Tool for Library Dependency

Question

I'm looking for the tool/command on Unix platform to detect the library dependencies of the .so and .o files.

I have already used the ldd/nm/truss, but I don't know the proper approach to detect library dependencies.

Answer 1

It depends on what exactly is meant by "detect library dependencies".

The ldd command works on shared libraries, not just on executables. It will display the dependencies of a shared library declared when the library was built:

$ ldd /usr/lib/libgtk-3.so
    linux-vdso.so.1 (0x00007ffff8fff000)
    libgdk-3.so.0 => /usr/lib/libgdk-3.so.0 (0x00007f43fcf47000)
    libgmodule-2.0.so.0 => /usr/lib/libgmodule-2.0.so.0 (0x00007f43fcd43000)
    libpangocairo-1.0.so.0 => /usr/lib/libpangocairo-1.0.so.0 (0x00007f43fcb36000)
    libX11.so.6 => /usr/lib/libX11.so.6 (0x00007f43fc7fc000)
...

A library can have undefined symbols that are obtained by linking with further libraries not declared as dependencies. You can use objdump -T or nm -D to show the dynamic symbols - undefined symbols (those that should come from other libraries) will show up as *UND*:

$ objdump -T /usr/lib/libgtk-3.so | head

/usr/lib/libgtk-3.so:     file format elf64-x86-64

DYNAMIC SYMBOL TABLE:
0000000000066e38 l    d  .init  0000000000000000              .init
0000000000000000      DF *UND*  0000000000000000              g_param_spec_object
0000000000000000      DF *UND*  0000000000000000              g_utf8_validate
0000000000000000      DF *UND*  0000000000000000              g_date_get_month
0000000000000000      DF *UND*  0000000000000000              g_bookmark_file_get_visited
0000000000000000      DF *UND*  0000000000000000              g_value_get_float

From these symbol names it should be possible to deduce undeclared library dependencies.

Libraries that use pkg-config or similar configuration mechanism sometimes fail to declare their dependencies at build-time, but declare the dependencies to pkg-config, relying on the library users to use the tool to get the dependencies. pkg-config --libs will list the dependencies in the format understood by the compiler:

$ pkg-config --libs gtk+-3.0
-lgtk-3 -lgdk-3 -latk-1.0 -lgio-2.0 -lpangocairo-1.0 -lgdk_pixbuf-2.0 -lcairo-gobject -lpango-1.0 -lcairo -lgobject-2.0 -lglib-2.0