gcclibcnm

Why nm libc.so reports no symbols?

I've built a simple program like this:

g++ application.cpp -o application.exe

and then executed the command;

ldd application.exe
...
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 
...

I want to list all the symbols of the libc library:

nm /lib/x86_64-linux-gnu/libc.so.6
nm: /lib/x86_64-linux-gnu/libc.so.6: no symbols

nm --defined-only /lib/x86_64-linux-gnu/libc.so.6
nm: /lib/x86_64-linux-gnu/libc.so.6: no symbols

Why nm reports no symbols? If libc.so.6 is not a library, but some kind of a link to the actual library, then how can I find the actual library?

Solution

  • By default, nm reads the .symtab section in ELF objects, which is optional in non-relocatable objects. With the -D/--dynamic option, you can instruct nm to read the dynamic symbol table (which are the symbols actually used at run time). You may also want to use --with-symbol-versions because glibc uses symbol versioning extensively.

    Alternatively, you can use eu-readelf --symbols=.dynsym or objdump -Tw. (readelf -sDW does not include symbol versioning information.)