Exemple #1
0
        private bool WritePeToStream(MetadataWriter mdWriter, Func<Stream> getPeStream, Func<Stream> getPortablePdbStreamOpt, PdbWriter nativePdbWriterOpt)
        {
            // TODO: we can precalculate the exact size of IL stream
            var ilWriter = new BlobBuilder(32 * 1024);
            var metadataWriter = new BlobBuilder(16 * 1024);
            var mappedFieldDataWriter = new BlobBuilder();
            var managedResourceWriter = new BlobBuilder(1024);

            var debugMetadataWriterOpt = (getPortablePdbStreamOpt != null) ? new BlobBuilder(16 * 1024) : null;

            nativePdbWriterOpt?.SetMetadataEmitter(mdWriter);

            // Since we are producing a full assembly, we should not have a module version ID
            // imposed ahead-of time. Instead we will compute a deterministic module version ID
            // based on the contents of the generated stream.
            Debug.Assert(_properties.PersistentIdentifier == default(Guid));

            int sectionCount = 1;
            if (_properties.RequiresStartupStub) sectionCount++; //.reloc
            if (!IteratorHelper.EnumerableIsEmpty(_nativeResourcesOpt) || _nativeResourceSectionOpt != null) sectionCount++; //.rsrc;

            int sizeOfPeHeaders = ComputeSizeOfPeHeaders(sectionCount);
            int textSectionRva = BitArithmeticUtilities.Align(sizeOfPeHeaders, _properties.SectionAlignment);

            int moduleVersionIdOffsetInMetadataStream;
            int methodBodyStreamRva = textSectionRva + OffsetToILStream;

            int entryPointToken;
            MetadataSizes metadataSizes;
            mdWriter.SerializeMetadataAndIL(
                metadataWriter,
                debugMetadataWriterOpt,
                nativePdbWriterOpt,
                ilWriter,
                mappedFieldDataWriter,
                managedResourceWriter,
                methodBodyStreamRva,
                mdSizes => CalculateMappedFieldDataStreamRva(textSectionRva, mdSizes),
                out moduleVersionIdOffsetInMetadataStream,
                out entryPointToken,
                out metadataSizes);

            ContentId nativePdbContentId;
            if (nativePdbWriterOpt != null)
            {
                if (entryPointToken != 0)
                {
                    nativePdbWriterOpt.SetEntryPoint((uint)entryPointToken);
                }

                var assembly = mdWriter.Module.AsAssembly;
                if (assembly != null && assembly.Kind == OutputKind.WindowsRuntimeMetadata)
                {
                    // Dev12: If compiling to winmdobj, we need to add to PDB source spans of
                    //        all types and members for better error reporting by WinMDExp.
                    nativePdbWriterOpt.WriteDefinitionLocations(mdWriter.Module.GetSymbolToLocationMap());
                }
                else
                {
#if DEBUG
                    // validate that all definitions are writable
                    // if same scenario would happen in an winmdobj project
                    nativePdbWriterOpt.AssertAllDefinitionsHaveTokens(mdWriter.Module.GetSymbolToLocationMap());
#endif
                }

                nativePdbContentId = nativePdbWriterOpt.GetContentId();

                // the writer shall not be used after this point for writing:
                nativePdbWriterOpt = null;
            }
            else
            {
                nativePdbContentId = default(ContentId);
            }
            
            // write to Portable PDB stream:
            ContentId portablePdbContentId;
            Stream portablePdbStream = getPortablePdbStreamOpt?.Invoke();
            if (portablePdbStream != null)
            {
                debugMetadataWriterOpt.WriteTo(portablePdbStream);

                if (_deterministic)
                {
                    portablePdbContentId = ContentId.FromHash(CryptographicHashProvider.ComputeSha1(portablePdbStream));
                }
                else
                {
                    portablePdbContentId = new ContentId(Guid.NewGuid().ToByteArray(), BitConverter.GetBytes(_timeStamp));
                }
            }
            else
            {
                portablePdbContentId = default(ContentId);
            }

            // Only the size of the fixed part of the debug table goes here.
            DirectoryEntry debugDirectory = default(DirectoryEntry);
            DirectoryEntry importTable = default(DirectoryEntry);
            DirectoryEntry importAddressTable = default(DirectoryEntry);
            int entryPointAddress = 0;

            if (EmitPdb)
            {
                debugDirectory = new DirectoryEntry(textSectionRva + ComputeOffsetToDebugTable(metadataSizes), ImageDebugDirectoryBaseSize);
            }

            if (_properties.RequiresStartupStub)
            {
                importAddressTable = new DirectoryEntry(textSectionRva, SizeOfImportAddressTable);
                entryPointAddress = CalculateMappedFieldDataStreamRva(textSectionRva, metadataSizes) - (_is32bit ? 6 : 10); // TODO: constants
                importTable = new DirectoryEntry(textSectionRva + ComputeOffsetToImportTable(metadataSizes), (_is32bit ? 66 : 70) + 13); // TODO: constants
            }

            var corHeaderDirectory = new DirectoryEntry(textSectionRva + SizeOfImportAddressTable, size: CorHeaderSize);

            long ntHeaderTimestampPosition;
            long metadataPosition;

            List<SectionHeader> sectionHeaders = CreateSectionHeaders(metadataSizes, sectionCount);

            CoffHeader coffHeader;
            NtHeader ntHeader;
            FillInNtHeader(sectionHeaders, entryPointAddress, corHeaderDirectory, importTable, importAddressTable, debugDirectory, out coffHeader, out ntHeader);

            Stream peStream = getPeStream();
            if (peStream == null)
            {
                return false;
            }

            WriteHeaders(peStream, ntHeader, coffHeader, sectionHeaders, out ntHeaderTimestampPosition);

            WriteTextSection(
                peStream,
                sectionHeaders[0],
                importTable.RelativeVirtualAddress,
                importAddressTable.RelativeVirtualAddress,
                entryPointToken,
                metadataWriter,
                ilWriter,
                mappedFieldDataWriter,
                managedResourceWriter,
                metadataSizes,
                nativePdbContentId,
                portablePdbContentId,
                out metadataPosition);

            var resourceSection = sectionHeaders.FirstOrDefault(s => s.Name == ResourceSectionName);
            if (resourceSection != null)
            {
                WriteResourceSection(peStream, resourceSection);
            }

            var relocSection = sectionHeaders.FirstOrDefault(s => s.Name == RelocationSectionName);
            if (relocSection != null)
            {
                WriteRelocSection(peStream, relocSection, entryPointAddress);
            }

            if (_deterministic)
            {
                var mvidPosition = metadataPosition + moduleVersionIdOffsetInMetadataStream;
                WriteDeterministicGuidAndTimestamps(peStream, mvidPosition, ntHeaderTimestampPosition);
            }

            return true;
        }
Exemple #2
0
        private void WriteTextSection(
            Stream peStream,
            SectionHeader textSection,
            int importTableRva,
            int importAddressTableRva,
            int entryPointToken,
            BlobBuilder metadataWriter,
            BlobBuilder ilWriter,
            BlobBuilder mappedFieldDataWriter,
            BlobBuilder managedResourceWriter,
            MetadataSizes metadataSizes,
            ContentId nativePdbContentId,
            ContentId portablePdbContentId,
            out long metadataPosition)
        {
            // TODO: zero out all bytes:
            peStream.Position = textSection.PointerToRawData;

            if (_properties.RequiresStartupStub)
            {
                WriteImportAddressTable(peStream, importTableRva);
            }

            var corHeader = CreateCorHeader(metadataSizes, textSection.RelativeVirtualAddress, entryPointToken);
            WriteCorHeader(peStream, corHeader);

            // IL:
            ilWriter.Align(4);
            ilWriter.WriteTo(peStream);

            // metadata:
            metadataPosition = peStream.Position;
            Debug.Assert(metadataWriter.Length % 4 == 0);
            metadataWriter.WriteTo(peStream);

            // managed resources:
            Debug.Assert(managedResourceWriter.Length % 4 == 0);
            managedResourceWriter.WriteTo(peStream);

            // strong name signature:
            WriteSpaceForHash(peStream, metadataSizes.StrongNameSignatureSize);

            if (EmitPdb)
            {
                WriteDebugTable(peStream, textSection, nativePdbContentId, portablePdbContentId, metadataSizes);
            }

            if (_properties.RequiresStartupStub)
            {
                WriteImportTable(peStream, importTableRva, importAddressTableRva);
                WriteNameTable(peStream);
                WriteRuntimeStartupStub(peStream, importAddressTableRva);
            }

            // mapped field data:            
            mappedFieldDataWriter.WriteTo(peStream);

            // TODO: zero out all bytes:
            int alignedPosition = textSection.PointerToRawData + textSection.SizeOfRawData;
            if (peStream.Position != alignedPosition)
            {
                peStream.Position = alignedPosition - 1;
                peStream.WriteByte(0);
            }
        }
Exemple #3
0
        private void WriteDebugTable(Stream peStream, SectionHeader textSection, ContentId nativePdbContentId, ContentId portablePdbContentId, MetadataSizes metadataSizes)
        {
            Debug.Assert(nativePdbContentId.IsDefault ^ portablePdbContentId.IsDefault);

            var writer = new BlobBuilder();

            // characteristics:
            writer.WriteUInt32(0);

            // PDB stamp & version
            if (portablePdbContentId.IsDefault)
            {
                writer.WriteBytes(nativePdbContentId.Stamp);
                writer.WriteUInt32(0);
            }
            else
            {
                writer.WriteBytes(portablePdbContentId.Stamp);
                writer.WriteUInt32('P' << 24 | 'M' << 16 | 0x00 << 8 | 0x01);
            }
            
            // type: 
            const int ImageDebugTypeCodeView = 2;
            writer.WriteUInt32(ImageDebugTypeCodeView);

            // size of data:
            writer.WriteUInt32((uint)ComputeSizeOfDebugDirectoryData());

            uint dataOffset = (uint)ComputeOffsetToDebugTable(metadataSizes) + ImageDebugDirectoryBaseSize;

            // PointerToRawData (RVA of the data):
            writer.WriteUInt32((uint)textSection.RelativeVirtualAddress + dataOffset);

            // AddressOfRawData (position of the data in the PE stream):
            writer.WriteUInt32((uint)textSection.PointerToRawData + dataOffset);

            writer.WriteByte((byte)'R');
            writer.WriteByte((byte)'S');
            writer.WriteByte((byte)'D');
            writer.WriteByte((byte)'S');

            // PDB id:
            writer.WriteBytes(nativePdbContentId.Guid ?? portablePdbContentId.Guid);

            // age
            writer.WriteUInt32(PdbWriter.Age);

            // UTF-8 encoded zero-terminated path to PDB
            writer.WriteUTF8(_pdbPathOpt);
            writer.WriteByte(0);

            writer.WriteTo(peStream);
            writer.Free();
        }
        private void WriteDebugTable(Stream peStream, ContentId nativePdbContentId, MetadataSizes metadataSizes)
        {
            if (!EmitPdb)
            {
                return;
            }

            var writer = new BlobWriter();

            // characteristics:
            writer.WriteUint(0);

            // PDB stamp
            writer.WriteBytes(nativePdbContentId.Stamp);

            // version
            writer.WriteUint(0);

            // type: 
            const int ImageDebugTypeCodeView = 2;
            writer.WriteUint(ImageDebugTypeCodeView);

            // size of data:
            writer.WriteUint((uint)ComputeSizeOfDebugDirectoryData());

            uint dataOffset = (uint)ComputeOffsetToDebugTable(metadataSizes) + ImageDebugDirectoryBaseSize;

            // PointerToRawData (RVA of the data):
            writer.WriteUint(_textSection.RelativeVirtualAddress + dataOffset);

            // AddressOfRawData (position of the data in the PE stream):
            writer.WriteUint(_textSection.PointerToRawData + dataOffset);

            writer.WriteByte((byte)'R');
            writer.WriteByte((byte)'S');
            writer.WriteByte((byte)'D');
            writer.WriteByte((byte)'S');

            // PDB id:
            writer.WriteBytes(nativePdbContentId.Guid);

            // age
            writer.WriteUint(PdbWriter.Age);

            // UTF-8 encoded zero-terminated path to PDB
            writer.WriteUTF8(_pdbPathOpt);
            writer.WriteByte(0);

            writer.WriteTo(peStream);
            writer.Free();
        }
        private void WriteTextSection(
            Stream peStream,
            CorHeader corHeader,
            BlobWriter metadataWriter,
            BlobWriter ilStream,
            BlobWriter mappedFieldDataWriter,
            BlobWriter managedResourceWriter,
            MetadataSizes metadataSizes,
            ContentId pdbContentId,
            out long metadataPosition)
        {
            peStream.Position = _textSection.PointerToRawData;
            if (_emitRuntimeStartupStub)
            {
                this.WriteImportAddressTable(peStream);
            }

            WriteCorHeader(peStream, corHeader);
            WriteIL(peStream, ilStream);

            metadataPosition = peStream.Position;
            WriteMetadata(peStream, metadataWriter);

            WriteManagedResources(peStream, managedResourceWriter);
            WriteSpaceForHash(peStream, (int)corHeader.StrongNameSignature.Size);
            WriteDebugTable(peStream, pdbContentId, metadataSizes);

            if (_emitRuntimeStartupStub)
            {
                WriteImportTable(peStream);
                WriteNameTable(peStream);
                WriteRuntimeStartupStub(peStream);
            }

            WriteMappedFieldData(peStream, mappedFieldDataWriter);
        }
        public static bool WritePeToStream(
            EmitContext context,
            CommonMessageProvider messageProvider,
            Func <Stream> getPeStream,
            Func <Stream> getPortablePdbStreamOpt,
            PdbWriter nativePdbWriterOpt,
            string pdbPathOpt,
            bool allowMissingMethodBodies,
            bool isDeterministic,
            CancellationToken cancellationToken)
        {
            // If PDB writer is given, we have to have PDB path.
            Debug.Assert(nativePdbWriterOpt == null || pdbPathOpt != null);

            var mdWriter = FullMetadataWriter.Create(context, messageProvider, allowMissingMethodBodies, isDeterministic, getPortablePdbStreamOpt != null, cancellationToken);

            var properties = context.Module.Properties;

            nativePdbWriterOpt?.SetMetadataEmitter(mdWriter);

            // Since we are producing a full assembly, we should not have a module version ID
            // imposed ahead-of time. Instead we will compute a deterministic module version ID
            // based on the contents of the generated stream.
            Debug.Assert(properties.PersistentIdentifier == default(Guid));

            var ilBuilder = new BlobBuilder(32 * 1024);
            var mappedFieldDataBuilder = new BlobBuilder();
            var managedResourceBuilder = new BlobBuilder(1024);

            Blob mvidFixup;

            mdWriter.BuildMetadataAndIL(
                nativePdbWriterOpt,
                ilBuilder,
                mappedFieldDataBuilder,
                managedResourceBuilder,
                out mvidFixup);

            MethodDefinitionHandle entryPointHandle;
            MethodDefinitionHandle debugEntryPointHandle;

            mdWriter.GetEntryPoints(out entryPointHandle, out debugEntryPointHandle);

            if (!debugEntryPointHandle.IsNil)
            {
                nativePdbWriterOpt?.SetEntryPoint((uint)MetadataTokens.GetToken(debugEntryPointHandle));
            }

            if (nativePdbWriterOpt != null)
            {
                var assembly = mdWriter.Module.AsAssembly;
                if (assembly != null && assembly.Kind == OutputKind.WindowsRuntimeMetadata)
                {
                    // Dev12: If compiling to winmdobj, we need to add to PDB source spans of
                    //        all types and members for better error reporting by WinMDExp.
                    nativePdbWriterOpt.WriteDefinitionLocations(mdWriter.Module.GetSymbolToLocationMap());
                }
                else
                {
#if DEBUG
                    // validate that all definitions are writable
                    // if same scenario would happen in an winmdobj project
                    nativePdbWriterOpt.AssertAllDefinitionsHaveTokens(mdWriter.Module.GetSymbolToLocationMap());
#endif
                }
            }

            Stream peStream = getPeStream();
            if (peStream == null)
            {
                return(false);
            }

            ContentId nativePdbContentId = nativePdbWriterOpt?.GetContentId() ?? default(ContentId);

            // the writer shall not be used after this point for writing:
            nativePdbWriterOpt = null;

            var metadataSerializer = mdWriter.GetTypeSystemMetadataSerializer();

            var peBuilder = new PEBuilder(
                machine: properties.Machine,
                sectionAlignment: properties.SectionAlignment,
                fileAlignment: properties.FileAlignment,
                imageBase: properties.BaseAddress,
                majorLinkerVersion: properties.LinkerMajorVersion,
                minorLinkerVersion: properties.LinkerMinorVersion,
                majorOperatingSystemVersion: 4,
                minorOperatingSystemVersion: 0,
                majorImageVersion: 0,
                minorImageVersion: 0,
                majorSubsystemVersion: properties.MajorSubsystemVersion,
                minorSubsystemVersion: properties.MinorSubsystemVersion,
                subsystem: properties.Subsystem,
                dllCharacteristics: properties.DllCharacteristics,
                imageCharacteristics: properties.ImageCharacteristics,
                sizeOfStackReserve: properties.SizeOfStackReserve,
                sizeOfStackCommit: properties.SizeOfStackCommit,
                sizeOfHeapReserve: properties.SizeOfHeapReserve,
                sizeOfHeapCommit: properties.SizeOfHeapCommit,
                deterministicIdProvider: isDeterministic ? new Func <BlobBuilder, ContentId>(content => ContentId.FromHash(CryptographicHashProvider.ComputeSha1(content))) : null);

            ContentId portablePdbContentId;
            if (mdWriter.EmitStandaloneDebugMetadata)
            {
                Debug.Assert(getPortablePdbStreamOpt != null);

                var debugMetadataBuilder    = new BlobBuilder();
                var debugMetadataSerializer = mdWriter.GetStandaloneDebugMetadataSerializer(metadataSerializer.MetadataSizes, debugEntryPointHandle);
                debugMetadataSerializer.SerializeMetadata(debugMetadataBuilder, peBuilder.IdProvider, out portablePdbContentId);

                // write to Portable PDB stream:
                Stream portablePdbStream = getPortablePdbStreamOpt();
                if (portablePdbStream != null)
                {
                    debugMetadataBuilder.WriteContentTo(portablePdbStream);
                }
            }
            else
            {
                portablePdbContentId = default(ContentId);
            }

            var peDirectoriesBuilder = new PEDirectoriesBuilder();

            peBuilder.AddManagedSections(
                peDirectoriesBuilder,
                metadataSerializer,
                ilBuilder,
                mappedFieldDataBuilder,
                managedResourceBuilder,
                CreateNativeResourceSectionSerializer(context.Module),
                CalculateStrongNameSignatureSize(context.Module),
                entryPointHandle,
                pdbPathOpt,
                nativePdbContentId,
                portablePdbContentId,
                properties.CorFlags);

            var       peBlob = new BlobBuilder();
            ContentId peContentId;
            peBuilder.Serialize(peBlob, peDirectoriesBuilder, out peContentId);

            // Patch MVID
            if (!mvidFixup.IsDefault)
            {
                var mvidWriter = new BlobWriter(mvidFixup);
                mvidWriter.WriteBytes(peContentId.Guid);
                Debug.Assert(mvidWriter.RemainingBytes == 0);
            }

            try
            {
                peBlob.WriteContentTo(peStream);
            }
            catch (Exception e) when(!(e is OperationCanceledException))
            {
                throw new PeWritingException(e);
            }

            return(true);
        }
Exemple #7
0
        public unsafe ContentId GetContentId()
        {
            if (_deterministic)
            {
                // Call to GetDebugInfo fails for SymWriter initialized using InitializeDeterministic.
                // We already have all the info we need though.

                // TODO (https://github.com/dotnet/roslyn/issues/926): calculate sha1 hash
                var id = new ContentId(
                    new byte[] { 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, },
                    new byte[] { 0x12, 0x12, 0x12, 0x12 });

                try
                {
                    Debug.Assert(BitConverter.IsLittleEndian);
                    ((ISymUnmanagedWriter6)_symWriter).SetSignature(BitConverter.ToUInt32(id.Stamp, 0), new Guid(id.Guid));
                }
                catch (Exception ex)
                {
                    throw new PdbWritingException(ex);
                }

                return(id);
            }

            // See symwrite.cpp - the data byte[] doesn't depend on the content of metadata tables or IL.
            // The writer only sets two values of the ImageDebugDirectory struct.
            //
            //   IMAGE_DEBUG_DIRECTORY *pIDD
            //
            //   if ( pIDD == NULL ) return E_INVALIDARG;
            //   memset( pIDD, 0, sizeof( *pIDD ) );
            //   pIDD->Type = IMAGE_DEBUG_TYPE_CODEVIEW;
            //   pIDD->SizeOfData = cTheData;

            ImageDebugDirectory debugDir = new ImageDebugDirectory();
            uint dataLength;

            try
            {
                _symWriter.GetDebugInfo(ref debugDir, 0, out dataLength, IntPtr.Zero);
            }
            catch (Exception ex)
            {
                throw new PdbWritingException(ex);
            }

            byte[] data = new byte[dataLength];
            fixed(byte *pb = data)
            {
                try
                {
                    _symWriter.GetDebugInfo(ref debugDir, dataLength, out dataLength, (IntPtr)pb);
                }
                catch (Exception ex)
                {
                    throw new PdbWritingException(ex);
                }
            }

            // Data has the following structure:
            // struct RSDSI
            // {
            //     DWORD dwSig;                 // "RSDS"
            //     GUID guidSig;                // GUID
            //     DWORD age;                   // age
            //     char szPDB[0];               // zero-terminated UTF8 file name passed to the writer
            // };
            const int GuidSize = 16;

            byte[] guidBytes = new byte[GuidSize];
            Buffer.BlockCopy(data, 4, guidBytes, 0, guidBytes.Length);

            // Retrieve the timestamp the PDB writer generates when creating a new PDB stream.
            // Note that ImageDebugDirectory.TimeDateStamp is not set by GetDebugInfo,
            // we need to go thru IPdbWriter interface to get it.
            uint stamp;
            uint age;

            ((IPdbWriter)_symWriter).GetSignatureAge(out stamp, out age);
            Debug.Assert(age == Age);

            Debug.Assert(BitConverter.IsLittleEndian);
            return(new ContentId(guidBytes, BitConverter.GetBytes(stamp)));
        }
Exemple #8
0
        public unsafe ContentId GetContentId()
        {
            if (_deterministic)
            {
                // Call to GetDebugInfo fails for SymWriter initialized using InitializeDeterministic.
                // We already have all the info we need though.

                // TODO (https://github.com/dotnet/roslyn/issues/926): calculate sha1 hash
                var id = new ContentId(
                    new byte[] { 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, 0x12, },
                    new byte[] { 0x12, 0x12, 0x12, 0x12 });

                try
                {
                    Debug.Assert(BitConverter.IsLittleEndian);
                    ((ISymUnmanagedWriter6)_symWriter).SetSignature(BitConverter.ToUInt32(id.Stamp, 0), new Guid(id.Guid));
                }
                catch (Exception ex)
                {
                    throw new PdbWritingException(ex);
                }

                return id;
            }

            // See symwrite.cpp - the data byte[] doesn't depend on the content of metadata tables or IL.
            // The writer only sets two values of the ImageDebugDirectory struct.
            // 
            //   IMAGE_DEBUG_DIRECTORY *pIDD
            // 
            //   if ( pIDD == NULL ) return E_INVALIDARG;
            //   memset( pIDD, 0, sizeof( *pIDD ) );
            //   pIDD->Type = IMAGE_DEBUG_TYPE_CODEVIEW;
            //   pIDD->SizeOfData = cTheData;
            
            ImageDebugDirectory debugDir = new ImageDebugDirectory();
            uint dataLength;

            try
            {
                _symWriter.GetDebugInfo(ref debugDir, 0, out dataLength, IntPtr.Zero);
            }
            catch (Exception ex)
            {
                throw new PdbWritingException(ex);
            }

            byte[] data = new byte[dataLength];
            fixed (byte* pb = data)
            {
                try
                {
                    _symWriter.GetDebugInfo(ref debugDir, dataLength, out dataLength, (IntPtr)pb);
                }
                catch (Exception ex)
                {
                    throw new PdbWritingException(ex);
                }
            }

            // Data has the following structure:
            // struct RSDSI                     
            // {
            //     DWORD dwSig;                 // "RSDS"
            //     GUID guidSig;                // GUID
            //     DWORD age;                   // age
            //     char szPDB[0];               // zero-terminated UTF8 file name passed to the writer
            // };
            const int GuidSize = 16;
            byte[] guidBytes = new byte[GuidSize];
            Buffer.BlockCopy(data, 4, guidBytes, 0, guidBytes.Length);

            // Retrieve the timestamp the PDB writer generates when creating a new PDB stream.
            // Note that ImageDebugDirectory.TimeDateStamp is not set by GetDebugInfo, 
            // we need to go thru IPdbWriter interface to get it.
            uint stamp;
            uint age;
            ((IPdbWriter)_symWriter).GetSignatureAge(out stamp, out age);
            Debug.Assert(age == Age);

            Debug.Assert(BitConverter.IsLittleEndian);
            return new ContentId(guidBytes, BitConverter.GetBytes(stamp));
        }