1Design Of lib/System 2==================== 3 4The software in this directory is designed to completely shield LLVM from any 5and all operating system specific functionality. It is not intended to be a 6complete operating system wrapper (such as ACE), but only to provide the 7functionality necessary to support LLVM. 8 9The software located here, of necessity, has very specific and stringent design 10rules. Violation of these rules means that cracks in the shield could form and 11the primary goal of the library is defeated. By consistently using this library, 12LLVM becomes more easily ported to new platforms since the only thing requiring 13porting is this library. 14 15Complete documentation for the library can be found in the file: 16 llvm/docs/SystemLibrary.html 17or at this URL: 18 http://llvm.org/docs/SystemLibrary.html 19 20While we recommend that you read the more detailed documentation, for the 21impatient, here's a high level summary of the library's requirements. 22 23 1. No system header files are to be exposed through the interface. 24 2. Std C++ and Std C header files are okay to be exposed through the interface. 25 3. No exposed system-specific functions. 26 4. No exposed system-specific data. 27 5. Data in lib/System classes must use only simple C++ intrinsic types. 28 6. Errors are handled by returning "true" and setting an optional std::string 29 7. Library must not throw any exceptions, period. 30 8. Interface functions must not have throw() specifications. 31 9. No duplicate function impementations are permitted within an operating 32 system class. 33 34To accomplish these requirements, the library has numerous design criteria that 35must be satisfied. Here's a high level summary of the library's design criteria: 36 37 1. No unused functionality (only what LLVM needs) 38 2. High-Level Interfaces 39 3. Use Opaque Classes 40 4. Common Implementations 41 5. Multiple Implementations 42 6. Minimize Memory Allocation 43 7. No Virtual Methods 44