Why nm shows no symbols for /lib/i386-linux-gnu/libc.so.6?

It's probably got its regular symbols stripped and what's left is its dynamic symbols, which you can get with nm -D.

@PSkocik answered this. I just want to add more detail. There are two kinds of symbol sections in ELF: .symtab and .dynsym (see the Linux Standard Base Core Specification, a.k.a. LSB_5.0.0, for details). .symtab is for the linking step of the shared lib itself. Once linking is finished, the .symtab section is not needed anymore. The .dynsym section contains important symbols that are supposed to be searched by the dynamic linker at run time. nm by default only dumps symbols in the .symtab section.

LSB_5.0.0 Section 10.2.2.1, “ELF Section Types”, says a conforming shared lib should have either .symtab or .dynsym but not both. As part of the ABI library, libc is stripped out of the .symtab to be spec conforming.