ld: Prevent `_tls_used` and `_load_config_used` from being garbage-collected
Prevents linker garbage collection of `_tls_used` and `_load_config_used` symbols on Windows, fixing broken executables.
This patch prevents the ld linker from garbage-collecting the _tls_used and _load_config_used symbols when the --gc-sections option is used. These symbols are crucial for the PE executable format on Windows, as their Relative Virtual Addresses (RVAs) are written into the PE header. Recent changes in mingw-w64 made these symbols only linked on demand, leading to their removal by garbage collection and resulting in broken executables. The patch adds these symbols to a list that ld will not garbage-collect, ensuring correct executable generation.
- proposer
Submits a patch to prevent garbage collection of `_tls_used` and `_load_config_used` symbols in `ld`, which is necessary for `--gc-sections` with recent mingw-w64 changes that caused broken executables.
“Earlier today I pushed some patches to mingw-w64 to make `_tls_used` only linked on demand, by referencing it indirectly through tentative definitions. However, since the startup code no longer has strong references to `_tls_used`, if LD is passed `--gc-sections`, it garbage-collects `_tls_used`, resulting in a broken executable:”
- reviewer
Acknowledges the issue and the proposed solution, asking for confirmation on whether the fix should include all PE targets or only specific ones like i386pe.
“On 27.07.2026 17:38, LIU Hao wrote: > From: LIU Hao <lh_mouse@126.com> > > Earlier today I pushed some patches to mingw-w64 to make `_tls_used` only > linked on demand, by referencing it indirectly through tentative definitions. > However, since the startup code no longer has strong references to `_tls_used`, > if LD is passed `--gc-sections`, it garbage-collects `_tls_used`, resulting in > a br…”
- contributor
Responds to Jan Beulich's query, providing the corrected patch that includes conditional compilation for `TARGET_IS_i386pe` to handle different symbol naming conventions.
“--- a/ld/emultempl/pe.em +++ b/ld/emultempl/pe.em @@ -1573,6 +1573,16 @@ gld${EMULATION_NAME}_after_open (void) pe_output_file_set_long_section_names (link_info.output_bfd); + /* The RVAs of these symbols will be written into the PE header, so they + must not be collected. */ +#if defined (TARGET_IS_i386pe) + lang_add_gc_name ("__tls_used"); + lang_add_gc_name ("__load_config_used"…”
Technical Tradeoffs
- Prevents executable corruption on Windows by retaining essential symbols.
- Slightly increases executable size by ensuring `_tls_used` and `_load_config_used` are not garbage collected.
In Details
This patch modifies the PE (Portable Executable) emulation file for ld to prevent the garbage collection of __tls_used and __load_config_used symbols. These symbols are essential for the TLS (Thread-Local Storage) and Load Configuration Directory structures in Windows executables. Recent changes in the mingw-w64 startup code led to these symbols being defined only tentatively, making them subject to --gc-sections. This change ensures they are retained, preserving the integrity of the PE header which relies on their presence and RVAs.
- ld
- The GNU linker, responsible for combining object files and libraries into an executable or shared library.
- PE
- Portable Executable, the file format for executables, object code, and DLLs used in 32-bit and 64-bit versions of Windows operating systems.
- --gc-sections
- A linker option that enables garbage collection of unused sections in the output file. This helps reduce the final executable size.
- mingw-w64
- A widely used fork of the MinGW project that provides a C compiler (GCC) and development tools for creating Windows applications, supporting both 32-bit and 64-bit targets.
- RVA
- Relative Virtual Address. An address relative to the base address of the image, used in PE executables.
- TLS
- Thread-Local Storage. A mechanism that allows threads to have their own private copy of a variable.