[llvm-dev] archiving LTO objects broken for current Xcode releases

[Mehdi Amini via llvm-dev]

> On Oct 26, 2016, at 8:06 AM, Jack Howarth via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
>    The ability to archive object files generated with -flto under
> LLVM.org clang 3.9.0 or 4.0svn trunk is broken against the currently
> shipping Xcode releases including the upcoming Xcode 8.1 GM.
> 
> https://llvm.org/bugs/show_bug.cgi?id=30791
> 
> $ clang-3.9 -flto -O1 -c *.i
> $ ar cr libtar.a paxerror.o paxexit-status.o paxnames.o rtapelib.o
> stdopen.o wordsplit.o xattr-at.o
> error: Unknown attribute kind (52) (Producer: 'LLVM3.9.0' Reader:
> 'LLVM APPLE_1_800.0.42.1_0')
> /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar:
> internal ranlib command failed
> 
> Using MacPorts, I've been able to confirm that archiving LTO object
> files now requires a cctools release that has been built against llvm
> 3.9.0 rather than 3.8.1 to avoid this failure.
>     Was this change intentional and is there any possibility of
> restoring compatibility with the currently shipping Xcode releases?

This is not a bug, and not a goal to solve this: “older” LLVM versions can’t read newer bitcode.

You need either to:

1) use llvm-ar that ships with 3.9/4.0, 
2) export a DYLD_LIBRARY_PATH that points to the path where the 3.9/4.0 libLTO.dylib is. The Xcode ar will load libLTO.dylib.

If none of this fits your need, please be more specific on the use case so that we can come up with a better solution.

Best,

— 
Mehdi