[llvm-dev] ThinLTO with Linux+ELF+Gold -- incorrectly dropping weak definitions.

David Callahan via llvm-dev
Wed, 17 May 2017 17:42:16 -0000

I have now observed that some of the object files, while compiled -flto=thin and
determined to be missing the ThinLTOSummary and are being lumped into the
"regularLTO" pass. This might explain some of my problem.   Under what
conditions would this summary be missing? Is it ever legal to mix -flto and
-flto=thin object files?

________________________________
From: Teresa Johnson <tejohnson at google.com>
Sent: Tuesday, May 16, 2017 9:52:47 AM
To: David Blaikie
Cc: David Callahan; LLVM Dev Mailing list
Subject: Re: [llvm-dev] ThinLTO with Linux+ELF+Gold -- incorrectly dropping weak
definitions.

This looks similar to the problem I fixed awhile back in r292408. I'll take
a look (probably tomorrow since I am taking some vacation today).
Teresa

On Tue, May 16, 2017 at 9:43 AM, David Blaikie <dblaikie at
gmail.com<mailto:dblaikie at gmail.com>> wrote:
+Teresa

On Mon, May 15, 2017 at 9:20 AM David Callahan via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
I am tracking a problem with ThinLTO on Linux using gold and elf files where
there is a disconnect between gold’s treatment of comdat groups and ThinLTO’s
decisions about which weak references to convert to available externally.  The
net result is a definition is lost and a relocation entry is not handled.

My status is summarized:
https://bugs.llvm.org/show_bug.cgi?id=32980<https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_show-5Fbug.cgi-3Fid-3D32980&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=lFyiPUrFdOHdaobP7i4hoA&m=DPiCkl9b6jP9-AMbNn0dugb9gFBlyNOKzRq3medq--c&s=DrEkmqUOt4bTaMEhOHPJpR7t5uuU7ux0362_rqDXoT4&e=>

Anyone familiar with this space and have guidance? Either on how to avoid the
problem, or a patch to correct it?

Thanks
--david


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--
Teresa Johnson |         Software Engineer |     tejohnson at
google.com<mailto:tejohnson at google.com> |     408-460-2413
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