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043cc54d6c
The LLVMSupport library implementation consolidates all dependencies on system libraries. Move the logic gathering system libraries out of 'cmake/modules/LLVM-Config.cmake' and into 'lib/Support/CMakeLists.txt'. Use the target_link_libraries() command there to tell CMake about the link dependencies of the LLVMSupport implementation. CMake will automatically propagate this to all targets that link LLVMSupport directly or indirectly. We still need to build knowledge of system library dependencies into 'llvm-config'. Store the list of libraries needed in a property on LLVMSupport and teach 'tools/llvm-config/CMakeLists.txt' to retrieve it from there. Drop all calls to 'link_system_libs' and 'get_system_libs' from our CMake code. Replace their implementations with a warning that explains the calls are no longer necessary. Also drop from 'LLVMConfig.cmake' the HAVE_* and related variables that were published there only to allow 'get_system_libs' to run outside our build process. Contributed by Brad King. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201969 91177308-0d34-0410-b5e6-96231b3b80d8
Design Of lib/System
====================
The software in this directory is designed to completely shield LLVM from any
and all operating system specific functionality. It is not intended to be a
complete operating system wrapper (such as ACE), but only to provide the
functionality necessary to support LLVM.
The software located here, of necessity, has very specific and stringent design
rules. Violation of these rules means that cracks in the shield could form and
the primary goal of the library is defeated. By consistently using this library,
LLVM becomes more easily ported to new platforms since the only thing requiring
porting is this library.
Complete documentation for the library can be found in the file:
llvm/docs/SystemLibrary.html
or at this URL:
http://llvm.org/docs/SystemLibrary.html
While we recommend that you read the more detailed documentation, for the
impatient, here's a high level summary of the library's requirements.
1. No system header files are to be exposed through the interface.
2. Std C++ and Std C header files are okay to be exposed through the interface.
3. No exposed system-specific functions.
4. No exposed system-specific data.
5. Data in lib/System classes must use only simple C++ intrinsic types.
6. Errors are handled by returning "true" and setting an optional std::string
7. Library must not throw any exceptions, period.
8. Interface functions must not have throw() specifications.
9. No duplicate function impementations are permitted within an operating
system class.
To accomplish these requirements, the library has numerous design criteria that
must be satisfied. Here's a high level summary of the library's design criteria:
1. No unused functionality (only what LLVM needs)
2. High-Level Interfaces
3. Use Opaque Classes
4. Common Implementations
5. Multiple Implementations
6. Minimize Memory Allocation
7. No Virtual Methods