lld 21.1.8 Release Notes — lld 21.1.8 documentation

# lld 21.1.8 Release Notes

## Introduction

This document contains the release notes for the lld linker, release 21.1.8. Here we describe the status of lld, including major improvements from the previous release. All lld releases may be downloaded from the LLVM releases web site.

## Non-comprehensive list of changes in this release

### ELF Improvements

- Added `-z dynamic-undefined-weak` to make undefined weak symbols dynamic when the dynamic symbol table is present. (#143831)

- For `-z undefs` (default for `-shared`), relocations referencing undefined strong symbols now behave like relocations referencing undefined weak symbols.

- `--why-live=<glob>` prints for each symbol matching `<glob>` a chain of items that kept it live during garbage collection. This is inspired by the Mach-O LLD feature of the same name.

- `--thinlto-distributor=` and `--thinlto-remote-compiler=` options are added to support Integrated Distributed ThinLTO. (#142757)

- Linker script `OVERLAY` descriptions now support virtual memory regions (e.g. `>region`) and `NOCROSSREFS`.

- When the last `PT_LOAD` segment is executable and includes BSS sections, its `p_memsz` member is now correct. (#139207)

- Spurious `ASSERT` errors before the layout converges are now fixed.

- For ARM and AArch64, `--xosegment` and `--no-xosegment` control whether to place executable-only and readable-executable sections in the same segment. The default option is `--no-xosegment`. (#132412)

- For AArch64, added support for the `SHF_AARCH64_PURECODE` section flag, which indicates that the section only contains program code and no data. An output section will only have this flag set if all input sections also have it set. (#125689, #134798)

- For AArch64 and ARM, added `-zexecute-only-report`, which checks for missing `SHF_AARCH64_PURECODE` and `SHF_ARM_PURECODE` section flags on executable sections. (#128883)

- For AArch64, `-z nopac-plt` has been added.

- For AArch64 and X86_64, added `--branch-to-branch`, which rewrites branches that point to another branch instruction to instead branch directly to the target of the second instruction. Enabled by default at `-O2`.

- For AArch64, added support for `-zgcs-report-dynamic`, enabling checks for GNU GCS Attribute Flags in Dynamic Objects when GCS is enabled. Inherits value from `-zgcs-report` (capped at `warning` level) unless user-defined, ensuring compatibility with GNU ld linker.

- The default Hexagon architecture version in ELF object files produced by lld is changed to v68. This change is only effective when the version is not provided in the command line by the user and cannot be inferred from inputs.

- For LoongArch, the initial-exec to local-exec TLS optimization has been implemented.

- For LoongArch, several relaxation optimizations are supported, including relaxation for `R_LARCH_PCALA_HI20/LO12` and `R_LARCH_GOT_PC_HI20/LO12` relocations, instruction relaxation for `R_LARCH_CALL36`, TLS local-exec (`LE`)/global dynamic (`GD`)/ local dynamic (`LD`) model relaxation, and TLSDESC code sequence relaxation.

- For RISCV, an oscillation bug due to call relaxation is now fixed. (#142899)

- For x86-64, the `.ltext` section is now placed before `.rodata`.

### Breaking changes

- Executable-only and readable-executable sections are now allowed to be placed in the same segment by default. Pass `--xosegment` to lld in order to get the old behavior back.

- When using `--no-pie` without a `SECTIONS` command, the linker uses the target’s default image base. If `-Ttext=` or `--section-start` specifies an output section address below this base, there will now be an error. `--image-base` can be set at a lower address to fix the error. (#140187)

### COFF Improvements

- `/thinlto-distributor` and `/thinlto-remote-compiler` options added to support Integrated Distributed ThinLTO. (#147265)

### MinGW Improvements

### MachO Improvements

### WebAssembly Improvements

#### Fixes