Implement Relocation Processing

Fixing Up Addresses at Link Time

The compiler emits code with placeholder offsets for symbols not yet located. Relocation entries tell the linker: at offset X in section Y, add the runtime address of symbol Z using relocation type R.

How Relocation Works

For call foo when foo is in another object, the compiler emits a PC-relative displacement with addend 0. The linker sets displacement = addr(foo) - (addr(call site) + 4).

cCopy
Loading…

• PC-relative for position-independent code
• Absolute relocations for data pointers
• REL vs RELA: addend inline vs in relocation entry
• Linker reports undefined symbol if no definition found

Connecting to real compilers

Production compilers embed this step inside a longer pipeline. GCC flows through cpp, cc1, assembly, and ld; Clang uses the driver, Sema, LLVM IR passes, and a target backend. LLVM bitcode, JVM bytecode, and WASM are other familiar IRs at the same layer. The exercise isolates one pass so you can test it alone before chaining it to the next stage.

Why for this exercise

You will implement relocation processing that patches object file bytes. This exercise asks you to apply relocation formulas to machine code and data sections given symbol final addresses.