1 Design Of lib/System 2 ==================== 3 4 The software in this directory is designed to completely shield LLVM from any 5 and all operating system specific functionality. It is not intended to be a 6 complete operating system wrapper (such as ACE), but only to provide the 7 functionality necessary to support LLVM. 8 9 The software located here, of necessity, has very specific and stringent design 10 rules. Violation of these rules means that cracks in the shield could form and 11 the primary goal of the library is defeated. By consistently using this library, 12 LLVM becomes more easily ported to new platforms since the only thing requiring 13 porting is this library. 14 15 Complete documentation for the library can be found in the file: 16 llvm/docs/SystemLibrary.html 17 or at this URL: 18 http://llvm.org/docs/SystemLibrary.html 19 20 While we recommend that you read the more detailed documentation, for the 21 impatient, 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 34 To accomplish these requirements, the library has numerous design criteria that 35 must 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
