[PATCH] D22677: [ThinLTO/gold] Support for getting list of included objects from gold

[Xinliang David Li via llvm-commits]

Can we have a subdir in the test that requires latest version of gold -- so
that more tests can be added?

David

On Fri, Jul 22, 2016 at 11:41 AM, Teresa Johnson <tejohnson at google.com>
wrote:

> tejohnson added inline comments.
>
> ================
> Comment at: test/tools/gold/X86/thinlto_emit_linked_objects.ll:18
> @@ +17,3 @@
> +; RUN:    %t.o \
> +; RUN:    --start-lib %t2.o --end-lib
> +
> ----------------
> tejohnson wrote:
> > mehdi_amini wrote:
> > > tejohnson wrote:
> > > > tejohnson wrote:
> > > > > tejohnson wrote:
> > > > > > mehdi_amini wrote:
> > > > > > > tejohnson wrote:
> > > > > > > > tejohnson wrote:
> > > > > > > > > davidxl wrote:
> > > > > > > > > > tejohnson wrote:
> > > > > > > > > > > davidxl wrote:
> > > > > > > > > > > > tejohnson wrote:
> > > > > > > > > > > > > davidxl wrote:
> > > > > > > > > > > > > > Perhaps add test case about real archive case as
> well.
> > > > > > > > > > > > > For a distributed build the build system needs to
> extract the constituent objects (otherwise the combined index paths will
> not point to an object file)
> > > > > > > > > > > > I think this feature is more about two step link
> (not about a particular distributed build system). It is possible that some
> other distributed build system uses archive, right?
> > > > > > > > > > > Using archives directly with a distributed build won't
> work - the combined index module paths need to point to an object file for
> the distributed backends to import from. The build system needs to extract
> the objects (e.g. into a temp dir) and pass those.
> > > > > > > > > > >
> > > > > > > > > > > Note that archives passed to a non-distributed build
> work fine because we load the modules from the offset within the archive
> passed to the plugin from gold and serve those to the importer.
> > > > > > > > > > how about thin archive?
> > > > > > > > > Gold does not seem to like thin archives (regardless of
> LTO vs ThinLTO). I get an error (from gold, not the plugin) like:
> > > > > > > > >
> > > > > > > > > error: foo.a: no archive symbol table (run ranlib)
> > > > > > > > >
> > > > > > > > > (even when I run ranlib)
> > > > > > > > Note this issue is specific to bitcode files in the archive
> - gold with regular native objects in a thin archive works just fine. Looks
> like ranlib doesn't work on an archive of bitcode files, and that seems to
> be needed with a thin archive.
> > > > > > > Do you mean "ranlib doesn't work on a *thin* archive of
> bitcode files"?
> > > > > > > Otherwise how do you build LLVM itself with LTO?
> > > > > > According to http://llvm.org/docs/GoldPlugin.html it isn't
> supported for archives of bitcode files at all, but apparently isn't needed
> for a whole (non-thin) archive:
> > > > > >
> > > > > > "export RANLIB=/bin/true #ranlib is not needed, and doesn't
> support .bc files in .a"
> > > > > So I can't get gold to work with a (non-thin) archive created by
> ar, it gives the same error. Maybe it needs to take the -plugin option? In
> any case, a non-thin archive created via llvm-ar is accepted and works
> fine. I don't see an llvm-ar option to create a thin archive though?
> > > > Aha - llvm-ar does support thin archives, it's just that the T
> option is not documented in the help. =)
> > > >
> > > > With that, it does work for llvm-ar thin archives! Will add another
> case to the new test that does the same for thin archives before submitting.
> > > > According to http://llvm.org/docs/GoldPlugin.html it isn't
> supported for archives of bitcode files at all.
> > >
> > > Documentation patch?
> > Reading through that page some more, it gives instructions earlier on
> getting the plugin to work with ar:
> > "ar and nm also accept the -plugin option and it’s possible to to
> install LLVMgold.so to /usr/lib/bfd-plugins for a seamless setup. If you
> built your own gold, be sure to install the ar and nm-new you built to
> /usr/bin."
> >
> > So I think it is ok. I just took the latter comment out of context.
> >
> > However, I will send a patch to document the llvm-ar T modifier
> > With that, it does work for llvm-ar thin archives! Will add another case
> to the new test that does the same for thin archives before submitting.
>
> And, removed in r276453 due to bot failure - looks like gold v1.11 does
> not like the thin archive (gold v1.12 is fine though!).
>
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D22677
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160722/5d59df8c/attachment.html>