gas: add --reloc-section-sym={all,internal,none} option for ELF
Adds a new option to control how GAS converts local symbols referenced by relocations to section symbols, aiding debugging and tool compatibility.
This patch introduces the —reloc-section-sym option to GAS, allowing users to control the conversion of local symbols used in ELF relocations. By default, eligible local symbols are converted to reference section symbols (STT_SECTION), which can reduce .symtab entries. The new option allows this conversion to be limited to compiler-generated locals (‘internal’) or disabled entirely (‘none’), providing greater flexibility for debugging and compatibility with tools that benefit from preserved symbol names.
- proposer
Proposes adding a new option to control the conversion of local symbols in ELF relocations to section symbols, enhancing debugging and tool integration.
“When generating relocations for non-ifunc local symbols that satisfies several conditions, GAS converts them to reference the section symbol (STT_SECTION) instead, folding the original symbol's offset into the addend. This allows the original local symbol to be omitted from .symtab, but the STT_SECTION symbol itself must be present, so the conversion saves .symtab entries only when a section has…”
- reviewer
Asks for clarification on the change to `complain_overflow_dont` and expresses confidence in the correctness of the patch.
“Which you now change to complain_overflow_dont? Not saying the change is incorrect (it certainly looks right, thanks), because if it was, I have confidence that the test-suite would trigger a failure, but that wording is confusing.”
Technical Tradeoffs
- Increases flexibility for debugging and tool integration at the cost of slightly larger symbol tables when 'none' or 'internal' options are used.
- Adds complexity to the GAS command-line interface.
In Details
This patch introduces a command-line option to GAS for fine-grained control over how local symbols involved in ELF relocations are handled. By default, GAS optimizes symbol table size by converting local symbols referenced by relocations into section symbols (STT_SECTION), effectively omitting the original local symbol. This change allows users to opt-out of this conversion ('none') or restrict it to compiler-internal symbols ('.L' prefixed, 'internal'), which is beneficial for debugging and tools that rely on explicit symbol presence.
- GAS
- The GNU Assembler, the default assembler used by the GNU Compiler Collection (GCC).
- ELF
- Executable and Linkable Format, a standard file format for executables, object code, shared libraries, and core dumps on many Unix-like systems.
- relocation
- A directive that describes how to modify code or data when an object file is linked. Relocations typically specify an address and the type of modification needed, such as patching in an offset or a symbol address.
- local symbol
- A symbol that is local to a compilation unit and not intended to be visible or used by other modules. In GAS, these often start with a '.' or '.L'.
- STT_SECTION
- A symbol type in the ELF format that represents a section itself, often used as a placeholder or for specific section-related operations.
- .symtab
- The symbol table section in an ELF file, which contains information about all symbols (functions, variables, etc.) defined or referenced in the object file.