Linkers, Loaders, Object Files, and Binary Instrumentation: ELF and Mach-O Internals, Relocations, PIC/PLT/GOT, Symbol Interposition, LTO, and BOLT Post-Link Optimization

Deep End Era. Engineering with Sankalp · Oct 29, 2026 · 1h 14m

What happens after the compiler finishes generating .o object files? We go inside ELF and Mach-O headers, static relocations, the architecture of ultra-fast linkers (lld and mold), dynamic linking (PIC, PLT, GOT, RELRO, and LDPRELOAD), scalable ThinLTO, and how Meta's BOLT rewrites production binaries using hardware branch profiles to cut instruction cache and TLB misses.

Chapters

00:00:00 Opening: The Mystery inside the Two-Hundred-Megabyte Binary

00:03:26 Why Separate Compilation Needs a Linker: What Is Inside a Relocatable .o Object File?

00:08:32 Inside ELF and Mach-O: The Dual View of…