stshndx

stshndx, or st_shndx, refers to the section index field in an ELF symbol table entry. In each symbol table entry, which includes fields such as st_name, st_value, st_size, st_info, st_other, and st_shndx, the st_shndx value indicates the section header table index with which the symbol is associated. The field is a 16-bit value and is interpreted by the linker and tools that process ELF objects.

A non-special, valid value of st_shndx is the index of a real section header in the object file’s section header table. In this case the symbol is defined in or associated with that section. There are several special values used to express particular meanings:

- SHN_UNDEF (0): the symbol is undefined in the current object; its definition is expected to come from another object during linking.

- SHN_ABS (0xFFF1): the symbol has an absolute value; it is not tied to any section.

- SHN_COMMON (0xFFF2): the symbol is a common symbol, a tentative definition that requires allocation.

- SHN_XINDEX (0xFFFF): indicates that the real section index does not fit in the 16-bit field and requires an extended index mechanism; the precise handling depends on the ABI and toolchain.

There are also reserved ranges, such as SHN_LORESERVE and SHN_HIRESERVE, that delimit values used for special purposes. In ordinary objects, st_shndx typically contains the index of the section where the symbol is defined; in undefined or special cases, it contains one of the reserved markers above. Understanding st_shndx is essential for interpreting symbol provenance during linking and for tools that inspect ELF binaries.