[LLD] [COFF] Fix reporting duplicate errors for absolute symbols

[mstorsjo]

Summary

Previously this caused crashes in the reportDuplicate method.

A DefinedAbsolute doesn't have any InputFile attached to it, so we can't report the file for the original symbol.

We could add an InputFile argument to SymbolTable::addAbsolute only for the sake of error reporting, but even then it'd be assymetrical, only pointing out the file containing the new conflicting definition, not the original one.

[ruiu]

LGTM

lld/COFF/SymbolTable.cpp

static std::string getSourceLocationObj(ObjFile *file, SectionChunk *sc,
   if (fileLine)
     os << fileLine->first << ":" << fileLine->second << "\n>>>            ";
   os << toString(file);
   return os.str();
 }
 
 static std::string getSourceLocation(InputFile *file, SectionChunk *sc,
                                      uint32_t offset, StringRef name) {
+  if (!file)
+    return "";
   if (auto *o = dyn_cast<ObjFile>(file))
     return getSourceLocationObj(o, sc, offset, name);
   if (auto *b = dyn_cast<BitcodeFile>(file))
     return getSourceLocationBitcode(b);
   return "\n>>> defined at " + toString(file);
 }
 
 // Construct and print an error message in the form of:
 //
 //   lld-link: error: duplicate symbol: foo
 //   >>> defined at bar.c:30
 //   >>>            bar.o
 //   >>> defined at baz.c:563
 //   >>>            baz.o
 void SymbolTable::reportDuplicate(Symbol *existing, InputFile *newFile,
                                   SectionChunk *newSc,
                                   uint32_t newSectionOffset) {
   std::string msg;
   llvm::raw_string_ostream os(msg);
   os << "duplicate symbol: " << toString(*existing);
 
-  DefinedRegular *d = cast<DefinedRegular>(existing);
+  DefinedRegular *d = dyn_cast<DefinedRegular>(existing);
   if (d && isa<ObjFile>(d->getFile())) {
     os << getSourceLocation(d->getFile(), d->getChunk(), d->getValue(),
                             existing->getName());
   } else {
     os << getSourceLocation(existing->getFile(), nullptr, 0, "");
   }
   os << getSourceLocation(newFile, newSc, newSectionOffset,
                           existing->getName());

lld/test/COFF/duplicate-absolute.s

+// REQUIRES: x86
+// RUN: llvm-mc -triple x86_64-windows-msvc -filetype obj -o %t.obj %s
+// RUN: echo -e ".globl myabsolute\nmyabsolute = 0" > %t.dupl.s
+// RUN: llvm-mc -triple x86_64-windows-msvc -filetype obj -o %t.dupl.obj %t.dupl.s
+// RUN: not lld-link /out:%t.exe %t.obj %t.dupl.obj 2>&1 | FileCheck %s
+
+// CHECK: error: duplicate symbol: myabsolute
+
+.globl myabsolute
+myabsolute = 0
+
+.globl entry
+entry:
+    ret