[cfe-dev] [LLVMdev] New libc++ LLVM Subproject

[Christopher Jefferson]

On 13 May 2010, at 17:57, Ahmed Charles wrote:

>>> That is not set in stone at this point.
>> 
>> Ah, I'm very glad to hear it!
>> 
>>> An "abi-versioned" debug mode is another possibility.
>> 
>> Sounds intriguing. :)
>> 
> 
> VC2010 has pragma detect_mismatch for issues like this:
> http://msdn.microsoft.com/en-us/library/ee956429.aspx I'm sure it wouldn't
> be too hard to implement, if the entire toolchain is LLVM.
> 
> I'm also curious as to why major versions of libstdc++ and libc++ (in the
> future) would require ABI compatibility? Considering that MS breaks ABI
> compatibility with each version, is there anything about the users of other
> toolchains that make ABI compatibility a greater concern? My impression of
> FOSS has always been that compatibility is an easier issue because the
> source for most things is always available. Perhaps having a consistent ABI
> versioning story for libc++ is something that should be looked into?

Consider someone who has boost ( a large C++ library) installed on their linux / mac box.

The standard library which boost was compiled against must be ABI compatible with the version used in every application using boost. Updates require either supporting multiple ABI-incompatible versions of the boost library and headers at the same time, or having a single "break the world", where every application is recompiled at the same time. I've had to do that before and it is very painful.

Windows has tried harder to make this kind of thing work in the past, linux and mac less so.

A fundamentally different approach to libraries, other than just dumping the boost headers in /usr/local/include/boost and the library in /usr/local/lib would be required to make this work.

Chris