GHC status report
Carter Schonwald
carter.schonwald at gmail.com
Sat May 3 01:12:00 UTC 2014
if theres a way i can patch llvm-general so that i can use it with llvm
static linked into rather than dylinked, i'm all ears!
llvm-general has to use some C++ wrappers (that in turn use extern "C"
sections) to make parts of the llvm api accessible from hasskell.
I had trouble following some of the thread earlier today, but is the
suggestion to try building those wrappers with -fPIC would make them play
nice?
On Fri, May 2, 2014 at 8:52 PM, Dominick Samperi <djsamperi at gmail.com>wrote:
> I posted a ticket related to this (#8371), but the example provided there
> has no problems today for all versions of ghci that I tested (including
> 7.6.3), provided -fno-ghci-sandbox is specified. So this problem was
> clearly related to the threads issue.
>
> Today there are problems when DYNAMIC_GHC_PROGRAMS=NO, but they
> happen later, and I have not yet narrowed this down to a small example.
> Basically, I have an Haskell app that embeds R (as in the sample code
> attached to the above ticket), but when it tries to do some calculations
> it seg faults (works fine with 7.8.2).
>
> On Fri, May 2, 2014 at 3:45 PM, Simon Marlow <marlowsd at gmail.com> wrote:
> > Can you give me a quick summary of how to reproduce the problem? (not
> > including the GHC build steps)
> >
> > Cheers,
> > Simon
> >
> >
> > On 02/05/14 18:18, Dominick Samperi wrote:
> >>
> >> I downloaded HEAD and placed DYNAMIC_GHC_PROGRAMS=NO in the "quick"
> >> section of mk/build.mk (with BuildFlavour = quick), and set
> >> DYNAMIC_GHC_PROGRAMS=NO
> >> in my environment before running configure (just to be sure!). Near
> >> the end of the build
> >> I saw some messages like "Warning: vectorization failure," but the
> >> build completed.
> >>
> >> The status at the end of configure doesn't say that dynamic linking
> >> via RTS has been
> >> turned off, and I don't know how to check that this is so.
> >> Nevertheless, I checked
> >> the linking issue and it is NOT fixed with this build, so
> >> DYNAMIC_GHC_PROGRAMS=YES is required to prevent the problems
> >> reported by me and others.
> >>
> >>
> >> On Fri, May 2, 2014 at 9:09 AM, Simon Marlow <marlowsd at gmail.com>
> wrote:
> >>>
> >>> On 02/05/2014 01:09, Dominick Samperi wrote:
> >>>
> >>>> If I understand your last comment correctly linking to libR should
> >>>> continue to work, even if you revert to static linking of Haskell
> >>>> compiled
> >>>> code via RTS linker. Since you say this is the way things have always
> >>>> been, perhaps the real explanation for why 7.8 fixed the issue is that
> >>>> some bug was fixed along the way...
> >>>
> >>>
> >>>
> >>> Indeed. To know for sure we would have to test 7.8 with
> >>> DYNAMIC_GHC_PROGRAMS=NO with your setup - is there a way to do that?
> >>>
> >>> Cheers,
> >>> Simon
> >>>
> >>>
> >>>
> >>>> Note that R is a C library, so the C++ issues that Carter mentions are
> >>>> not a factor here.
> >>>>
> >>>> Thanks,
> >>>> Dominick
> >>>>
> >>>> On Thu, May 1, 2014 at 5:27 PM, Simon Marlow <marlowsd at gmail.com>
> wrote:
> >>>>>
> >>>>>
> >>>>> On 01/05/14 14:48, Dominick Samperi wrote:
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> The problem with some graphics libraries used via FFI (and other
> >>>>>> libraries
> >>>>>> that are not thread-safe), if I understand the situation correctly,
> is
> >>>>>> that ghci
> >>>>>> forks a thread when it shouldn't, causing some programs to
> >>>>>> miscalculate
> >>>>>> the available stack space (because they think there is only one
> >>>>>> thread).
> >>>>>
> >>>>>
> >>>>>
> >>>>>>
> >>>>>>
> >>>>>> The new dynamic linking support and the flag -fno-ghci-sandbox fixes
> >>>>>> this problem, and I would not vote for the removal of these
> features.
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>> So I understand how -fno-ghci-sandbox avoids problems with GUI
> >>>>> libraries
> >>>>> that use thread-local state. But how is dynamic linking involved
> here?
> >>>>> What improved in GHC 7.8 relative to 7.6 for you? And could you
> clarify
> >>>>> "miscalculate the available stack space"? What needs to calculate
> stack
> >>>>> space? Why? C stack space?
> >>>>>
> >>>>> We can certainly make a smoother experience around -fno-ghci-sandbox
> >>>>> for
> >>>>> using GUI libraries.
> >>>>>
> >>>>>
> >>>>>> It is not clear to me from Simon's original post how linking to all
> of
> >>>>>> those C++ libs can continue to work if dynamic linking is removed
> >>>>>> in 7.10? Perhaps I misunderstand what you mean by "revert to
> >>>>>> static linking"?
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>> When I say "revert to static linking" I mean make GHCi static linked,
> >>>>> and
> >>>>> have it load Haskell code compiled for static linking using the RTS
> >>>>> linker
> >>>>> (like it did in 7.6). Foreign libraries would still be loaded using
> >>>>> the
> >>>>> system linker, as they always have been.
> >>>>>
> >>>>> To be clear, I'm not officially proposing that we drop dynamic
> linking,
> >>>>> but
> >>>>> I think it's worthwhile exploring the design space again, given that
> we
> >>>>> know
> >>>>> dynamic linking has been tougher than we expected.
> >>>>>
> >>>>> Cheers,
> >>>>> Simon
> >>>>>
> >>>>>
> >>>>>
> >>>>>> Thanks,
> >>>>>> Dominick
> >>>>>>
> >>>>>>
> >>>>>> On Wed, Apr 30, 2014 at 9:26 PM, George Colpitts
> >>>>>> <george.colpitts at gmail.com> wrote:
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> To elaborate, in the past, I had a lot of problems using libraries
> >>>>>>> from
> >>>>>>> the
> >>>>>>> ghci prompt on the Mac but I haven't tried recently.
> >>>>>>>
> >>>>>>> As an example, on the web page for the book the Haskell School of
> >>>>>>> Expression
> >>>>>>> it says:
> >>>>>>>
> >>>>>>> Note for OS X users: running graphics applications from GHCi is no
> >>>>>>> longer
> >>>>>>> supported. Instead, one has to compile a graphics program using GHC
> >>>>>>> in
> >>>>>>> order
> >>>>>>> to run it (see example/GMIExamples.lhs for an example).
> >>>>>>>
> >>>>>>> I had similar problems using the Yale Euterpea music program from
> >>>>>>> ghci.
> >>>>>>> When
> >>>>>>> I inquired I was referred to
> >>>>>>> https://ghc.haskell.org/trac/ghc/ticket/4244
> >>>>>>> and https://ghc.haskell.org/trac/ghc/ticket/781. I see that the
> >>>>>>> latter
> >>>>>>> is
> >>>>>>> now scheduled for 7.10.1
> >>>>>>>
> >>>>>>>
> >>>>>>> On Wed, Apr 30, 2014 at 1:45 PM, Simon Marlow <marlowsd at gmail.com>
> >>>>>>> wrote:
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> On 30/04/2014 01:35, George Colpitts wrote:
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> It doesn't have anything about the dynamic linking changes made
> for
> >>>>>>>>> 7.8.
> >>>>>>>>> I think it's worth mentioning the improvements we expect to get
> >>>>>>>>> from
> >>>>>>>>> that. The highlights of the release notes do mention it, so maybe
> >>>>>>>>> that
> >>>>>>>>> suffices.
> >>>>>>>>>
> >>>>>>>>> In particular, I'm hoping that it is going to fix a lot of
> problems
> >>>>>>>>> with
> >>>>>>>>> using foreign libraries such as OpenGL from ghci. I could be
> wrong
> >>>>>>>>> about
> >>>>>>>>> that though.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> I'd like to understand more about what those problems are. As a
> >>>>>>>> data
> >>>>>>>> point, at Facebook we're using static linking (I compiled GHC with
> >>>>>>>> DYNAMIC_GHC_PROGRAMS=NO), we're loading upwards of 50 3rd-party
> C++
> >>>>>>>> libraries and one gigantic shared library consisting of a ton of
> >>>>>>>> in-house
> >>>>>>>> C++ code, together with all our Haskell code into GHCi, and it
> works
> >>>>>>>> perfectly. The key to using the static linker is to not use it
> for
> >>>>>>>> C++
> >>>>>>>> code
> >>>>>>>> - you want all your external C++ code in shared libraries and load
> >>>>>>>> those
> >>>>>>>> using the system linker.
> >>>>>>>>
> >>>>>>>> Dynamic linking has been a huge headache in GHC, and it's not
> clear
> >>>>>>>> that
> >>>>>>>> it's an overall improvement compared with the static linker. Now
> >>>>>>>> that
> >>>>>>>> 7.8
> >>>>>>>> is out of the way, it's time to have a conversation about whether
> we
> >>>>>>>> want to
> >>>>>>>> do dynamic linking again for 7.10, or revert to static linking. I
> >>>>>>>> think
> >>>>>>>> Austin is going to update
> >>>>>>>> https://ghc.haskell.org/trac/ghc/wiki/DynamicGhcPrograms, and
> then
> >>>>>>>> we'll
> >>>>>>>> see
> >>>>>>>> where we stand.
> >>>>>>>>
> >>>>>>>> Cheers,
> >>>>>>>> Simon
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>>
> >>>>>>>>> On Tue, Apr 29, 2014 at 6:13 PM, Simon Peyton Jones
> >>>>>>>>> <simonpj at microsoft.com <mailto:simonpj at microsoft.com>> wrote:
> >>>>>>>>>
> >>>>>>>>> As Austin has told us, there's a draft of the *GHC Status
> >>>>>>>>> Report
> >>>>>>>>> for
> >>>>>>>>> the HCAR*, here:____
> >>>>>>>>>
> >>>>>>>>> https://ghc.haskell.org/trac/ghc/wiki/Status/May14____
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Have we missed out something you have been working hard
> on?
> >>>>>>>>> Do
> >>>>>>>>> take a moment to add a bullet in an appropriate place
> (it's
> >>>>>>>>> a
> >>>>>>>>> wiki). I'd like to be sure that we are giving credit to
> all
> >>>>>>>>> the
> >>>>>>>>> appropriate people, so please help us fix that too. GHC
> is
> >>>>>>>>> a
> >>>>>>>>> team
> >>>>>>>>> effort.____
> >>>>>>>>>
> >>>>>>>>> Deadline is 1 May I think.____
> >>>>>>>>>
> >>>>>>>>> Thanks____
> >>>>>>>>>
> >>>>>>>>> Simon____
> >>>>>>>>>
> >>>>>>>>> __ __
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> _______________________________________________
> >>>>>>>>> ghc-devs mailing list
> >>>>>>>>> ghc-devs at haskell.org <mailto:ghc-devs at haskell.org>
> >>>>>>>>> http://www.haskell.org/mailman/listinfo/ghc-devs
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> _______________________________________________
> >>>>>>>>> ghc-devs mailing list
> >>>>>>>>> ghc-devs at haskell.org
> >>>>>>>>> http://www.haskell.org/mailman/listinfo/ghc-devs
> >>>>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> _______________________________________________
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> >>>>>>>
> >>>>>
> >>>
> >
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