[LLD][ELF] Fix --check-dynamic-relocations for 32-bit targets

[andrewng]

Summary

OutputSection::checkDynRelAddends() incorrectly reports an internal
linker error for large addends on 32-bit targets. This is caused by the
lack of sign extension in DynamicReloc::computeAddend() for 32-bit
addends.

[arichardson]

Change looks sensible to me but the test could do with some kind of explanation of what it's doing.

lld/test/ELF/arm-pie-relative.s

6

This test could do with a comment or some check lines?

[MaskRay]

lld/ELF/SyntheticSections.cpp

1568

lld/test/ELF/arm-pie-relative.s

6

Adding a llvm-readelf -x .got will make it more useful.

[andrewng]

Updated to address review comments and suggestions.

[MaskRay]

Looks great!

lld/ELF/SyntheticSections.cpp

int64_t DynamicReloc::computeAddend() const {
   switch (kind) {
   case AddendOnly:
     assert(sym == nullptr);
     return addend;
   case AgainstSymbol:
     assert(sym != nullptr);
     return addend;
   case AddendOnlyWithTargetVA:
-  case AgainstSymbolWithTargetVA:
-    return InputSection::getRelocTargetVA(inputSec->file, type, addend,
+  case AgainstSymbolWithTargetVA: {
+    int64_t ca = InputSection::getRelocTargetVA(inputSec->file, type, addend,
                                                 getOffset(), *sym, expr);
+    return config->is64 ? ca : SignExtend64<32>(ca);
+  }
   case MipsMultiGotPage:
     assert(sym == nullptr);
     return getMipsPageAddr(outputSec->addr) + addend;
   }
   llvm_unreachable("Unknown DynamicReloc::Kind enum");
 }
 
 uint32_t DynamicReloc::getSymIndex(SymbolTableBaseSection *symTab) const {

lld/test/ELF/arm-pie-relative.s

 // REQUIRES: arm
 // RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t.o
 // RUN: ld.lld %t.o --pie -o %t
 // RUN: llvm-readobj -r %t | FileCheck %s
 // RUN: llvm-readelf -x .got %t | FileCheck %s --check-prefix=GOT
+// RUN: ld.lld %t.o --pie --image-base=0x80000000 --check-dynamic-relocations -o /dev/null
 
 // Test that a R_ARM_GOT_BREL relocation with PIE results in a R_ARM_RELATIVE
 // dynamic relocation
  .syntax unified
  .text
  .global _start
 _start:
  .word sym(GOT)