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

mold 2.0.0

Mold 2.0.0 is a new major release of our high-speed linker. With this release, we've transitioned our license from AGPL to MIT, aiming to expand the user base of our linker. This was not an easy decision, as those who have been following our progress know that we've been attempting to monetize our product through an AGPL/commercial license dual-licensing scheme. Unfortunately, this approach didn't meet our expectations. The license change represents our acceptance of this reality. We don't want to persist with a strategy that didn't work well.

As always, we welcome new GitHub sponsors. If you are happy with the license change, please consider becoming a sponsor.

In addition to the license change, here is a list of updates we have made in this release:

• Previously, mold could not produce an object file with more than 65520 sections using the --relocatable option. Now the bug has been fixed. (2e8bd0b)
• mold now interprets -undefined as a synonym for --undefined instead of -u ndefined. This seems inconsistent, as -ufoo is generally treated as -u foo (which is an alias for --undefined foo), but this is the behavior of the GNU linkers and LLVM lld, so we prioritize compatibility over consistency.
• -nopie is now handled as a synonym for --no-pie.
• [RISC-V] R_RISCV_SET_ULEB128 and R_RISCV_SUB_ULEB128 relocation types are now supported (4bffe26, 1ac5fe7)
• [PPC64] R_PPC64_REL32 relocation type is now supported. (ebd780e)

mold 1.11.0

mold 1.11.0 is a new release of the high-speed linker. This is not a big release but includes general improvements and bug fixes.

New features

• IBM Power10 has been supported. Previously, mold created broken executables for that target. (5065547)
• --hash-style=none has been added to cancel --hash-style=sysv, --hash-style=gnu or --hash-style=both. (ec75633)
• [ARM32] R_ARM_PLT32 relocation type has been supported. (e505900)
• [RISC-V] R_RISCV_PLT32 relocation type has been supported. (51845ac)

Bug fixes and compatibility improvements

• Previous versions of mold failed to link some programs in rare corner cases if Link-Time Optimization (LTO) is enabled. These bugs have been fixed. (e1a7590, 62d6537)
• mold used to ignore dependencies between DSOs. Since this version, if a required DSO depends on other as-needed DSO, mold keeps the latter DSO as a required one. This improves compatibility with GNU linkers. (1adde7a)
• [x86-64] mold can now link object files generated by old buggy versions of GCC. (d2970e0)
• [x86-64] Previously, a program with a very large .bss section may fail to link due to R_X86_64_REX_GOTPCRELX relocation overflow (#975). This bug has been fixed. (627bf7c)

Acknowledgements

mold is an open-source project, and we accept donations via GitHub Sponsors and OpenCollective. We thank you to everybody 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:

• Wei Wu
• Cybozu, Inc.
• Signal Slot Inc.
• Mercury
• 300baud
• G-Research-OSS
• kyle-elliott
• Jinkyu Yi
• Sanjeev
• Johan Andersson
• nasa
• Luke Kasz
• Matt Godbolt
• Brett Slatkin
• Dougall Johnson
• Santiago Pastorino
• JoJo
• daquexian
• Markus Schirp
• Javier Blazquez
• Jonathan Goodman
• Kristof Mulier
• Sebastian Dröge

mold 1.10.1

mold 1.10.1 contains only the following bug fix:

• mold 1.10.0 had a buffer overrun bug that causes the linker to terminate immediately if compiled with -D_GLIBCXX_ASSERTIONS. We fixed the unsafe memory access in this release. (7e65546)