[llvm-dev] LTO, ifuncs, and lld

[Shawn Webb via llvm-dev]

Thanks for providing the patch! I got around to testing it this
morning and it appears it fixes compilation, but produces a
non-working system.

I know that's kinda vague and I'll have more details soon, including
sample binaries. I at least wanted to give a status update so you
didn't think you were being ignored.

Thanks,

-- 
Shawn Webb
Cofounder and Security Engineer
HardenedBSD

Tor-ified Signal:    +1 443-546-8752
Tor+XMPP+OTR:        lattera at is.a.hacker.sx
GPG Key ID:          0x6A84658F52456EEE
GPG Key Fingerprint: 2ABA B6BD EF6A F486 BE89  3D9E 6A84 658F 5245 6EEE

On Wed, Nov 28, 2018 at 09:16:24PM -0800, Peter Collingbourne wrote:
> https://reviews.llvm.org/D55046 fixes your reproducer here. Let me know if
> that works for you.
> 
> Note that I had to rebuild one of your bitcode files to be a regular object
> file, this is because LTO doesn't want the .eh_frame terminator to live in
> a bitcode file.
> 
> $ mv ./usr/lib/crtendS.o ./usr/lib/crtendS.o.bak
> $ ~/l4/ra/bin/llc -o ./usr/lib/crtendS.o ./usr/lib/crtendS.o.bak
> -filetype=obj -relocation-model=pic
> 
> Peter
> 
> On Wed, Nov 28, 2018 at 5:35 PM Shawn Webb <shawn.webb at hardenedbsd.org>
> wrote:
> 
> > Hey Peter,
> >
> > Here you go!
> >
> > https://hardenedbsd.org/~shawn/2018-11-28_reproduce-01.tar
> >
> > Thanks,
> >
> > --
> > Shawn Webb
> > Cofounder and Security Engineer
> > HardenedBSD
> >
> > Tor-ified Signal:    +1 443-546-8752
> > Tor+XMPP+OTR:        lattera at is.a.hacker.sx
> > GPG Key ID:          0x6A84658F52456EEE
> > GPG Key Fingerprint: 2ABA B6BD EF6A F486 BE89  3D9E 6A84 658F 5245 6EEE
> >
> > On Wed, Nov 28, 2018 at 05:30:57PM -0800, Peter Collingbourne wrote:
> > > Hi Shawn,
> > >
> > > Can you please create a reproducer tarball (using ld.lld --reproduce) so
> > > that we don't need to install HardenedBSD in order to reproduce?
> > >
> > > Peter
> > >
> > > On Wed, Nov 28, 2018 at 5:16 PM Shawn Webb via llvm-dev <
> > > llvm-dev at lists.llvm.org> wrote:
> > >
> > > > Hey LLVM folks,
> > > >
> > > > I've run into an interesting assertion. In one of HardenedBSD's
> > > > feature branches, we're working on integration llvm's Cross-DSO CFI
> > > > implementation. Using Cross-DSO CFI requires building libs with LTO,
> > > > which causes clang to emit LLVM IR intermediate object files rather
> > > > than ELF intermediate object files.
> > > >
> > > > I've found that with lld, attempting to link LLVM IR intermediate
> > > > object files hits an assert in lld. I've created a reproduction test
> > > > case in this tiny little repo: https://github.com/lattera/ifunc_repro
> > > >
> > > > The assertion I hit is detailed in the commit message of the initial
> > > > commit:
> > > >
> > > >
> > https://github.com/lattera/ifunc_repro/commit/0be98f9e81a1c91e80b135da6bb8d073d7a0c6f7
> > > >
> > > > HardenedBSD's Cross-DSO CFI feature branch uses clang/llvm/lld 7.0.1.
> > > > I'm more than happy to test out patches to help address this issue.
> > > >
> > > > Please let me know if you have any questions, comments, or concerns.
> > > >
> > > > Thanks,
> > > >
> > > > --
> > > > Shawn Webb
> > > > Cofounder and Security Engineer
> > > > HardenedBSD
> > > >
> > > > Tor-ified Signal:    +1 443-546-8752
> > > > Tor+XMPP+OTR:        lattera at is.a.hacker.sx
> > > > GPG Key ID:          0x6A84658F52456EEE
> > > > GPG Key Fingerprint: 2ABA B6BD EF6A F486 BE89  3D9E 6A84 658F 5245 6EEE
> > > > _______________________________________________
> > > > LLVM Developers mailing list
> > > > llvm-dev at lists.llvm.org
> > > > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> > > >
> > >
> > >
> > > --
> > > --
> > > Peter
> >
> 
> 
> -- 
> -- 
> Peter
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