[ELF] Fix error reporting for synthetic sections

Synthetic sections don't belong to any input file, but still they
are input sections. Whenever problem occurs with relocations in
these sections lld crashes in error reporting, trying to print
input file name.

Differential revision: https://reviews.llvm.org/D30889

llvm-svn: 297711

lld/ELF/InputSection.cpp

@@ -172,6 +172,11 @@ InputSectionBase *InputSectionBase::getLinkOrderDep() const {
 // Returns a source location string. Used to construct an error message.
 template <class ELFT>
 std::string InputSectionBase::getLocation(uint64_t Offset) {
+  // We don't have file for synthetic sections.
+  if (getFile<ELFT>() == nullptr)
+    return (Config->OutputFile + ":(" + Name + "+0x" + utohexstr(Offset) + ")")
+        .str();
+
   // First check if we can get desired values from debugging information.
   std::string LineInfo = getFile<ELFT>()->getLineInfo(this, Offset);
   if (!LineInfo.empty())