mold 2.35.1

mold 2.35.1 is a maintenance release of the high-speed linker. It includes the following bug fixes:

• mold guarantees that outputs are reproducible, meaning that if you provide the exact same set of input files and command-line options to the same version of mold, the output is assured to be byte-for-byte identical. However, there was a bug where the --icf option caused outputs to be indeterministic, even though all possible outputs were logically correct (#1377). This issue has now been resolved. (2a78b1b)
• [RISC-V] Support for obsolete GP-relative relocations has been removed. These relocations were ratified (riscv-non-isa/riscv-elf-psabi-doc@d49e480) but then removed (riscv-non-isa/riscv-elf-psabi-doc@ad02546) from the processor-specific ABI. There are no known real-world use cases for these relocations. (04066d1)

mold 2.35.0

mold 2.35.0 is a new release of the high-speed linker. It includes the following new features and bug fixes.

New features

• Big-endian ARM64 is now supported. ARM64 is a bi-endian processor, meaning that the processor can run in either little- or big-endian mode. Even though little-endian is the de facto standard, the ARM64 processor-specific ABI defines its big-endian variant, and the ARM toolchain supports it. Now we support it too. (882e7eb)
• Big-endian SH4 is now supported. SH4 has become a minor CPU nowadays, and its big-endian variant is even more so, but some SHARP scientific calculators still use SH4 processors in big-endian mode. (0cb9fc6)

Bug fixes and compatibility improvements

• mold attempts to overwrite an existing file if a specified output file already exists because reusing an existing file is much faster than creating a fresh file and writing to it on Linux. If an existing file is currently running, open(2) for that file fails with ETXTBSY. When that happens, mold falls back to creating a new file. The problem here is that Linux kernel version 6.11 changed that well-known behavior of open(2), and it now allows user programs to overwrite a running executable. That caused a very mysterious issue for programs that rebuild themselves during the build, such as gcc or ninja (#1361). Even though the kernel's change has been reverted (torvalds/linux@3b83203), we need to make adjustments to mold for that particular version of the Linux kernel. So, if mold detects that it is running on Linux 6.11, it no longer tries to reuse an existing output file. (8e4f7b5)
• On rare occasions, mold could fail with a "ConcurrentMap is full" error. Now the issue has been resolved. (e56b649)
• Even if a user choose not to use mimalloc memory allocator (i.e. built mold with -DMOLD_USE_MIMALLOC=0), mold was still being built with mimalloc. This issue has been resolved. (ffd10dd)
• [s390x] s390x uses nonstandard 8-byte entries for the .hash section. Previously, mold created 4-byte entries for .hash, which caused mold-generated executables to crash on startup if they were built with -Wl,--hash-style=sysv. Now, mold generates a psABI-compliant .hash section. (e2e1146)

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:

• Ahrefs
• VMind AI
• Cybozu, Inc.
• Signal Slot Inc.
• Bryant Biggs
• kraptor23
• Mercury
• G-Research-OSS
• Jinkyu Yi
• David Wells
• Ville Vesilehto
• Mercedes-Benz Group
• CubeSoft, Inc.
• superfunc
• Miguel I. Solano
• Wei Wu
• daquexian
• Josh Triplett
• nomeaning
• Igor Matuszewski
• Rahul Butani
• Kyle Lacy
• Martin Liška
• Foxie Solutions

mold 2.34.1

mold 2.34.1 is a maintenance release of the high-speed linker. It includes the following bug fixes.

Bug fixes and compatibility improvements

• [ARM32] Fixed a regression that R_ARM_TARGET1 wasn't handled as a synonym for R_ARM_ABS32 relocation. This issue caused some ARM32 programs to crash on startup if linked with mold. (186272a)
• [RISC-V] mold now sets the STO_RISCV_VARIANT_CC dynamic tag if the ELF module exports a function symbol with a non-standard calling convention. (16eb513)

mold 2.34.0

mold 2.34.0 is a new release of the high-speed linker. It includes the following new features and bug fixes.

New features

• [ARM32] mold now deduplicates exception handling records in a .ARM.exidx section to reduce the size of the table. (742ea87)
• [LoongArch] TLSDESC relocations are now supported. (dbaa6d7)

Bug fixes and compatibility improvements

• --build-id=fast is now supported for compatibility with LLVM lld. mold handles it as a synonym for --build-id=sha256. (afc52ee)
• Previously, if the same symbol was provided both by a static archive and dynamic library, and if the symbol's visibility was hidden, mold sometimes failed to link it and handled the symbol as if it were undefined. Now, mold can correctly link such programs. (1efbe3f)
• Under rare circumstances, mold could create corrupted binaries if they were linked with --retain-symbols-file. This bug has been fixed. (0ee12e4)
• [LoongArch] R_LARCH_CALL36 relocation with a large offset is now correctly written. (1c32102)
• [FreeBSD] If all thread-local variables in a program have no initial values, mold-produced executables could crash or misbehave on FreeBSD. This bug has been fixed. (f6822fb)

Dropped features

• DEC Alpha support has been removed due to lack of demand. In fact, mold's Alpha support has never been tested for real-world programs and was likely unable to link them in the first place. This should not affect anyone because the last Alpha processor was released more than 20 years ago. (3711ddb)

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
• Wei Wu
• daquexian
• CubeSoft, Inc.
• Foxie Solutions
• nomeaning
• Richard Zak
• Igor Matuszewski
• Josh Triplett
• Aapo Alasuutari
• Martin Liška

mold 2.33.0

mold 2.33.0 is a new release of the high-speed linker. It includes the following new features and bug fixes.

New features

• mold gained a new linker flag --separate-debug-file to bundle debug info sections into a separate file instead of putting them into a main output file. You can optionally specify a filename in the form of --separate-debug-file=<filename>. By default, a debug info file is created in the same directory as the main output file with the .dbg extension. mold embeds the debug file's filename into the main output file so that gdb can automatically follow the link to find debug info when debugging the main output file.

  The main objective of this flag is to speed up the mold linker even more. By default, mold creates a separate debug file in the background after creating a main output file, so that you can start running the executable as soon as possible while mold is still working on linking its debug info sections. For example, linking clang with debug info normally takes ~1.70s on a Threadripper 7980X machine, while it takes only ~0.52s with --separate-debug-info. Shaving off a full second in quick edit-rebuild-run cycles should improve programmers' productivity. If you do not want mold to work in the background, pass the --no-detach option. (596ffa9)

• mold now supports the --no-allow-shlib-undefined flag. If the option is given, mold checks if all undefined symbols are resolved not only for input object files but also for shared libraries passed to the linker. To use the feature, you need to pass all shared libraries, including transitively dependent ones, to the linker so that the linker can resolve all symbols that are available at runtime. (3001f02)

• mold gained the --dynamic-list-data flag for the sake of compatibility with GNU ld. If the flag is given, all data symbols are exported as dynamic symbols. (dd8d971)

• [x86-64] -z x86-64-v2, -z x86-64-v3, -z x86-64-v4 flags are supported. (5606087)

Bug fixes and compatibility improvements

• [x86-64] Recent x86-64 processors support Intel CET to protect control flow integrity. When the feature is enabled, the instruction that is executed immediately after an indirect branch must be endbr64 or a CPU fault will raise. In other words, it restricts the locations where the control can transfer to with indirect branches. Doing that makes ROP attacks harder to conduct.

  A problem with that is the compiler needs to conservatively emit an endbr64 at the beginning of each global function because the compiler doesn't know whether or not the function's address is taken in other translation units. As a result, the resulting binary contains more endbr64s than necessary, weakening the protection.

  mold supports the -z rewrite-endbr option to conduct a whole program analysis and rewrite endbr64 with nop if a function's address is not actually taken within the program. Previously, mold didn't take section symbols into account when conducting the analysis, which resulted in culling some endbr64s that must not be removed. Now, the bug has been fixed. We confirmed that mold can build itself with -z rewrite-endbr, and the resulting mold executable works fine with Intel CET. (ed7eec5)

• mold now creates a .eh_frame section even if it's empty. (14a4b05)

• [LoongArch] The following relocations are now supported: R_LARCH_TLS_LE_HI20_R, R_LARCH_TLS_LE_ADD_R, R_LARCH_TLS_LE_LO12_R, R_LARCH_CALL36, R_LARCH_RELAX (36e5b4b, 98a7cff, 2c6f379)

• [LoongArch] Some relaxations that reduce the section size are now supported. (74b359f, 121f917)

• [LoongArch] Range extension thunk support has been removed in favor of R_LARCH_CALL36 relocations. (47c092a)

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:

• Bloomberg
• Cybozu, Inc.
• Ahrefs
• Signal Slot Inc.
• Mercury
• G-Research-OSS
• Jinkyu Yi
• kraptor23
• Richard Zak
• Wei Wu
• daquexian
• CubeSoft, Inc.
• Josh Triplett
• Foxie Solutions
• nomeaning
• Igor Matuszewski
• Dougall Johnson

mold 2.32.1

mold 2.32.1 is a maintenance release of the high-speed linker.

Bug fixes and compatibility improvements

• Previously, shared libraries specified with --as-needed were not considered as "needed" if they were referenced only by weak undefined symbols. Such weak symbols were converted to absolute symbols at address zero at link-time. Although this behavior was not technically wrong, it caused a significant issue in a rare occasion (#1286). Now, weak undefined symbols retain --as-needed shared libraries. (06b5926)
• [RISC-V] RISC-V object files contain ISA strings in the .riscv.attributes section. Previously, we had reported valid ISA strings containing digits as errors. The issue has now been resolved. (841a186)
• [RISC-V] We no longer write dynamic relocation addends to relocated places because it caused static position-independent executables to crash on process startup in some environments. In other words, --no-apply-dynamic-relocs is enabled by default.
• LTO now works on MinGW. (50bf031)

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.
• Ahrefs
• Signal Slot Inc.
• Mercury
• G-Research-OSS
• Jinkyu Yi
• kraptor23
• Wei Wu
• daquexian
• Dougall Johnson
• CubeSoft, Inc.
• Foxie Solutions
• nomeaning
• Igor Matuszewski
• Josh Triplett

mold 2.32.0

mold 2.32.0 is a new release of the high-speed linker. It includes the following new features and bug fixes:

New features

• mold supports a feature called Identical Code Folding, or ICF. As the name suggests, ICF finds identical functions and merges them to reduce the size of an output file. This is especially effective for template-heavy C++ programs since templates tend to be instantiated to the same machine code for different types. For example, std::vector<int> is likely to be instantiated to the same code as std::vector<unsigned>. We've made an improvement to our ICF algorithm so that the --icf feature is ~50% faster than the previous version. (fa8e95a)
• The -z rodynamic option is now supported for compatibility with LLVM lld. With the option, mold places the .dynamic section into a read-only segment. (9a233df)

Bug fixes and compatibility improvements

• Previously, mold behaved differently compared to other linkers if both -z defs and --undefined=ignore-in-object-files were given (#1270). Now, they override each other so that the mold's behavior is compatible with others. (8cd85aa)
• Previously, --dependency-file mistakenly recorded response files as dependencies (#1258). This bug has been fixed. (4281f45)
• There was a bug that mold corrupted debug info section contents when the --relocatable option was given (#1265). This issue has been fixed. (08b0a16)
• [PPC64] The R_PPC64_TPREL16_LO_DS relocation type is supported. (a8cd2e8)
• [ARM64, PPC64, LoongArch] mold 2.31.0 or earlier may have failed with an assertion failure when creating a large output file (#1224). This issue has been resolved. (c7c8583)

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.
• kraptor23
• Mercury
• G-Research-OSS
• Jinkyu Yi
• CubeSoft, Inc.
• Wei Wu
• daquexian
• Dougall Johnson
• Josh Triplett
• Foxie Solutions
• nomeaning
• Igor Matuszewski

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