How do you identify what a call instruction calls when the name is not shown?

Read the target: a <name> is resolved from symbols, <name@PLT> is an external library call, and call *%reg is a function pointer you must inspect at runtime.

Named function:

call <strings_not_equal>

The disassembler resolved the name from the symbol table.

Address only:

call *%rax

This calls a function pointer — examine %rax at runtime:

(gdb) p/a $rax
(gdb) x/i $rax

PLT calls (external library):

call <sscanf@PLT>

The @PLT suffix means it goes through the Procedure Linkage Table to call a shared library function.

Examining an unknown function:

(gdb) disas 0x401234

Or set a breakpoint and step into it:

(gdb) break *0x401234
(gdb) run
(gdb) si
(gdb) disas

Go deeper:

• PIC in shared libraries — how a <name@PLT> call reaches a shared-library function via PLT/GOT
• Wikipedia: Dynamic linker — lazy binding resolves the real address on first call