[Coverage] Ensure that coverage mapping data has an expected alignment in 'covmapping' files.

Coverage mapping data is organized in a sequence of blocks, each of which is expected
to be aligned by 8 bytes. This feature is used when reading those blocks, see
VersionedCovMapFuncRecordReader::readFunctionRecords(). If a misaligned covearge
mapping data has more than one block, it causes llvm-cov to fail.

Differential Revision: http://reviews.llvm.org/D20285

llvm-svn: 269887

llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp

@@ -491,6 +491,13 @@ static std::error_code loadTestingFormat(StringRef Data,
     return coveragemap_error::malformed;
   ProfileNames.create(Data.substr(0, ProfileNamesSize), Address);
   CoverageMapping = Data.substr(ProfileNamesSize);
+  // Skip the padding bytes because coverage map data has an alignment of 8.
+  if (CoverageMapping.size() < 1)
+    return coveragemap_error::truncated;
+  size_t Pad = alignmentAdjustment(CoverageMapping.data(), 8);
+  if (CoverageMapping.size() < Pad)
+    return coveragemap_error::malformed;
+  CoverageMapping = CoverageMapping.substr(Pad);
   return std::error_code();
 }
 

llvm/tools/llvm-cov/TestingSupport.cpp

@@ -88,7 +88,11 @@ int convertForTestingMain(int argc, const char *argv[]) {
   OS << "llvmcovmtestdata";
   encodeULEB128(ProfileNamesData.size(), OS);
   encodeULEB128(ProfileNamesAddress, OS);
-  OS << ProfileNamesData << CoverageMappingData;
+  OS << ProfileNamesData;
+  // Coverage mapping data is expected to have an alignment of 8.
+  for (unsigned Pad = OffsetToAlignment(OS.tell(), 8); Pad; --Pad)
+    OS.write(uint8_t(0));
+  OS << CoverageMappingData;
 
   return 0;
 }