Bug#1023649: ghc: FTBFS haskell-random powerpc (ghc Segmentation fault)

[John Paul Adrian Glaubitz]

Hi Ilias!

On Wed, 2023-09-20 at 14:54 +0300, Ilias Tsitsimpis wrote:
> Thanks for working on this, comments inline.

Thanks for the useful hints!

> On Wed, Sep 20, 2023 at 12:15PM, John Paul Adrian Glaubitz wrote:
> > I have been bisecting this issue but in order to be successful, I need a simple
> > reproducer which isn't trivial since I cannot just reuse the build directory of
> > an unsuccessful build due to the changing Haskell libraries for different GHC
> > versions.
> > 
> > Ideally, we should have a single command line with GHC which will trigger the
> > segmentation fault.
> 
> Are you bisecting the segfault issue? If yes, then a simple reproducer
> would be to try and compile haskell-random.
> 
> Since you already have cabal-install on your system, you can do
> something like:
> 
>   $ cabal install --with-ghc=/usr/bin/ghc --with-ghc-pkg=/usr/bin/ghc-pkg random-1.2.1.1
> 
> (replace ghc and ghc-pkg with the ones you have built).

Thanks, this is the exact reproducer I need. I can reproduce the crash using this
command line inside a 32-bit PowerPC chroot on perotto with ghc 9.0.2.

> > To bisect, I have done the following:
> > 
> > # git bisect start
> > # git bisect good ghc-8.10.7-release
> > # git bisect bad ghc-9.2.7-release
> 
> Since this issue is also present in ghc-9.0.2, maybe we can start from
> there.

Yes, that's what I am trying now as well.

> > # git submodule update --init
> > # ./boot ; python3 boot
> > # echo "SRC_HC_OPTS += -lffi -latomic -optl-pthread" >> mk/build.mk && \
> >   echo "Stage1Only := YES" >> mk/build.mk && \
> >   echo 'utils/genprimopcode_CONFIGURE_OPTS += "-f-build-tool-depends"' \
> >   >> mk/build.mk && echo 'compiler_CONFIGURE_OPTS += "-f-build-tool-depends"' \
> >   >> mk/build.mk && echo 'utils/hpc_CONFIGURE_OPTS += "-f-build-tool-depends"' \
> >   >> mk/build.mk && echo "HADDOCK_DOCS := NO" >> mk/build.mk \
> >   && echo "BUILD_SPHINX_HTML := NO" >> mk/build.mk && echo "BUILD_SPHINX_PDF := NO" \
> >   >> mk/build.mk
> > # ./configure && make -j32
> > 
> > For newer versions, the build has to be performed with Hadrian, so the last step
> > would be:
> > 
> > # ./hadrian/build -j
> 
> Keep in mind that hadrian doesn't take into account 'mk/build.mk'. You
> will have to configure hadrian in the same way, see also
> https://www.haskell.org/ghc/blog/20220805-make-to-hadrian.html.

Thanks, good to know!

> Let me summarize the current state to make sure we are not missing
> anything:
> 
> 1. GHC 9.0.2 with the native code generator is currently broken on
> powerpc and segfaults while building (at least) haskell-random and
> GHC-9.4.6. Strangely enough, we can compile GHC 9.0.2 itself.
> 
> 2. An unregisterised GHC 9.0.2 is *also* broken on powerpc, producing 
> code that overflows integers. We are also seeing unregisterised GHC
> 9.4.6 on i386 being broken, since the tests for haskell-quickcheck fail
> (see https://buildd.debian.org/status/package.php?p=haskell-quickcheck&suite=sid).
> The plan for i386 is to registerise GHC and use the LLVM backend by
> default (to avoid the baseline violation).

I see.

> 3. We cannot cross-compile GHC 9.4 and newer any more (we are discussing
> this here as well https://gitlab.haskell.org/ghc/ghc/-/issues/23975).

This can be trivially fixed with the help of this patch:

> https://gitlab.haskell.org/ghc/ghc/-/commit/9cb385098f2dfd647c13ca509d71786c56277cff

> Given the above, I can think of the following:
> 
> 1. Fix the native code generator in GHC 9.0.2
> 2. Fix unregisterised GHCs on 32-bit architectures

FWIW, I am seeing the overflow on 32-bit PowerPC only. I don't see it on m68k, for example.

> 3. Try and use the LLVM backend in GHC 9.0.2 on powerpc, and see if this
> produces valid code and allows us to compile GHC 9.4.6.

Ah, that's actually a possible approach to take.

FWIW, I have not been able to build GHC from git on 32-bit PowerPC even for 8.10.7. I assume,
I will need to add some of Debian's patches on top of vanilla GHC in order to get the build
to succeed.

Trying to build GHC 9.0.2 fails for example with:

> http://paste.debian.net/hidden/31954e9a/

> For the record, I have started working on migrating GHC in Debian to use
> the new Hadrian build system, you can find the latest code here
> https://salsa.debian.org/haskell-team/DHG_packages/-/tree/hadrian. I am
> at a really good state right now where I can build GHC, and doing a lot
> of tests to verify I haven't missed anything. If you are working on GHC
> right now as well, I would appreciate if you can take a look, and/or
> start using this branch for all your tests, so we catch any errors
> early.

I want to get the build issue on 32-bit PowerPC sorted out first.

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
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