dynsym

The dynsym is the dynamic symbol table of an ELF (Executable and Linkable Format) file, stored in the section named .dynsym. It contains symbols that may be resolved at load time or at runtime by the dynamic linker, such as imported functions from shared libraries or exported symbols from the object itself.

Each entry in dynsym is an Elf32_Sym or Elf64_Sym, depending on architecture. A symbol entry includes st_name (an index into the dynamic string table, .dynstr), st_value, st_size, st_info (binding and type), st_other (visibility), and st_shndx (the section index or a special value such as SHN_UNDEF). A symbol with st_shndx set to SHN_UNDEF represents an undefined reference to be resolved by the dynamic linker.

The actual symbol names are stored in the separate string table .dynstr; st_name points to the name’s offset within that table. Dynsym entries are used by the dynamic linker to resolve relocations (REL/RELA) and to support lazy binding through the procedure linkage table (PLT).

Dynsym is contrasted with the static symbol table .symtab, which is used by the linker at link time for statically linked binaries. Many dynamically linked executables and shared libraries may omit or strip .symtab, while dynsym is required for dynamic linking.

Tools such as readelf -s, nm -D, or objdump -t can display dynamic symbols from the .dynsym section. In modern ELF files, symbol versioning information may accompany dynsym data via separate sections (e.g., .gnu.version), but version numbers are not stored directly in the symbol entries themselves.