Introduction

lld, part of the LLVM family of projects, is a high-performance linker for the ELF, COFF, and Mach-O object formats. This page describes the now-completed project to use lld as FreeBSD's base system linker.

LLD in Base

As of 13, lld is now the default system linker on all supported architectures.

Prior to this, lld was in use on i386, amd64, arm*, aarch64, and riscv64*, with other architectures still using GNU BFD ld. For more information, see arch(7) in the manual for your particular FreeBSD version.

To forcibly build world and kernel with LLD and install LLD as /usr/bin/ld in pre-13 versions, add to /etc/src.conf: 

WITH_LLD_IS_LD=yes
WITH_LLD_BOOTSTRAP=yes

WITH_LLD_BOOTSTRAP=yes uses lld as the linker for building the FreeBSD world, and has no effect on the linker installed in /usr/bin/ld. WITH_LLD_IS_LD=yes installes lld as /usr/bin/ld, and has no effect on the linker used for building world.

Historical Issues

LLD patches

MIPS

ARM

Ports

A FreeBSD ports exp-run is tracked in PR214864.

Common issues in ports:

  1. Passing compiler flags, such as -fPIC, to the linker.

  2. lld has no built-in search paths (/lib, /usr/lib). Normally the linker is invoked from the compiler driver, which adds the library search paths. If lld is invoked directly then library search paths must be explicitly specified, with -L/lib -L/usr/lib.

  3. Shared library protected symbol preemption.
  4. lld does not have a built-in default output target. For the most common use of the linker (linking individual .o objects in to an executable or shared object) lld infers the target from the first object file. However, when the linker is used to convert an arbitrary binary file into an ELF object (via -r -b binary) lld must have the output target specified explicitly with -m.

Resources

CategoryHistorical CategoryProject

LLD (last edited 2022-02-10T03:13:39+0000 by KubilayKocak)