[ELF][MIPS] Handle section symbol points to the .MIPS.options / .reginfo section

[atanasyan]

Summary

MIPS .reginfo and .MIPS.options sections are consumed by the linker, and the linker produces a single output section. But it is possible that input files contain section symbol points to the corresponding input section. In case of generation a relocatable output we need to write such symbols to the output file.

Fixes bug 27878.

[ruiu]

ELF/InputSection.cpp

73–74

Please use fatal instead of assert because this can be triggered by a broken user input. (use assert only for programmer's (i.e. our) errors.)

test/ELF/mips-options-r.test

13

Can't you create it using llvm-as?

[atanasyan]

• Use fatal instead of assert
• It is impossible to generate input file for the test case using llvm-mc because llvm-mc does not create section variable points to the .MIPS.options section.

[ruiu]

LGTM

ELF/InputSection.cpp

case Regular:
     return cast<InputSection<ELFT>>(this)->OutSecOff + Offset;
   case EHFrame:
     return cast<EhInputSection<ELFT>>(this)->getOffset(Offset);
   case Merge:
     return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset);
   case MipsReginfo:
   case MipsOptions:
     // MIPS .reginfo and .MIPS.options sections are consumed by the linker,
-    // so they should never be copied to output.
-    llvm_unreachable("MIPS reginfo/options section reached writeTo().");
+    // and the linker produces a single output section. It is possible that
+    // input files contain section symbol points to the corresponding input
+    // section. Redirect it to the produced output section.
+    if (Offset != 0)
+      fatal("Unsupported reference to the middle of '" + getSectionName() +
+            "' section");
+    return this->OutSec->getVA();
   }
   llvm_unreachable("invalid section kind");
 }
 
 template <class ELFT>
 typename ELFT::uint
 InputSectionBase<ELFT>::getOffset(const DefinedRegular<ELFT> &Sym) {
   return getOffset(Sym.Value);

ELF/OutputSections.cpp

void MipsReginfoOutputSection<ELFT>::writeTo(uint8_t *Buf) {
   R->ri_gprmask = GprMask;
 }
 
 template <class ELFT>
 void MipsReginfoOutputSection<ELFT>::addSection(InputSectionBase<ELFT> *C) {
   // Copy input object file's .reginfo gprmask to output.
   auto *S = cast<MipsReginfoInputSection<ELFT>>(C);
   GprMask |= S->Reginfo->ri_gprmask;
+  S->OutSec = this;
 }
 
 template <class ELFT>
 MipsOptionsOutputSection<ELFT>::MipsOptionsOutputSection()
     : OutputSectionBase<ELFT>(".MIPS.options", SHT_MIPS_OPTIONS,
                               SHF_ALLOC | SHF_MIPS_NOSTRIP) {
   this->Header.sh_addralign = 8;
   this->Header.sh_entsize = 1;
void MipsOptionsOutputSection<ELFT>::writeTo(uint8_t *Buf) {
   Reg->ri_gprmask = GprMask;
 }
 
 template <class ELFT>
 void MipsOptionsOutputSection<ELFT>::addSection(InputSectionBase<ELFT> *C) {
   auto *S = cast<MipsOptionsInputSection<ELFT>>(C);
   if (S->Reginfo)
     GprMask |= S->Reginfo->ri_gprmask;
+  S->OutSec = this;
 }
 
 namespace lld {
 namespace elf {
 template class OutputSectionBase<ELF32LE>;
 template class OutputSectionBase<ELF32BE>;
 template class OutputSectionBase<ELF64LE>;
 template class OutputSectionBase<ELF64BE>;

test/ELF/mips-options-r.test

+# Check that if input file contains .MIPS.options section and symbol
+# points to the section and the linker generates a relocatable output,
+# LLD does not crash and write section symbols point to the output
+# .MIPS.options section.
+#
+# PR 27878
+#
+# Input object file created using the following script:
+# % cat t.s
+#   .text
+#   nop
+# % as -mabi=64 -mips64r2 t.s
+
+# RUN: ld.lld -r %p/Inputs/mips-options.o -o %t.o
+# RUN: llvm-readobj -t %t.o | FileCheck %s
+
+# REQUIRES: mips
+
+# CHECK: Section: .MIPS.options