[llvm-dev] (Thin)LTO llvm build

[Teresa Johnson via llvm-dev]

On Tue, Dec 20, 2016 at 11:05 AM, Carsten Mattner <carstenmattner at gmail.com>
wrote:

> On Tue, Dec 20, 2016 at 5:05 PM, Teresa Johnson <tejohnson at google.com>
> wrote:
> > Hi Carsten,
> >
> > A few responses below, but first, can you get the link command for
> > lldb.so.3.9.1? Last time it was the lldb.so build that was using
> > ld.bfd with the gold plugin which was exposing this issue.
>
> Where would I find it in an otherwise already terminated process?
>

I think you can get this via "ninja -t commands bin/lldb-argdumper" (this
will give you a lot of output, all of the compilation commands used to
build that target). Or redo the build with -v to be sure.

Teresa


> > On Tue, Dec 20, 2016 at 5:49 AM, Carsten Mattner <
> carstenmattner at gmail.com>
>
> > No problem - I assumed no news was good news! Thanks for the
> > explicit feedback though!
>
> Sure, but it's important, and I've had my experience with never
> hearing back even after asking for confirmation of success. Same as
> drive-by patch drops.
>
> > > - Should I avoid any and all CFLAGS, CXXFLAGS, CPPFLAGS, LDFLAGS
> > >   in favor of passing these exclusively as cmake's
> > >   -Dsomething_something=<FLAGS>? Linux distros usually have an
> > >   environment with CFLAGS etc. and use that building packages and
> > >   this didn't interfere in the past in my builds, but I'm open to
> > >   avoid this by unsetting any such variables first.
> >
> >
> > The problem I've had in the past setting *FLAGS on the cmake command
> > line is that sometimes the configure fails because it uses those
> > flags in various configuration checking compiles. So typically I
> > hand edit the resulting CMakeCache.txt if I want to pass specific
> > options to the build. Note that there are various flavors of e.g.
> > LINKER_FLAGS that get passed to different types of links though
> > (SHARED vs EXE etc). I haven't tried setting CFLAGS etc env
> > variables before kicking off the ninja build to pass args.
>
> I set the variables before running cmake and I didn't expect for it to
> be re-considered when running ninja, but it would of course more
> closely mirror make's behavior if it does/dit.
>
> > > - Is there a configuration in the CI matrix that builds all
> > >   of LLVM with ThinLTO so that I can be reasonably sure
> > >   any error is most likely local to my environment or
> > >   because of operator (silly me) faults?
> >
> >
> > There is an lld based ThinLTO buildbot. I've been really remiss in
> > not setting up a gold based ThinLTO bot...note to self to get that
> > done asap! But the existing lld will be head not 3.9.
>
> Please have it build everything that's buildable in the llvm tree.
>
> > > I also pass these in LDFLAGS but they're not visible
> > > in the error trace below:
> > >     -Wl,-plugin-opt,-function-sections \
> > >     -Wl,-plugin-opt,-data-sections \
> >
> >
> > Hmm, looks like LDFLAGS doesn't work for passing to the resulting link
> line?
> > Try setting in the CMakeCache.txt as described above.
>
> It's a mystery (aka haven't traced/debugged CMake).
>
> > > Any idea why lldb-argdumper would fail to link reproducably?
> >
> > See suggestion above about looking at lldb.so.3.9.1 link line. Let's
> > make sure that looks ok first.
>
> Thanks.
>



-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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