elf dynamic relocation

Symbol and string tables

• DT_SYMTAB → ElfW(Sym)* symbol table
• DT_SYMENT → sizeof(ElfW(Sym)), sanity check
• DT_STRTAB → char* string table
• DT_STRSZ → size of string table (optional sanity / bounds)
• DT_HASH → old SysV hash table (access the same data then symtab)
• DT_GNU_HASH → GNU hash table (access the same data then symtab)

Aditional part

• TLS
• constructor
• destructor

Access

REL

addend inside the section bytes (base + symbol_value)

• DT_REL → relocation table address
• DT_RELSZ → total size
• DT_RELENT → entry size

RELA

addend inside relocation table (base + symbol_value + addent)

• DT_RELA → relocation table address
• DT_RELASZ → total size
• DT_RELAENT→ entry size

JMPREL

plt entry

• DT_JMPREL → table for PLT relocations
• DT_PLTREL → type: DT_REL or DT_RELA (aarch64 and x86-64 use rela)
• DT_PLTRELSZ → size of the PLT relocation table
• DT_PLTGOT → GOT used by PLT code (Arch-specific usage)

PLT resolution mode

you can resolve every plt symbol at the start or put stub to resolve them at first use

OTHER

• DT_NEEDED (if you also handle dependencies)
• DT_VERSYM / DT_VERNEED* (if you want correct versioning later)

order of resolution

• Phase 1: only REL/RELA + basic PLT + NEEDED
• Phase 2: symbol versioning
• Phase 3: TLS, RELRO, IFUNC, etc.