[Pkg-d-devel] Bug#857085: terminix FTBFS on armhf: Error executing /usr/bin/ldc2: Segmentation fault

[Iain Buclaw]

On 24 April 2017 at 20:04, Matthias Klumpp <matthias at tenstral.net> wrote:
> Hi!
>
> Here is a short summary on the bug:
>
> 1) It only happens on Debian buildds, Fedora and Arch are not
> affected. I examined the build logs and the environments are
> relatively similar, with a notable difference for Fedora being that
> they build with GCC 7
>
> 2) The issue itself is an infinite loop in
> `TemplateInstance::needsCodegen` which shouldn't be possible, and
> upstream has no idea why it happens. Debugging the issue is really
> hard.
>
> 3) Suddenly we started to get the same bug reproducibly on i386
> buildds as well for LDC itself, see[1]. There, the bug is in the
> bootstrap process, which uses an older compiler that worked fine
> already for many Debian releases. This suggests that the actual issue
> might be in a different portion of the code, or something else has
> changed that is now triggering the issue.
>
> 4) Compiling LDC in a i386 chroot on an arm64 host always works
> without any issues - the problem appears only on the buildd (which
> itself is an amd64 host...).
>
> 5) The same applied to the crash on armhf which never happens when
> cross-compiling, but only on a real armhf machine.
>
> 6) The problem is not LDC being miscompiled during bootstrap, nor does
> compiling with LLVM 3.8 instead of 3.9 change anything.
>
> 7) The crash disappears when running in GDB (or valgrind)
>
> I am really out of ideas on this - upstream suggested some valgrinding
> and gdb-ing, but doing that is very cumbersome as the only place where
> I can reproduce this bug that isn't a Debian buildd is an armhf
> porterbox (and armhf is really slow...), and as soon as you run the
> application in gdb the crash vanishes.
>
> Creating a minimized testcase would take multiple weeks on armhf, and
> ultimately failed a few weeks back - but we uncovered another bug in
> the process, which was resolved meanwhile, so at least something good
> came out of it.
>
> Any help would be highly appreciated!
> Cheers,
>     Matthias Klumpp
>
> [1]: https://buildd.debian.org/status/fetch.php?pkg=ldc&arch=i386&ver=1%3A1.1.1-3&stamp=1493055455&raw=0
>

If running in gdb makes the problem go away, have you tried turning on
core dumps in buildd?

--
Iain.