[llvm] r348349 - Recommit r348243 - "[llvm-mc] - Do not crash when referencing undefined debug sections."

[George Rimar via llvm-commits]

Author: grimar
Date: Wed Dec  5 02:43:58 2018
New Revision: 348349

URL: http://llvm.org/viewvc/llvm-project?rev=348349&view=rev
Log:
Recommit r348243 - "[llvm-mc] - Do not crash when referencing undefined debug sections."

The patch triggered an unrelated msan issue: LayoutOrder variable was not initialized.
(http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/26794/steps/check-llvm%20msan/logs/stdio)
It was fixed.

Original commit message:
MC has code that pre-creates few debug sections:
https://github.com/llvm-mirror/llvm/blob/master/lib/MC/MCObjectFileInfo.cpp#L396

If users code has a reference to such section but does not redefine it,
MC code currently asserts, because still thinks they are normally defined.

The patch fixes the issue.

Differential revision: https://reviews.llvm.org/D55173
----
Modified : /llvm/trunk/lib/MC/ELFObjectWriter.cpp
Added : /llvm/trunk/test/MC/ELF/undefined-debug.s


Added:
    llvm/trunk/test/MC/ELF/undefined-debug.s
      - copied unchanged from r348247, llvm/trunk/test/MC/ELF/undefined-debug.s
Modified:
    llvm/trunk/lib/MC/ELFObjectWriter.cpp
    llvm/trunk/lib/MC/MCFragment.cpp

Modified: llvm/trunk/lib/MC/ELFObjectWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/ELFObjectWriter.cpp?rev=348349&r1=348348&r2=348349&view=diff
==============================================================================
--- llvm/trunk/lib/MC/ELFObjectWriter.cpp (original)
+++ llvm/trunk/lib/MC/ELFObjectWriter.cpp Wed Dec  5 02:43:58 2018
@@ -669,6 +669,20 @@ void ELFWriter::computeSymbolTable(
     } else {
       const MCSectionELF &Section =
           static_cast<const MCSectionELF &>(Symbol.getSection());
+
+      // We may end up with a situation when section symbol is technically
+      // defined, but should not be. That happens because we explicitly
+      // pre-create few .debug_* sections to have accessors.
+      // And if these sections were not really defined in the code, but were
+      // referenced, we simply error out.
+      if (!Section.isRegistered()) {
+        assert(static_cast<const MCSymbolELF &>(Symbol).getType() ==
+               ELF::STT_SECTION);
+        Ctx.reportError(SMLoc(),
+                        "Undefined section reference: " + Symbol.getName());
+        continue;
+      }
+
       if (Mode == NonDwoOnly && isDwoSection(Section))
         continue;
       MSD.SectionIndex = SectionIndexMap.lookup(&Section);

Modified: llvm/trunk/lib/MC/MCFragment.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCFragment.cpp?rev=348349&r1=348348&r2=348349&view=diff
==============================================================================
--- llvm/trunk/lib/MC/MCFragment.cpp (original)
+++ llvm/trunk/lib/MC/MCFragment.cpp Wed Dec  5 02:43:58 2018
@@ -238,7 +238,7 @@ MCFragment::~MCFragment() = default;
 MCFragment::MCFragment(FragmentType Kind, bool HasInstructions,
                        MCSection *Parent)
     : Kind(Kind), HasInstructions(HasInstructions), Parent(Parent),
-      Atom(nullptr), Offset(~UINT64_C(0)) {
+      Atom(nullptr), Offset(~UINT64_C(0)), LayoutOrder(0) {
   if (Parent && !isDummy())
     Parent->getFragmentList().push_back(this);
 }