linux - Does ldd also show dependencies of dependencies?

Question

I have a binary for which ldd shows an unexpected dependency und libicuuc (from "icu").

#ldd A
[...]
libxml2.so.2 => /usr/lib64/libxml2.so.2 (0x00007faaf9722000)
libicuuc.so.49 => /usr/lib64/libicuuc.so.49 (0x00007faaf5689000)

Since on this system libxml depends dynamically on libicuuc, it makes sense that ldd enventually ends up finding it, but is it expected that libicuuc also appears in the ldd output for A? Is there some command to retrieve only the libraries that are linked in as dependencies of dependencies?

Answer 1

ldd shows all libraries that it would need to load when starting the application or loading a shared library.

readelf -d shows only direct dependencies of the binary.

$ readelf -d /opt/google/chrome/chrome | grep NEEDED
 0x0000000000000001 (NEEDED)             Shared library: [libX11.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libXrandr.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libXrender.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libXss.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libXext.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [librt.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libdl.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libgobject-2.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libgthread-2.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libglib-2.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libgtk-x11-2.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libgdk-x11-2.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libatk-1.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libgdk_pixbuf-2.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libpangocairo-1.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libcairo.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libpango-1.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libfreetype.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libfontconfig.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libnss3.so]
 0x0000000000000001 (NEEDED)             Shared library: [libnssutil3.so]
 0x0000000000000001 (NEEDED)             Shared library: [libsmime3.so]
 0x0000000000000001 (NEEDED)             Shared library: [libplc4.so]
 0x0000000000000001 (NEEDED)             Shared library: [libnspr4.so]
 0x0000000000000001 (NEEDED)             Shared library: [libpthread.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libgconf-2.so.4]
 0x0000000000000001 (NEEDED)             Shared library: [libdbus-1.so.3]
 0x0000000000000001 (NEEDED)             Shared library: [libXcomposite.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libasound.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libXfixes.so.3]
 0x0000000000000001 (NEEDED)             Shared library: [libcups.so.2]
 0x0000000000000001 (NEEDED)             Shared library: [libgcrypt.so.11]
 0x0000000000000001 (NEEDED)             Shared library: [libbz2.so.1.0]
 0x0000000000000001 (NEEDED)             Shared library: [libexpat.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libudev.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libstdc++.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libgcc_s.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [ld-linux-x86-64.so.2]

$ ldd /opt/google/chrome/chrome
    linux-vdso.so.1 =>  (0x00007fff9d3ff000)
    libX11.so.6 => /lib64/libX11.so.6 (0x00007f93186dc000)
    libXrandr.so.2 => /lib64/libXrandr.so.2 (0x00007f93184d3000)
    libXrender.so.1 => /lib64/libXrender.so.1 (0x00007f93182c9000)
    libXss.so.1 => /lib64/libXss.so.1 (0x00007f93180c5000)
    libXext.so.6 => /lib64/libXext.so.6 (0x00007f9317eb2000)
    librt.so.1 => /lib64/librt.so.1 (0x00007f9317caa000)
    libdl.so.2 => /lib64/libdl.so.2 (0x00007f9317aa6000)
    libgobject-2.0.so.0 => /lib64/libgobject-2.0.so.0 (0x00007f9317858000)
    libgthread-2.0.so.0 => /lib64/libgthread-2.0.so.0 (0x00007f9317656000)
    libglib-2.0.so.0 => /lib64/libglib-2.0.so.0 (0x00007f9317336000)
    libgtk-x11-2.0.so.0 => /lib64/libgtk-x11-2.0.so.0 (0x00007f9316cbf000)
    libgdk-x11-2.0.so.0 => /lib64/libgdk-x11-2.0.so.0 (0x00007f9316a00000)
    libatk-1.0.so.0 => /lib64/libatk-1.0.so.0 (0x00007f93167de000)
    libgdk_pixbuf-2.0.so.0 => /lib64/libgdk_pixbuf-2.0.so.0 (0x00007f93165bb000)
    libpangocairo-1.0.so.0 => /lib64/libpangocairo-1.0.so.0 (0x00007f93163ae000)
    libcairo.so.2 => /lib64/libcairo.so.2 (0x00007f9316103000)
    libpango-1.0.so.0 => /lib64/libpango-1.0.so.0 (0x00007f9315eb7000)
    libfreetype.so.6 => /usr/lib64/freetype-freeworld/libfreetype.so.6 (0x00007f9315c15000)
    libfontconfig.so.1 => /lib64/libfontconfig.so.1 (0x00007f93159e0000)
    libnss3.so => /lib64/libnss3.so (0x00007f93156a4000)
    libnssutil3.so => /lib64/libnssutil3.so (0x00007f9315479000)
    libsmime3.so => /lib64/libsmime3.so (0x00007f931524c000)
    libplc4.so => /lib64/libplc4.so (0x00007f9315046000)
    libnspr4.so => /lib64/libnspr4.so (0x00007f9314e09000)
    libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f9314bed000)
    libgconf-2.so.4 => /lib64/libgconf-2.so.4 (0x00007f93149bc000)
    libdbus-1.so.3 => /lib64/libdbus-1.so.3 (0x00007f9314778000)
    libXcomposite.so.1 => /lib64/libXcomposite.so.1 (0x00007f9314575000)
    libasound.so.2 => /lib64/libasound.so.2 (0x00007f9314294000)
    libXfixes.so.3 => /lib64/libXfixes.so.3 (0x00007f931408e000)
    libcups.so.2 => /lib64/libcups.so.2 (0x00007f9313e33000)
    libgcrypt.so.11 => /lib64/libgcrypt.so.11 (0x00007f9313bba000)
    libbz2.so.1.0 => not found
    libexpat.so.1 => /lib64/libexpat.so.1 (0x00007f9313991000)
    libudev.so.0 => /lib64/libudev.so.0 (0x00007f9313782000)
    libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f931347f000)
    libm.so.6 => /lib64/libm.so.6 (0x00007f9313184000)
    libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f9312f6e000)
    libc.so.6 => /lib64/libc.so.6 (0x00007f9312bb7000)
    /lib64/ld-linux-x86-64.so.2 (0x0000003c7a000000)
    libxcb.so.1 => /lib64/libxcb.so.1 (0x00007f9312999000)
    libffi.so.5 => /lib64/libffi.so.5 (0x00007f9312790000)
    libgmodule-2.0.so.0 => /lib64/libgmodule-2.0.so.0 (0x00007f931258c000)
    libgio-2.0.so.0 => /lib64/libgio-2.0.so.0 (0x00007f931223f000)
    libpangoft2-1.0.so.0 => /lib64/libpangoft2-1.0.so.0 (0x00007f9312012000)
    libXinerama.so.1 => /lib64/libXinerama.so.1 (0x00007f9311e0f000)
    libXi.so.6 => /lib64/libXi.so.6 (0x00007f9311c00000)
    libXcursor.so.1 => /lib64/libXcursor.so.1 (0x00007f93119f4000)
    libXdamage.so.1 => /lib64/libXdamage.so.1 (0x00007f93117f1000)
    libpng15.so.15 => /lib64/libpng15.so.15 (0x00007f93115c7000)
    libpixman-1.so.0 => /lib64/libpixman-1.so.0 (0x00007f9311340000)
    libz.so.1 => /lib64/libz.so.1 (0x00007f9311129000)
    libplds4.so => /lib64/libplds4.so (0x00007f9310f24000)
    libdbus-glib-1.so.2 => /lib64/libdbus-glib-1.so.2 (0x00007f9310cfd000)
    libgssapi_krb5.so.2 => /lib64/libgssapi_krb5.so.2 (0x00007f9310ab8000)
    libkrb5.so.3 => /lib64/libkrb5.so.3 (0x00007f93107d3000)
    libk5crypto.so.3 => /lib64/libk5crypto.so.3 (0x00007f93105a8000)
    libcom_err.so.2 => /lib64/libcom_err.so.2 (0x00007f93103a3000)
    libgnutls.so.26 => /lib64/libgnutls.so.26 (0x00007f93100eb000)
    libgpg-error.so.0 => /lib64/libgpg-error.so.0 (0x00007f930fee7000)
    libavahi-common.so.3 => /lib64/libavahi-common.so.3 (0x00007f930fcd9000)
    libavahi-client.so.3 => /lib64/libavahi-client.so.3 (0x00007f930fac8000)
    libcrypt.so.1 => /lib64/libcrypt.so.1 (0x00007f930f891000)
    libXau.so.6 => /lib64/libXau.so.6 (0x00007f930f68c000)
    libselinux.so.1 => /lib64/libselinux.so.1 (0x00007f930f46b000)
    libresolv.so.2 => /lib64/libresolv.so.2 (0x00007f930f251000)
    libkrb5support.so.0 => /lib64/libkrb5support.so.0 (0x00007f930f046000)
    libkeyutils.so.1 => /lib64/libkeyutils.so.1 (0x00007f930ee42000)
    libtasn1.so.3 => /lib64/libtasn1.so.3 (0x00007f930ec31000)
    libp11-kit.so.0 => /lib64/libp11-kit.so.0 (0x00007f930ea1e000)
    libfreebl3.so => /lib64/libfreebl3.so (0x00007f930e7b3000)

Is there some command to retrieve only the libraries that are linked in as dependencies of dependencies?

You can do set difference of ldd and readelf -d outputs.