mold 2.31.0

mold 2.31.0 is a new release of the high-speed linker. It includes the following new features and bug fixes:

New features

• mold is now up to 10% faster when linking very large, debug info-enabled executables such as Blender (~1.8 GiB) or Clang (~3.8 GiB), thanks to several improvements we've made to the string merging algorithm. (53ebcd8, d714301, 40f6b17, c9faf3d)
• -z start-stop-visibility=hidden is now supported so that linker-synthesized __start_<section-name> and __stop_<section-name> symbols can be completely hidden from other ELF modules. Previously, only -z start-stop-visibility=protected was supported. (99a5b15)
• -Bsymbolic-non-weak and -Bsymbolic-non-weak-functions options are now supported for compatibility with LLVM lld. Just like lld, these options control which symbols are exported as dynamic symbols. -Bsymbolic-non-weak makes the linker to export only weak symbols, whereas -Bsymbolic-non-weak-functions makes it to export only weak function symbols. (7d17aa8)

Bug fixes and compatibility improvements

• Previously, if a linker script contains a newline character in the beginning four bytes of a file, it was not recognized as a linker script by mold. Now, mold allows newlines at the beginning of a file. (ea054cc)
• Under rare circumstances, the INPUT linker script command may have found a different file than GNU ld would. Now, mold's behavior aligns with GNU ld's. (163975d)
• Previously, the --repro option produced corrupted tar files. Now the bug has been fixed. (32c4a09)
• mold generally guarantees that its output is reproducible, meaning that if you run the linker with the exact same command line options and input files, the output is guaranteed to be bit-for-bit identical to the previous outputs. However, under rare circumstances, it might produce different output due to a bug. It's reported that this nondeterminism caused random crashes for some programs (#1247). This bug has been fixed. (6463a7c)
• mold no longer sets the address of the .text section as the entry point address if --entry option is not given, just like LLVM lld. (020b1a7)
• [RISC-V] __global_pointer$ symbol is now exported from executables as required by the processor-specific ABI. (3df7c8e)
• [ARM32] --long-plt option is now recognized as known option by mold. mold ignores the option, though, because the PLTs generated by our linker is always long. (d432e98)

Acknowledgements

mold is an open-source project, and we accept donations via GitHub Sponsors and OpenCollective. We thank everyone who sponsors our project. In particular, we'd like to acknowledge the following organizations and people who have sponsored $32/mo or more during this release cycle:

• Cybozu, Inc.
• Signal Slot Inc.
• Mercury
• G-Research-OSS
• Jinkyu Yi
• kraptor23
• a_p_u_r_o
• Rodrigo Salazar
• Wei Wu
• daquexian
• Matt Godbolt
• Dougall Johnson
• CubeSoft, Inc.
• Josh Triplett
• Robey Pointer
• nomeaning
• David Wells
• Foxie Solutions
• Yihao Ke
• darkdragon-001
• Nazar Mokrynskyi
• Martin Liška
• Richard Zak
• Igor Matuszewski
• Santiago Pastorino
• Hunter Kvalevog

mold 2.30.0

mold 2.30.0 is a maintenance release of the high-speed linker. It includes the following minor bug fixes:

• We have increased the version number from 2.4.1 to 2.30.0, even though this release contains only minor bug fixes. This change was made to prevent GNU libtool from mistaking mold 2.4.1 for GNU ld 2.4.1, which led it to incorrectly conclude that our linker was an outdated version of the GNU linker. Bumping up the version number to align with GNU ld may not be the most elegant solution, but it is a practical approach to resolve the compatibility issue with GNU libtool. (c7f6a91)
• Previously, mold may have inserted an unnecessary gap before the .bss section in an output file, thereby creating an extra segment for it. While not technically incorrect, it was certainly unnecessary. mold 2.30.0 eliminates this unnecessary on-disk gap for .bss. (c395da1)
• Previously, under rare circumstances, mold might fail with the "ConcurrentMap is full" error message if --gdb-index was used. This bug has been resolved. (c60d1d0)
• Previously, mold might generate an excessive number of "ignoring .llvm_addrsig section without sh_link" warnings. These warnings are now suppressed. (51f871f)
• Sections with unknown section types are now reported as errors. (d21207c)
• [PPC32] A crash bug related to --gc-sections has been fixed. (8eae0a3)

Acknowledgements

mold is an open-source project, and we accept donations via GitHub Sponsors and OpenCollective. We thank everyone who sponsors our project. In particular, we'd like to acknowledge the following organizations and people who have sponsored $32/mo or more during this release cycle:

• Signal Slot Inc.
• Mercury
• G-Research-OSS
• kraptor23
• Cybozu, Inc.
• Jinkyu Yi
• Matt Godbolt
• Robey Pointer
• David Wells
• Brett Slatkin
• Dougall Johnson
• CubeSoft, Inc.
• Rodrigo Salazar
• Yihao Ke
• Richard Zak
• Wei Wu
• daquexian
• Santiago Pastorino
• Josh Triplett
• nomeaning

mold 2.4.1

mold 2.4.1 is a maintenance release of the high-speed linker. It contains the following minor bug fixes.

• mold 2.4.0 or prior may promote weak dynamic symbols to strong ones under a rare circumstance, which caused "undefined symbol" error at runtime. The bug has been fixed. (50bdf39)
• Previously, if two or more VERSION clauses in a version script match to the same symbol, the first one took precedence. This was incompatible with GNU ld, which gives the last one the highest priority, causing a Qt library link failure. This compatibility issue has been resolved. (e1e16bf)
• By default, we demangle symbols in error messages so that they are easier to read. Previously, Rust symbols could accidentally be demangled as C++ symbols. Now, mold attempts to demangle symbols as Rust ones only for object files created by rustc. (ea9864b)
• [RISC-V] mold now relaxes a GOT-load instruction sequence into a direct address materialization if the symbol address is known at link time. This relaxation eliminates one memory load and slightly improves the linked program's performance. (2ccaa81)
• [PowerPC64 ELFv2] GCC may emit references to _savegpr0_*, _restgpr0_*, _savegpr1_* and _restgpr1_* symbols for the -Os command line option to optimize the output for code size. These symbols are not defined by any object file and expected to be synthesized by the linker. mold didn't use to synthesize these symbols, and therefore object files created with -Os sometimes failed due to missing symbol errors. Now, mold synthesizes these symbols. (d4ff48a)
• [PowerPC64] R_PPC64_DTPREL16_LO_DS relocation type has now been supported. (6d8e6af)
• [Illumos] On Illumos OS, absolute symbols in DSOs need to be resolved at runtime because the dynamic linker treats such symbols in a special manner. Previously, mold directly used absolute symbol addresses at link-time and did not place them into the dynamic symbol table. That optimization has been removed for compatibility with Illumos. (bed5b17, 7f8d77d)

Acknowledgements

mold is an open-source project, and we accept donations via GitHub Sponsors and OpenCollective. We thank everyone who sponsors our project. In particular, we'd like to acknowledge the following organizations and people who have sponsored $32/mo or more during this release cycle:

• Cybozu, Inc.
• Wei Wu
• Signal Slot Inc.
• Mercury
• G-Research-OSS
• Jinkyu Yi
• kraptor23
• kyle-elliott
• Emerge Tools
• nomeaning
• daquexian
• Matt Godbolt
• Brett Slatkin
• Dougall Johnson
• Santiago Pastorino
• CubeSoft, Inc.
• Josh Triplett
• David Wells
• Martin Liška
• Richard Zak

mold 2.4.0

mold 2.4.0 is a new release of the high-speed linker.

New features

• mold gained the --spare-program-headers=<number> option, which adds a specified number of spare entries at the end of the program header. The option aims to make post-processing tools to add program header entries very easily. Note that sorting program header entries after adding new ones may be necessary to meet the constraints of the ELF file format. For details, see the elf(5) man page. (eb6c213)
• mold's -z rewrite-endbr option rewrites superflous endbr64 instructions with nop as a countermeasure against control-flow highjacking attacks. Previously, this worked exclusively with object files compiled with -ffunction-sections, requiring each function to be compiled into a separate section. Starting from this release, -z rewrite-endbr works on object files compiled without it. In other words, mold is now capable of rewriting endbr64 instructions even if the instruction is not at the beginning of a section. (3cb8a52)

Bug fixes and compatibility improvements

• Previously, mold couldn't handle object files containing multiple .eh_frame sections. The .eh_frame is a section containing data for exception handling. Usually, an object file contains only one .eh_frame which describes how to handle exceptions for all text sections in the same file. However, on rare conditions, it seems ld -r creates an object file containing multiple .eh_frame sections. mold is now able to handle such object files. (f4c5a8a)
• mold -run <command> is an easy way to run the given command with a virtual environment in which the ld command is replaced with mold. The feature is implemented using LD_PRELOAD to hook fork(2)-family functions. Before this release, some invocations of ld were not intercepted correctly because we missed the posix_spawnp(2) function. Now, the function is intercepted just like other fork(2)-family functions. (3fd1cec)
• mold used to produce a non-working executable on a rare occasion when all thread-local variables lacked an initial value and the read-only data required alignment equal to or greater than the page size. This bug has been resolved. (de7d37e)
• Previously, mold might assign a different symbol version to a symbol compared to GNU ld if it matches both a wildcard pattern and an exact pattern in a version script. Our behavior is now compatible with that of GNU ld. (0fdbace)
• [x86-64, i686] Recent versions of LLVM emit a machine code sequence for TLSDESC thread-local variables that differs from GCC's, and mold previously mis-optimized this sequence, leading to crashes in the linked programs. In other words, if you are using LLVM/Clang and compile object files with -mtls-dialect=gnu2, mold might mis-optimize the output file. Now, the bug has been fixed. (000ce0e)

Acknowledgements

mold is an open-source project, and we accept donations via GitHub Sponsors and OpenCollective. We thank everyone who sponsors our project. In particular, we'd like to acknowledge the following organizations and people who have sponsored $32/mo or more during this release cycle:

• Cybozu, Inc.
• Bryant Biggs
• Signal Slot Inc.
• Mercury
• G-Research-OSS
• Jinkyu Yi
• Emerge Tools
• kyle-elliott
• kraptor23
• David Wells
• Kiril Mihaylov
• daquexian
• Brett Slatkin
• Dougall Johnson
• Santiago Pastorino
• CubeSoft, Inc.
• Josh Triplett
• Rahul Butani
• Kyle Lacy

mold 2.3.3

mold 2.3.3 contains the following bug fixes:

• --dynamic-list has different semantics for executables and DSOs. Previously, mold implemented only the semantics for executables, causing issues with libraries such as musl that used this option. mold now handles the option for DSOs correctly. (da3f5dd)
• Old object files often contain .ctors and .dtors sections, which hold function pointers for initializing and finalizing processes, respectively. Their roles have been superseded by .init_array and .fini_array on most targets. mold worked functioned correctly as long as input object files consistently use the old or the new sections. However, mixing object files that contain both types of initializers/finalizers resulted in some functions not being executed. This issue has been fixed. (3f88964)
• --defsym can cause the linker to crash if a given symbol is not defined. The crash bug has been fixed. (ff3d54d)
• [POWER10] On rare occasions, pointers statically initialized to functions could be left as null pointers. This bug has been fixed. (31c3b53)

Additionally, our dist.sh script that we use to create binary packages attached to the release notes pages is now reproducible. That means the script always creates bit-for-bit identical output for the same git commit, irrespective of the OS versions or environments in which it's run. This property is very useful as a countermeasure against supply chain attacks. You can now verify that the binaries we distribute are indeed built from the released version of source files by rebuilding the binaries yourself and comparing the outputs.

mold 2.3.2

mold 2.3.2 contains the following bug fixes.

• mold no longer emits dynamic relocations against the text segment for GNU ifunc symbols. Previously, mold emitted such relocations for position-dependent executables. (4cdfc7e)
• mold no longer reports the "REL-type relocation table is not supported for this target" error and instead ignore incompatible relocation tables. LLVM generates such non-conforming relocation tables for the .llvm.call-graph-profile section. This change was made for compatibility. (3791900)
• mold now pads unused gaps in the text segment with interrupt or NOP instructions, instead of leaving them filled with zeros. This alteration does not change the program's semantics but prevents disassemblers from interpreting the spaces between functions as valid instructions. (c86a59a)
• mold now creates the .mold-lock file for MOLD_JOBS not in the home directory but in $XDG_RUNTIME_DIR, which is usually /var/user/<uid>. (39cdf61)
• [ARM32] There was an issue preventing mold from being built on an ARMv8 64-bit ARM processor with an ARM32 userland, such as the 32-bit Raspberry Pi OS running on a Raspberry Pi 4. This build issue has been resolved. (02ead29)
• [LoongArch] mold can now handle R_LARCH_PCALA_LO12 relocation for the jirl instruction. (d3188e3)

mold 2.3.1

mold 2.3.1 contains the following bug fixes.

• [ARM32, ARM64, PowerPC, LoongArch] mold 2.3.0 would crash when handling large output files. This was due to a bug in the code that creates range extension thunks. This issue has now been resolved. (7be1b66)
• [LoongArch] mold is now capable of handling relocations generated for the -mcmodel=extreme flag. (4bd80ec)

mold 2.3.0

mold 2.3.0 is a new release of the high-speed linker.

New features

• [x86-64] mold 2.3.0 has introduced an experimental flag, -z rewrite-endbr, which rewrites superfluous endbr64 instructions as nop.

  endbr64 is a relatively recent x86 instruction used to mark locations where an indirect jump instruction can transfer control. With control-flow integrity enabled (meaning endbr64 is effective), an indirect jump can only target an endbr64 or it will trigger a runtime exception. This mechanism significantly hinders certain control hijacking attacks, such as ROP or JOP, since attackers cannot jump to just any location.

  When given the -fcf-protection flag, GCC conservatively places an endbr64 at the beginning of every global function. This is because the function's address might be taken as a pointer by other translation units. However, in most cases, function addresses are not actually taken. This conservative approach results in an overabundance of unnecessary endbr64 instructions, leading to not only code bloating but also a potential decrease in security as there are more locations for an attacker to exploit.

  The new linker option, -z rewrite-endbr, aims to alleviate this issue. The linker can carry out a whole-program analysis on the input files to identify functions whose addresses are never taken. If -z rewrite-endbr is specified, mold will conduct this analysis and replace the initial endbr64 with a nop for functions whose addresses aren't taken.

  mold also emits an endbr64 in a PLT entry only when the address of the PLT entry is taken. (17f0d85)

Bug fixes and compatibility improvements

• mold now produces a more compact .gdb_index section when using the --gdb-index flag. Additionally, mold now generates a correct .gdb_index section for object files created by Clang. (a396fa4)
• mold is now capable of handling input sections larger than 4 GiB. (0ce32d3)
• [PPC] mold can now generate executables for POWER10 processors. Previously, executables produced by mold would crash immediately on startup on POWER10. (0f71471)
• [ARM64] When a function with a non-standard calling convention is exported, it's mandatory for the linker to turn on the STO_AARCH64_VARIANT_PCS flag to notify the dynamic linker. mold now appropriately sets this flag. (2e3b56e)
• [RISC-V] mold now supports new GP-relative relocations. (ac3ee91)

Acknowledgements

mold is an open-source project, and we accept donations via GitHub Sponsors and OpenCollective. We thank everyone who sponsors our project. In particular, we'd like to acknowledge the following organizations and people who have sponsored $32/mo or more during this release cycle:

Signal Slot Inc.
Mercury
G-Research-OSS
Jinkyu Yi
Emerge Tools
Cybozu, Inc.
jfmontanaro
Steven Noonan
Brett Slatkin
Dougall Johnson
Santiago Pastorino
CubeSoft, Inc.
Rahul Butani
Kyle Lacy
daquexian
Josh Triplett
Kiril Mihaylov

mold 2.2.0

mold 2.2.0 is a new release of the high-speed linker.

New features

• We now use BLAKE3 as a cryptographic hash function instead of SHA256. This change has made --build-id a few percent faster. libssl is no longer a build dependency. (7f7a744)
• mold is now a few percent faster than the previous version due to an optimization of string merging code path. (1a13c50)
• mold now emits slightly optimized code for thread-local variable accesses. (f057fda, d56f528)
• [RISC-V] mold now supports TLSDESC relocations. TLSDESC is a new mechanism for faster thread-local variable access. We (@ishitatsuyuki) actually led the effort to ratify the specification (riscv-non-isa/riscv-elf-psabi-doc#373) and implement it to compiler toolchain including GCC, GNU binutils and, of course, mold. (141556d)

Bug fixes and compatibility improvements

• mold no longer marks an as-needed .so as "needed" if the .so file is not directly used by the output file. Previously, mold marked a .so file as "needed" if the .so file was used by another "needed" .so file. (f02db0f)
• [PPC64] --execute-only now works on 64-bit PowerPC. (ac20d87, 51fec5f)

Acknowledgements

mold is an open-source project, and we accept donations via GitHub Sponsors and OpenCollective. We thank everyone who sponsors our project. In particular, we'd like to acknowledge the following organizations and people who have sponsored $32/mo or more during this release cycle:

• GlareDB
• Cybozu, Inc.
• Sanjeev
• Signal Slot Inc.
• Mercury
• Jinkyu Yi
• Emerge Tools
• G-Research-OSS
• jfmontanaro
• daquexian
• Brett Slatkin
• Dougall Johnson
• Santiago Pastorino
• CubeSoft, Inc.
• Josh Triplett
• Kiril Mihaylov

mold 2.1.0

mold 2.1.0 is a new release of the high-speed linker.

New features

• Loongson's LoongArch CPU has been supported. (03b1a1c)
• -z nosectionheader has been added to eliminate section headers from the output file. (084ca55)

Bug fixes and compatibility improvements

• Previously, linking with the -z pack-relative-relocs option produces an executable that glibc 2.38 refuses to run with DT_RELR without GLIBC_ABI_DT_RELR dependency error. Now, mold produces binaries compatible with glibc 2.38. (f467ad1)
• [ARM64] R_AARCH64_ADR_PREL_PG_HI21_NC relocation type has been supported. (17a5c3e)
• [ARM64] R_AARCH64_MOVW_UABS_G3 relocation type has now been handled as a PLT-generating relocation to fix an issue when main is not defined in the main executable but rather in a .so file. (e764557)
• [RISC-V] We now merge input .riscv.attributes contents. Previously, we just concatenated them. (aa64491)

Acknowledgements

mold is an open-source project, and we accept donations via GitHub Sponsors and OpenCollective. We thank everyone who sponsors our project. In particular, we'd like to acknowledge the following organizations and people who have sponsored $32/mo or more during this release cycle:

• GlareDB
• Cybozu, Inc.
• Signal Slot Inc.
• Mercury
• Jinkyu Yi
• G-Research-OSS
• Sanjeev
• a_p_u_r_o
• Emerge Tools
• Brett Slatkin
• Dougall Johnson
• Santiago Pastorino
• daquexian
• CubeSoft, Inc.
• Bryant Biggs
• Luke Kasz
• Marko Mikulicic
• Iain H
• nasa
• Robey Pointer
• Junho Choi
• Markus Schirp
• Sebastian Dröge
• Martin Liška
• Masahiro Aoki
• Brian Gesiak
• Jonatan Klemets
• Ernesto Cambuston
• vadorovsky
• Takaki Ueno
• Yusuke Ito
• Adam Gutglick
• Florian Plattner
• Christoph Gross
• yossyX
• Dario Nieuwenhuis
• Guillaume Racicot
• Josh Triplett
• Tetsuo Kiso
• Shane Sveller
• Michael McLoughlin
• DragonflyDB
• Michael Sproul
• Brian Gianforcaro
• Kentaro Tanaka
• Shinichiro Hamaji
• strager
• JoJo
• Zhihao Yuan
• Yutaro Ohno
• Jonathan Goodman
• Wataru Sekiguchi
• José M Rico
• Vladimir Miloserdov
• kazu-42
• Foxie Solutions