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That causes references to them to be weak references which can collapse to null if no definition is provided. We call these functions unconditionally, so a definition *must* be provided. Make the definitions provided in the .cpp file weak by re-declaring them as weak just prior to defining them. This should keep compilers which cannot attach the weak attribute to the definition happy while actually resolving the symbols correctly during the link. You might ask yourself upon reading this commit log: how did *any* of this work before? Well, fun story. It turns out we have some code in Support (BumpPtrAllocator) which both uses virtual dispatch and has out-of-line vtables used by that virtual dispatch. If you move the virtual dispatch into its header in *just* the right way, the optimizer gets to devirtualize, and remove all references to the vtable. Then the sad part: the references to this one vtable were the only strong symbol uses in the support library for llvm-tblgen AFAICT. At least, after doing something just like this, these symbols stopped getting their weak definition and random calls to them would segfault instead. Yay software. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205137 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