet · 10-08-2010, 12:11 PM

From the man page of ldd:

Quote:

ldd prints the shared libraries required by each program or shared library specified on the command line.

(emphasis added)

So, as an example:

Code:

$ ldd /bin/ls
	linux-gate.so.1 =>  (0xb7859000)
	librt.so.1 => /lib/tls/i686/cmov/librt.so.1 (0xb7837000)
	libselinux.so.1 => /lib/libselinux.so.1 (0xb781c000)
	libacl.so.1 => /lib/libacl.so.1 (0xb7813000)
	libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb76b9000)
	libpthread.so.0 => /lib/tls/i686/cmov/libpthread.so.0 (0xb76a0000)
	/lib/ld-linux.so.2 (0xb785a000)
	libdl.so.2 => /lib/tls/i686/cmov/libdl.so.2 (0xb769c000)
	libattr.so.1 => /lib/libattr.so.1 (0xb7696000)
$ ldd /lib/libattr.so.1
	linux-gate.so.1 =>  (0xb785f000)
	libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb76e6000)
	/lib/ld-linux.so.2 (0xb7860000)

Also, the naming convention of libraries is that *.so libraries are dynamically linked whereas *.a libraries are statically linked. However, the only way that I know of to verify that a library uses dynamic linking is to use ldd as shown above.