An overview of the SSCLI Distribution Mark Lewin Microsoft Research

Stats for SSCLI Archive (approximate as of 27 March 2002) Packaged as single compressed file archive 1.9 million lines of code –1.15M of C and C++ –625K of C# –125K of CIL (intermediate language) –Smattering of assembly code 5900 source files (9700 total) –2900 tests Build output –1200 defined types –About 20 dynamically loadable libraries –About 22 executable programs

The Lay of the Land Four major areas in source code 1.Runtime “execution engine” 2.Frameworks 3.Compilers and tools 4.Portability layer, tests, and build infrastructure Other important points of interest –License –Documentation –Samples

Root Directory: License & Doc Shared source license –Allows for non-commercial redistribution of both binary and source, including modified versions –Simple restrictions (primarily non-commercial use) READFIRST.html –Points to relnotes.html with late breaking items –Points to docs/index.html Also important, but not included: –ECMA specifications –Microsoft.NET Frameworks SDK

Area #1: Execution Engine Heart of component-oriented infrastructure Converts metadata, resources, and CIL (on disk as PE/COFF image) into running code Great interoperability with “unmanaged code” JIT compilation and IL verification Cross-language exception handling Language-agnostic, object-capable, type system Automatic heap and stack management Dynamic code loading Evidence-based security (code access security)

Look For: PE Reading/Writing “Portable Executable” format –Based on PE/COFF (see ceefilegen for details) –Uses existing extension mechanism –Three kinds of CLI data: metadata, CIL instructions, resources Persistent packaging for types –Methods include stack frame size, types of local variables and parameters, pinned variable info, and exception handler table –Powerful metadata extensibility Logical components as “assemblies” –Enforced security boundary, see fusion for binding logic –Also contains refs to other assemblies and version info –Cryptographic “strong names” an option (required for sharing)

Look For: Metadata Facilities Metadata is heart of CLI execution model –Metadata interwoven with instruction set –Read-only PE pages shared between processes –Tokens used for addressing metadata –Data stored in tables (heaps when variable length) –Tokens are concatenated table + record number –Optimized for load time at expense of generation complexity/speed; compact within these parameters Three levels of API –Reflection for managed code –Both internal and external API for C/C++, see md

Look For: CIL Basis for most managed code execution in the CLI Simple stack machine model – see vm directory Typeless opcodes defined in opcodes.def –Verifiable subset – see fjit directory for verification –Signed and unsigned via opcode, not type CIL code is JIT compiled to run under CLI management –Type layout, control, and dispatching Typed variable argument lists, dynamically typed pointers Tail calls, virtual dispatch, call via function pointer –Rich set of conversion operations, calling conventions, interop –Exception handling (two-pass) –Garbage collection

Area #2: Frameworks A “minimal toolkit” for the 21 st century programmer Base class library –Collections, arrays, strings, and other compound datatypes –Globalization and formatting –System services (threads, I/O, synchronization, etc.) –Security Floating point and extended arrays libraries Networking, regular expressions, and XML libraries Includes access to runtime infrastructure –Reflection and custom attributes –Remoting, unmanaged interop, serialization, and marshaling –AppDomains, Assemblies, GC, other execution engine features

Area #3: Compilers and Tools Full-featured C# compiler (also used in build) JScript compiler written entirely in C# Additional developer tools –clix, the shared source CLI program launcher –Assembly tools: resource compiler, assembly linker, metainfo metadata viewer, assembler, disassembler –Debuggers: cordbg managed debugger, plus a debug extension for working on managed code from C/C++

Interesting C# Features to Examine Unified type system (boxing) Extensible attributes Properties Events Indexers struct types Enumeration types Delegate types override Unsafe code Conditional methods Interop (parameter marshaling) Multi-dimensional arrays Operator overloading User-defined conversions Variable parameter lists ref and out parameters Unsigned types Decimal type Conditional compilation foreach statement Overflow checking Explicit interface implementations

Area #4: Build, Port, & Test Platform Adaptation Layer (PAL) in pal directory –System resources all consumed via PAL –Less than 250 partially complete Win32 APIs –Missing system features layered into PAL on any given platform –“PAL runtime” contains shared code for upper level tools Good specification can be found in pal_guide.html Loading and teardown of context Threading model, scheduling, and timers Synchronous file I/O, asynchronous network I/O Synchronization (critsec, mutex, semaphore, events) Debugging and tool support Additional work for port: –JIT (very portable 3 layer macro emitter design) –Small amount of assembly code in execution engine

Build Infrastructure and Utilities Build scripts and programs –Scripts for environment setup and build –build, binplace, nmake, and resource compiler utilities Utility configuration programs –gacutil – manage the “global assembly cache” –sn – manage assembly signing –peverify – verify CIL in an assembly –caspol – modify policy for “code access security” –storeadm – manage “isolated storage”

Build Bootstrap Process Initial phase –Build PAL using native toolchain –Build build tools against PAL –Complete by building resource compiler and PAL runtime using newly compiled build tools Main phase has complex interdependencies –Unmanaged frameworks, compilers, and tools, are built –Managed portions of runtime and frameworks are built –Assemblies and runtime are configured Finally, when managed portions are used at runtime, they are, of course, JIT compiled

Tests Incredibly handy when modifying code! Two major areas: managed code and PAL PAL suites –Test driver script is pvtun.pl –Can be used on new PAL implementations Quality suites –Test driver script is rrun.pl –Three primary areas in this release IL verification “BVT” smoke tests – many small programs Tests for the BCL

Additional Resources ECMA specs: Microsoft commercial C# and CLR SDK Shared source info: