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

llvm-svn: 348349

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/MC/MCFragment.cpp b/llvm/lib/MC/MCFragment.cpp
index 0ebcf21a422..f2e08184c72 100644
--- a/llvm/lib/MC/MCFragment.cpp
+++ b/llvm/lib/MC/MCFragment.cpp
@@ -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);
 }