From 28b2d0c96f2277b87f50dde6e3e9d6273617b1e6 Mon Sep 17 00:00:00 2001
From: Jonas Devlieghere <jonas@devlieghere.com>
Date: Thu, 21 Sep 2017 10:28:33 +0000
Subject: [PATCH] [dsymutil] Don't resolve DIE reference to NULL DIE.

This patch prevents dsymutil from resolving a reference to a NULL DIE
when a bogus reference happens to be coincidentally referencing a NULL
DIE. Now this is detected as an invalid reference and a warning is
printed.

Fixes: https://bugs.llvm.org/show_bug.cgi?id=33873

Differential revision: https://reviews.llvm.org/D38078

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313872 91177308-0d34-0410-b5e6-96231b3b80d8
---
 test/tools/dsymutil/Inputs/null_die.o | Bin 0 -> 2216 bytes
 test/tools/dsymutil/null-die.test     |  41 ++++++++++++++++++++++++++
 tools/dsymutil/DwarfLinker.cpp        |   8 +++--
 3 files changed, 47 insertions(+), 2 deletions(-)
 create mode 100644 test/tools/dsymutil/Inputs/null_die.o
 create mode 100644 test/tools/dsymutil/null-die.test

diff --git a/test/tools/dsymutil/Inputs/null_die.o b/test/tools/dsymutil/Inputs/null_die.o
new file mode 100644
index 0000000000000000000000000000000000000000..1abde8676a3d2062f1cf9fc08fc1ad8d449cc406
GIT binary patch
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literal 0
HcmV?d00001

diff --git a/test/tools/dsymutil/null-die.test b/test/tools/dsymutil/null-die.test
new file mode 100644
index 00000000000..253c23c6058
--- /dev/null
+++ b/test/tools/dsymutil/null-die.test
@@ -0,0 +1,41 @@
+#RUN: llvm-dsymutil -f -oso-prepend-path=%p/Inputs/ -y %s -no-output 2>&1 \
+#RUN:   |  FileCheck %s
+
+# CHECK: warning: could not find referenced DIE
+
+# We've modified the DW_AT_abstract_origin offset to reference a NULL DIE.
+#
+# Source:
+#
+#   void f1() {}
+#   __attribute__((always_inline)) void f2() {
+#     f1();
+#   }
+#   int main() {
+#     f2();
+#   }
+#
+# Compile with:
+#
+#   $ clang -g null_die.c -O0 -S -o null_die.s
+#
+#   Manually patch the DW_AT_abstract_origin to point to a NULL DIE.
+#
+#   $ llvm-mc -triple x86_64-apple-darwin -filetype=obj -o null_die.o null_die.s
+#
+# To generate the debug map:
+#
+#   $ ld -arch x86_64 -macosx_version_min 10.13.0 -lSystem null_die.o -o null_die
+#   $ llvm-dsymutil -dump-debug-map null_die
+
+---
+triple:          'x86_64-apple-darwin'
+binary-path:     null_die
+objects:
+  - filename:        /null_die.o
+    timestamp:       1505928022
+    symbols:
+      - { sym: _main, objAddr: 0x0000000000000020, binAddr: 0x0000000100000F10, size: 0x0000000D }
+      - { sym: _f1, objAddr: 0x0000000000000000, binAddr: 0x0000000100000EF0, size: 0x00000010 }
+      - { sym: _f2, objAddr: 0x0000000000000010, binAddr: 0x0000000100000F00, size: 0x00000010 }
+...
diff --git a/tools/dsymutil/DwarfLinker.cpp b/tools/dsymutil/DwarfLinker.cpp
index 3ab3c7f5720..69adf379ca0 100644
--- a/tools/dsymutil/DwarfLinker.cpp
+++ b/tools/dsymutil/DwarfLinker.cpp
@@ -1495,8 +1495,12 @@ static DWARFDie resolveDIEReference(
   uint64_t RefOffset = *RefValue.getAsReference();
 
   if ((RefCU = getUnitForOffset(Units, RefOffset)))
-    if (const auto RefDie = RefCU->getOrigUnit().getDIEForOffset(RefOffset))
-      return RefDie;
+    if (const auto RefDie = RefCU->getOrigUnit().getDIEForOffset(RefOffset)) {
+      // In a file with broken references, an attribute might point to a NULL
+      // DIE.
+      if(!RefDie.isNULL())
+        return RefDie;
+    }
 
   Linker.reportWarning("could not find referenced DIE", &DIE);
   return DWARFDie();
-- 
2.40.0