[llvm-dwarfdump] - Print an error message if section decompression failed.

llvm-dwarfdump currently prints no message if decompression fails 
for some reason. I noticed that during work on one of LLD patches 
where LLD produced an broken output. It was a bit confusing to see
no output for section dumped and no any error message at all.

Patch adds error message for such cases.

Differential revision: https://reviews.llvm.org/D32865

llvm-svn: 302221

llvm/include/llvm/DebugInfo/DWARF/DWARFContext.h

@@ -310,6 +310,9 @@ class DWARFContextInMemory : public DWARFContext {
 
   StringRef *MapSectionToMember(StringRef Name);
 
+  Error maybeDecompress(const object::SectionRef &Sec, StringRef Name,
+                        StringRef &Data);
+
 public:
   DWARFContextInMemory(const object::ObjectFile &Obj,
     const LoadedObjectInfo *L = nullptr);

llvm/lib/DebugInfo/DWARF/DWARFContext.cpp

@@ -957,6 +957,26 @@ static bool isRelocScattered(const object::ObjectFile &Obj,
   return MachObj->isRelocationScattered(RelocInfo);
 }
 
+Error DWARFContextInMemory::maybeDecompress(const SectionRef &Sec,
+                                            StringRef Name, StringRef &Data) {
+  if (!Decompressor::isCompressed(Sec))
+    return Error::success();
+
+  Expected<Decompressor> Decompressor =
+      Decompressor::create(Name, Data, IsLittleEndian, AddressSize == 8);
+  if (!Decompressor)
+    return Decompressor.takeError();
+
+  SmallString<32> Out;
+  if (auto Err = Decompressor->decompress(Out))
+    return Err;
+
+  UncompressedSections.emplace_back(std::move(Out));
+  Data = UncompressedSections.back();
+
+  return Error::success();
+}
+
 DWARFContextInMemory::DWARFContextInMemory(const object::ObjectFile &Obj,
     const LoadedObjectInfo *L)
     : IsLittleEndian(Obj.isLittleEndian()),
@@ -980,16 +1000,11 @@ DWARFContextInMemory::DWARFContextInMemory(const object::ObjectFile &Obj,
     if (!L || !L->getLoadedSectionContents(*RelocatedSection,data))
       Section.getContents(data);
 
-    if (Decompressor::isCompressed(Section)) {
-      Expected<Decompressor> Decompressor =
-          Decompressor::create(name, data, IsLittleEndian, AddressSize == 8);
-      if (!Decompressor)
-        continue;
-      SmallString<32> Out;
-      if (auto Err = Decompressor->decompress(Out))
-        continue;
-      UncompressedSections.emplace_back(std::move(Out));
-      data = UncompressedSections.back();
+    if (auto Err = maybeDecompress(Section, name, data)) {
+      errs() << "error: failed to decompress '" + name + "', " +
+                    toString(std::move(Err))
+             << '\n';
+      continue;
     }
 
     // Compressed sections names in GNU style starts from ".z",

llvm/test/DebugInfo/dwarfdump-decompression-error.test

@@ -0,0 +1,15 @@
+REQUIRES: zlib
+
+// dwarfdump-decompression-error.elf-x86-64 is prepared using following
+// source code and invocation:
+// test.cpp:
+// int main() { return 0; }
+//
+// gcc test.cpp -o out -g -Wl,--compress-debug-sections,zlib
+//
+// After that result object was modified manually. One random byte in compressed
+// content of .debug_info section was changed to 0xff. That breaks normal 
+// decompression flow in runtime.
+RUN: llvm-dwarfdump %p/Inputs/dwarfdump-decompression-error.elf-x86-64 2>&1 | FileCheck %s
+
+CHECK: error: failed to decompress '.debug_info', zlib error: Z_DATA_ERROR