Contract DacStreams

This contract is for getting information from the streams embedded into a dump file as it crashes

APIs of contract

csharp

// Return string corresponding to type system data structure if it exists, or null otherwise
string StringFromEEAddress(TargetPointer address);

Version 1

Global variables used

Global Name	Type	Purpose
MiniMetaDataBuffAddress	TargetPointer	Identify where the mini metadata stream exists
MiniMetaDataBuffMaxSize	uint	Identify where the size of the mini metadata stream

Magic numbers

Name	Value
MiniMetadataSignature	0x6d727473
EENameStreamSignature	0x614e4545

The format of the MiniMetadataStream begins with a Streams header, which has 3 fields

Field	Type	Offset	Meaning
MiniMetadataSignature	uint	0	Magic value used to identify that there are streams
TotalSize	uint	4	Total size of the entire set of MiniMetadata streams including this header
Count of Streams	uint	8	Number of streams in the MiniMetadata

The concept is that each stream simply follows the previous stream in the buffer. There is no padding, so the data is not expected to be aligned within the buffer. NOTE: At the moment there is only 1 supported stream type, so Count of Streams can only be 1.

The EENameStream is structured as a header, plus a series of null-terminated utf8 strings, and pointers.

The EENameStream header

Field	Type	Offset	Meaning
EENameStreamSignature	uint	0	Magic value used to identify that the bytes immediately following are an `EENameStream`
CountOfNames	uint	4	Number of names encoded

EENameStream entry

Field	Type	Offset	Meaning
Pointer	pointer	0	Pointer to type system structure
String	null-terminated UTF-8 sting	4 or 8 based on target pointer size	Pointer to type system structure

Following the EENameStream header, there are CountOfNames entries. Each entry begins with a target pointer sized block which identifies a particular type system data structure, followed by a utf8 encoded null-terminated string.

csharp

string StringFromEEAddress(TargetPointer address)
{
    TargetPointer miniMetaDataBuffAddress = _target.Read<uint>(_target.ReadGlobalPointer("MiniMetaDataBuffAddress"));
    uint miniMetaDataBuffMaxSize = _target.Read<uint>(_target.ReadGlobalPointer("MiniMetaDataBuffMaxSize"));

    // Parse MiniMetadataStream according the the format described above to produce a dictionary from pointer to string from the EENameStream.
    // Then lookup in the dictionary, to produce a result if it was present in the table.
    // In general, since this api is intended for fallback scenarios, implementations of this api should attempt
    // to return null instead of producing errors.
    // Since in normal execution of the runtime no stream is constructed, it is normal when examining full dumps and live process state without a stream encoded.
}