caustic-ld

A self-hosted static and dynamic linker for the Caustic toolchain, written entirely in Caustic.

Takes .o ELF object files produced by caustic-as and outputs standalone Linux x86_64 executables — no GCC or GNU ld required.

Build

# From the repo root:
make linker    # builds ./caustic-ld

Usage

# Single object:
./caustic-ld program.cst.s.o -o program

# Multi-object:
./caustic-ld main.cst.s.o lib.cst.s.o -o program

# Dynamic linking (libc):
./caustic-ld program.cst.s.o -lc -o program

# Custom base address:
./caustic-ld program.cst.s.o --base 0x600000 -o program

Full pipeline

./caustic main.cst              # compile to .s
./caustic-as main.cst.s         # assemble to .o
./caustic-ld main.cst.s.o -o main   # link to executable
./main

Features

• Static linking: single and multi-object, resolves all relocations (R_X86_64_PC32, R_X86_64_PLT32)
• Dynamic linking: -lc, -lm, etc. Generates PLT/GOT, .dynamic, .dynsym, .hash, .rela.plt, PT_INTERP
• Eager binding: all dynamic symbols resolved at startup (DT_BIND_NOW)
• _start stub: auto-generated entry point that calls main and exits via syscall
• ELF output: proper program headers, section layout, symbol table

Architecture

.o files → elf_reader.cst → linker.cst → elf_writer.cst → executable

File	Purpose
elf_reader.cst	Parses ELF object files (sections, symbols, relocations)
linker.cst	Symbol resolution, relocation, PLT/GOT generation, dynamic metadata
elf_writer.cst	Writes static or dynamic ELF executables
main.cst	CLI parsing and orchestration

Static ELF layout

ELF header
Program headers (2): PT_LOAD R+X, PT_LOAD R+W
.text        (code)
.rodata      (string literals)
.data        (initialized globals)
.symtab / .strtab

Dynamic ELF layout

ELF header
Program headers (4): PT_LOAD R+X, PT_LOAD R+W, PT_INTERP, PT_DYNAMIC
.interp      (/lib64/ld-linux-x86-64.so.2)
.hash        (ELF hash table)
.dynsym      (dynamic symbol table)
.dynstr      (dynamic string table)
.rela.plt    (PLT relocations)
.plt         (procedure linkage table)
.text        (code)
.rodata      (string literals)
.got.plt     (global offset table)
.dynamic     (dynamic linker metadata)
.data        (initialized globals)
.symtab / .strtab

Limitations

• x86_64 Linux only
• No shared library output (only executables)
• No debug info (DWARF) passthrough
• No weak symbols or symbol versioning