Shared Source CLI Essentials

Bootstrapping the Assembly Load Process

Executing the code stored within an assembly is a chicken-and-egg scenario. The assembly cannot execute until it has been resolved, loaded into the CLI, verified, and JIT-compiled. The CLI itself is simply a body of code, contained in assemblies that must be loaded into the process space and run. Fortunately, this is a classic bootstrapping problem, and implementation solutions abound. For the SSCLI implementation, a special entry point into the primary assembly is all that is needed, along with some initial security conditions, which are attached to the assembly as data.

The bootstrap API makes hosting the CLI a simple thing to do, as evinced by Rotor’s program launcher, clix.exe, whose code can be found in sscli/clr/src/tools/clix, and whose main function, Launch, appears without error handling in Example 4-5.

Example 4-5. The Launch function of clix.exe

DWORD Launch(WCHAR* pRunTime, WCHAR* pFileName, WCHAR* pCmdLine) { HANDLE hFile = NULL; HANDLE hMapFile = NULL; PVOID pModule = NULL; HINSTANCE hRuntime = NULL; DWORD nExitCode = 1; DWORD dwSize; DWORD dwSizeHigh; IMAGE_DOS_HEADER* pdosHeader; IMAGE_NT_HEADERS32* pNtHeaders; IMAGE_SECTION_HEADER* pSectionHeader; WCHAR exeFileName[MAX_PATH + 1]; // open the file & map it hFile = ::CreateFile(pFileName, GENERIC_READ, FILE_SHARE_READ, 0, OPEN_EXISTING, 0, 0); hMapFile = ::CreateFileMapping(hFile, NULL, PAGE_WRITECOPY, 0, 0, NULL); pModule = ::MapViewOfFile(hMapFile, FILE_MAP_COPY, 0, 0, 0); ...