Determine Direct Shared Object Dependencies of a Linux Binary

Determine direct shared object dependencies of a Linux binary?

You can use readelf to explore the ELF headers. readelf -d will list the direct dependencies as NEEDED sections.

 $ readelf -d elfbin

Dynamic section at offset 0xe30 contains 22 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libssl.so.1.0.0]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000000c (INIT)               0x400520
 0x000000000000000d (FINI)               0x400758
 ...

How to know which shared object is used?

You should use the ldd utility. In the same environment you would load your executable (Same LD_LIBRARY_PATH, e.t.c.)

How to find all shared libraries actually used during execution in Linux?

You can use ltrace(1) for this:

$ PROG='ls -l'
# Collect call info
$ ltrace -o calls.txt -l '*' $PROG &> /dev/null
# Analyze collected data
$ cat calls.txt | sed -ne '/->/{ s/^\(.*\)->.*/\1/; p }' | sort -u
libacl.so.1
libcap.so.2
libc.so.6
libselinux.so.1
ls
# Compare with ldd
$ ldd /bin/ls | wc -l
10

How to list library dependencies of a non-native binary?

is there any way to get a list of the dynamically linked dependency for of a foreign binary

You can list direct dependencies of a binary easily enough:

readelf -d a.out | grep NEEDED

 0x0000000000000001 (NEEDED)             Shared library: [librt.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

I know of no way to recursively continue this to get the full list (as ldd does). You'll have to repeat the process for every NEEDED library by hand.

How to find which shared library exported which imported symbol in my binary?

So, for example how can I find the shared library which exports the function named foo or printf or anything in an efficient way?

You can run your program with env LD_DEBUG=bindings ./a.out. This will produce a lot of output, which you can grep for foo and printf.

Note that the answer to "which external symbol in my binary is dependent on which shared library" is "whichever library defines this symbol first".

So if today your binary depends on lifoo.so for foo and on libc.so.6 for printf, nothing stops you from running with a different libfoo.so tomorrow, and that different version of libfoo.so may define different symbols. If the new version of libfoo.so defines printf, that would cause the answer to your question for symbol printf to change from libc.so.6 to libfoo.so.

(solved) C++ Load one Shared Object with dependencies and access their functions

As a start, change the order of the arguments in the link-commands

g++ -g -shared -o libtest2.so -L. lib2.o -ltest1
g++ -g -shared -o libtest3.so -L. lib3.o -ltest1 -ltest2

Note: it's not necessary with every linker, but the newer gold linker only resolves "from-left-to-right". Also there's a -Wl,--no-undefined option, which is very useful to catch these error.

Then add rpath into these commands so that the shared objects find their dependencies run-time:

g++ -g -shared -o libtest2.so "-Wl,-rpath,${PWD}" -L. lib2.o -ltest1
g++ -g -shared -o libtest3.so "-Wl,-rpath,${PWD}" -L. lib3.o -ltest1 -ltest2

After linkage, readelf -d should show the RPATH like this:

$ readelf -d libtest3.so |head -n10

Dynamic section at offset 0xdd8 contains 28 entries:
 Tag        Type                 Name/Value
 0x0000000000000001 (NEEDED)     Shared library: [libtest1.so]
 0x0000000000000001 (NEEDED)     Shared library: [libtest2.so]
 0x0000000000000001 (NEEDED)     Shared library: [libstdc++.so.6]
 0x0000000000000001 (NEEDED)     Shared library: [libc.so.6]
 0x000000000000001d (RUNPATH)    Library runpath: [/home/projects/proba/CatMan]

(Also there is libtool to deal with shared libraries.)

Mind you, because of name-mangling, the following change should be performed (though it is compiler-specific)

- OpenSymbol(pHandle, "printBase");
+ OpenSymbol(pHandle, "_ZN4Base9printBaseEv");

Shared library on Linux does not contain reference to one of its dependencies

Your version of cc (or the link editor used by it) seem to default to -Wl,--as-neeeded. In this case, the command line order matters. If -lcpdf comes first, there are no references to its symbols yet, and so no dependency is created. -l arguments should come last:

cc -shared -fpic -I$JAVA_HOME/include I$JAVA_HOME/include/linux jcpdfwrapper.c -o libjcpdf.so -L. -lcpdf

How to show all shared libraries used by executables in Linux?

1. Use ldd to list shared libraries for each executable.
2. Cleanup the output
3. Sort, compute counts, sort by count

To find the answer for all executables in the "/bin" directory:

find /bin -type f -perm /a+x -exec ldd {} \; \
| grep so \
| sed -e '/^[^\t]/ d' \
| sed -e 's/\t//' \
| sed -e 's/.*=..//' \
| sed -e 's/ (0.*)//' \
| sort \
| uniq -c \
| sort -n

Change "/bin" above to "/" to search all directories.

Output (for just the /bin directory) will look something like this:

  1 /lib64/libexpat.so.0
  1 /lib64/libgcc_s.so.1
  1 /lib64/libnsl.so.1
  1 /lib64/libpcre.so.0
  1 /lib64/libproc-3.2.7.so
  1 /usr/lib64/libbeecrypt.so.6
  1 /usr/lib64/libbz2.so.1
  1 /usr/lib64/libelf.so.1
  1 /usr/lib64/libpopt.so.0
  1 /usr/lib64/librpm-4.4.so
  1 /usr/lib64/librpmdb-4.4.so
  1 /usr/lib64/librpmio-4.4.so
  1 /usr/lib64/libsqlite3.so.0
  1 /usr/lib64/libstdc++.so.6
  1 /usr/lib64/libz.so.1
  2 /lib64/libasound.so.2
  2 /lib64/libblkid.so.1
  2 /lib64/libdevmapper.so.1.02
  2 /lib64/libpam_misc.so.0
  2 /lib64/libpam.so.0
  2 /lib64/libuuid.so.1
  3 /lib64/libaudit.so.0
  3 /lib64/libcrypt.so.1
  3 /lib64/libdbus-1.so.3
  4 /lib64/libresolv.so.2
  4 /lib64/libtermcap.so.2
  5 /lib64/libacl.so.1
  5 /lib64/libattr.so.1
  5 /lib64/libcap.so.1
  6 /lib64/librt.so.1
  7 /lib64/libm.so.6
  9 /lib64/libpthread.so.0
 13 /lib64/libselinux.so.1
 13 /lib64/libsepol.so.1
 22 /lib64/libdl.so.2
 83 /lib64/ld-linux-x86-64.so.2
 83 /lib64/libc.so.6

Edit - Removed "grep -P"

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