- We do some nasty things w.r.t. installing or overriding signal handlers in
order to improve our crash recovery support or interaction with crash
reporting software, and those things are not necessarily appropriate when
LLVM is being linked into a client application that has its own ideas about
how to do things. This gives those clients a way to disable that handling at
build time.
- Currently, the code this guards is all Apple specific, but other platforms
might have the same concerns so I went for a more generic configure
name. Someone who is more familiar with library embedding on Windows can
handle choosing which of the Windows/Signals.inc behaviors might make sense
to go under this flag.
- This also fixes the proper autoconf'ing of ENABLE_BACKTRACES. The code
expects it to be undefined when disabled, but the autoconf check was just
defining it to 0.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189694 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
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