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

[Jack Howarth via llvm-dev]

On Wed, Oct 26, 2016 at 11:12 AM, Mehdi Amini <mehdi.amini at apple.com> wrote:
>
>> 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.
>

Thanks. Actually both llvm-ar and llvm-ranlib have to be used for
builds with -flto that create library archives to work.
       Jack

> Best,
>
> —
> Mehdi
>