• Paper: mold: A Massively Parallel Linker

    From John R Levine@johnl@taugh.com to comp.compilers on Fri Aug 28 17:19:09 2026
    From Newsgroup: comp.compilers

    Despite being essential system software, linkers don't get much respect. (They've been around for 75 years and there's only one book on them, mine.) They've traditionally been pretty slow, but it turns out you can make them a lot faster by careful parallelization.

    Abstract
    Linking is a critical step in the software build process that combines compiled object files into a single executable or shared library. Despite decades of engineering effort, link times remain a significant bottleneck in the edit-compile-debug cycle, particularly for large C++ programs. Existing linkers exploit limited parallelism, leaving most CPU cores idle during linking. We present mold, a Unix/Linux linker that applies data parallelism systematically across the entire linking pipeline. We first analyze the architectural constraints that prevent existing linkers from scaling, including entangled symbol resolution and archive processing, and then show how a clean-slate design
    that decouples them overcomes these limitations. On large real-world programs, mold links multi-gigabyte debug binaries in at most a few seconds, and often in under a second. It is 2.4-16.1x faster than the state-of-the-art lld linker, and
    up to 112x faster than the traditional GNU ld. An ablation study shows that no single optimization dominates; the speedup comes from the cumulative effect of parallelizing all passes.

    https://arxiv.org/abs/2608.23228

    Regards,
    John Levine, johnl@taugh.com, Taughannock Networks, Trumansburg NY
    Please consider the environment before reading this e-mail. https://jl.ly
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