From ab40c027f0ce9492919a72ad339de40bdb84b354 Mon Sep 17 00:00:00 2001 From: Dimitry Andric Date: Mon, 3 May 2021 20:08:49 +0200 Subject: [PATCH] [MC][ELF] Work around R_MIPS_LO16 relocation handling problem This fixes PR49821, and avoids "ld.lld: error: test.o:(.rodata.str1.1): offset is outside the section" errors when linking MIPS objects with negative R_MIPS_LO16 implicit addends. ld.lld handles R_MIPS_HI16/R_MIPS_LO16 separately, not as a whole, so it doesn't know that an R_MIPS_HI16 with implicit addend 1 and an R_MIPS_LO16 with implicit addend -32768 represents 32768, which is in range of a MergeInputSection. We could introduce a new RelExpr member (like R_RISCV_PC_INDIRECT for R_RISCV_PCREL_HI20 / R_RISCV_PCREL_LO12) but the complexity is unnecessary given that GNU as keeps the original symbol for this case as well. Reviewed By: atanasyan, MaskRay Differential Revision: https://reviews.llvm.org/D101773 --- llvm/lib/MC/ELFObjectWriter.cpp | 11 +++++++++++ llvm/test/MC/Mips/mips_lo16.s | 22 ++++++++++++++++++++++ 2 files changed, 33 insertions(+) create mode 100644 llvm/test/MC/Mips/mips_lo16.s Index: llvm-toolchain-12_12.0.1~+rc2/llvm/lib/MC/ELFObjectWriter.cpp =================================================================== --- llvm-toolchain-12_12.0.1~+rc2.orig/llvm/lib/MC/ELFObjectWriter.cpp +++ llvm-toolchain-12_12.0.1~+rc2/llvm/lib/MC/ELFObjectWriter.cpp @@ -1408,6 +1408,17 @@ bool ELFObjectWriter::shouldRelocateWith if (TargetObjectWriter->getEMachine() == ELF::EM_MIPS && !hasRelocationAddend()) return true; + + // ld.lld handles R_MIPS_HI16/R_MIPS_LO16 separately, not as a whole, so + // it doesn't know that an R_MIPS_HI16 with implicit addend 1 and an + // R_MIPS_LO16 with implicit addend -32768 represents 32768, which is in + // range of a MergeInputSection. We could introduce a new RelExpr member + // (like R_RISCV_PC_INDIRECT for R_RISCV_PCREL_HI20 / R_RISCV_PCREL_LO12) + // but the complexity is unnecessary given that GNU as keeps the original + // symbol for this case as well. + if (TargetObjectWriter->getEMachine() == ELF::EM_MIPS && + !hasRelocationAddend()) + return true; } // Most TLS relocations use a got, so they need the symbol. Even those that