AArch64 GAS: Reject nonzero GOT-entry relocation addends
Patch enforces zero addends for specific AArch64 GOT-entry relocations as required by AAELF.
Sivan Shani submits a patch to the AArch64 assembler (GAS) that enforces the AAELF requirement for zero addends on relocations involving GDAT, GTLSIDX, GTPREL, or GTLSDESC operations. The patch introduces a common predicate to identify these relocation types and rejects non-zero addends, ensuring symbol identity preservation. New tests for both LP64 and ILP32 ABIs are included.
- proposer
Submitted a patch to enforce zero addends for specific AArch64 GOT-entry relocations, adding tests for LP64 and ILP32.
“AAELF requires relocations using GDAT, GTLSIDX, GTPREL or GTLSDESC operations to have a zero addend. Add a common predicate for the affected BFD relocation codes. Use it in tc_gen_reloc to reject nonzero addends before PC-relative adjustment, and in aarch64_fix_adjustable to preserve symbol identity. Add LP64 and ILP32 tests covering rejected +1/-1 expressions and accepted +0/-0 expressions fo…”
In Details
This patch addresses a compliance issue in the AArch64 backend of GAS concerning Global Offset Table (GOT) entries. Specifically, it enforces the AAELF standard's requirement that certain GOT-related relocations (GDAT, GTLSIDX, GTPREL, GTLSDESC) must have a zero addend. The change involves adding a new predicate function aarch64_reloc_creates_got_entry_p to identify these relocations and integrating checks in tc_gen_reloc and aarch64_fix_adjustable to reject non-zero addends. New test cases are provided for both LP64 and ILP32 data models.
- AArch64
- The 64-bit ARM architecture.
- GAS
- The GNU Assembler, part of the GNU Binutils project.
- GOT
- Global Offset Table. A data structure used in position-independent code (PIC) to store addresses of external functions or global variables.
- Relocation
- A process performed by the linker to adjust symbolic addresses in machine code after it has been assembled, ensuring correct addresses at runtime.
- Addend
- A constant value added to a symbol's address during the relocation process.
- AAELF
- Arm Architecture ELF (Executable and Linkable Format) specification. Defines the object file format and conventions for the Arm architecture.
- LP64
- A data model where long pointers and integers are 64-bit. Used in many 64-bit operating systems, including AArch64.
- ILP32
- A data model where integers are 32-bit, but pointers are also 32-bit. It's a variant for 64-bit architectures like AArch64.