riscv: Ignore attributes in empty input file
This patch fixes multiple RISC-V linker test failures by ignoring attributes in empty input files during attribute merging.
This patch addresses multiple failures in the RISC-V linker tests by ignoring attributes found in empty input files when merging attributes. This change specifically impacts scenarios involving garbage collection of sections (--gc-sections), defined symbols (--defsym), KEEP directives, and LTO (Link-Time Optimization). Ignoring attributes in empty files resolves issues related to incorrect magic number detection and improves the linker’s ability to handle various scenarios, ultimately fixing PR ld/34185.
- proposer
Proposes ignoring empty and `.note.gnu.build-id` sections when merging attributes to fix multiple RISC-V linker test failures.
“Ignore empty and .note.gnu.build-id sections when merging attributes. The following linker tests now pass for riscv: FAIL: Diagnostics - Wrong magic number mixed with valid CTF sections FAIL: --gc-sections with --defsym FAIL: --gc-sections with KEEP ...”
- proposer
The patch fixes multiple RISC-V linker test failures.
“Ignore empty and .note.gnu.build-id sections when merging attributes. The following linker tests now pass for riscv:”
Technical Tradeoffs
- Ignoring attributes in empty files might hide genuine errors, but the patch assumes that attributes in empty files are generally not meaningful.
In Details
The patch modifies _bfd_riscv_elf_merge_private_bfd_data in elfnn-riscv.c to ignore attributes in empty input files during the attribute merging process. This resolves issues where the linker incorrectly detected magic numbers or mishandled section garbage collection due to the presence of attributes in empty or .note.gnu.build-id sections. The fix is necessary for correct LTO and symbol handling.
For Context
When linking object files to create an executable, the linker combines information from all input files, including attributes that describe various properties of the code and data. This patch addresses a problem in the RISC-V linker where it was incorrectly processing attributes found in empty input files. By ignoring these attributes, the linker can now correctly handle scenarios such as garbage collection of unused code sections and link-time optimization, leading to more reliable and efficient executables.