DWARF: Ignore a compile unit with no abbreviations (#2678)

Such a module can't have valid DIEs, since we have no way to
interpret them.

Also check if DWARF sections from LLVM have contents -
when they are empty the section may exist but have a null
for its data.

Fixes #2673

5 files changed, 7 insertions, 1 deletions

diff --git a/src/wasm/wasm-debug.cpp b/src/wasm/wasm-debug.cpp
index 50a04a6e6..286b63e69 100644
--- a/src/wasm/wasm-debug.cpp
+++ b/src/wasm/wasm-debug.cpp
@@ -56,7 +56,7 @@ struct BinaryenDWARFInfo {
   BinaryenDWARFInfo(const Module& wasm) {
     // Get debug sections from the wasm.
     for (auto& section : wasm.userSections) {
-      if (Name(section.name).startsWith(".debug_")) {
+      if (Name(section.name).startsWith(".debug_") && section.data.data()) {
         // TODO: efficiency
         sections[section.name.substr(1)] = llvm::MemoryBuffer::getMemBufferCopy(
           llvm::StringRef(section.data.data(), section.data.size()));
diff --git a/test/passes/dwarf_unit_with_no_abbrevs_noprint.bin.txt b/test/passes/dwarf_unit_with_no_abbrevs_noprint.bin.txt
new file mode 100644
index 000000000..e69de29bb
--- /dev/null
+++ b/test/passes/dwarf_unit_with_no_abbrevs_noprint.bin.txt
diff --git a/test/passes/dwarf_unit_with_no_abbrevs_noprint.passes b/test/passes/dwarf_unit_with_no_abbrevs_noprint.passes
new file mode 100644
index 000000000..48ea00769
--- /dev/null
+++ b/test/passes/dwarf_unit_with_no_abbrevs_noprint.passes
@@ -0,0 +1 @@
+roundtrip_g
diff --git a/test/passes/dwarf_unit_with_no_abbrevs_noprint.wasm b/test/passes/dwarf_unit_with_no_abbrevs_noprint.wasm
new file mode 100644
index 000000000..bf50db775
--- /dev/null
+++ b/test/passes/dwarf_unit_with_no_abbrevs_noprint.wasm
diff --git a/third_party/llvm-project/DWARFVisitor.cpp b/third_party/llvm-project/DWARFVisitor.cpp
index 44bb33b47..ba3d1e0c5 100644
--- a/third_party/llvm-project/DWARFVisitor.cpp
+++ b/third_party/llvm-project/DWARFVisitor.cpp
@@ -59,6 +59,11 @@ template <typename T> void DWARFYAML::VisitorImpl<T>::traverseDebugInfo() {
            DebugInfo.AbbrevDecls[AbbrevEnd].Code) {
       AbbrevEnd++;
     }
+    // XXX BINARYEN If there are no abbreviations, there is nothing to
+    //              do in this unit.
+    if (AbbrevStart == AbbrevEnd) {
+      continue;
+    }
     onStartCompileUnit(Unit);
     if (Unit.Entries.empty()) { // XXX BINARYEN
       continue;