On 08/02/17 13:11 +0100, Marek Skalický wrote:
Marek Polacek píše v Út 07. 02. 2017 v 22:32 +0100:
It's been a tradition now that every January we rebuild all the
Fedora packages
with the upcoming GCC, to reveal as many bugs as possible before we
release
the new version. This year is no different.
There were 18811 packages overall (last year we had 17741 packages).
17263 built fine with the new GCC (mostly gcc-7.0.0-0.1.fc26.src.rpm
but I also
used a newer version from rawhide). 1350 failed with both GCC 6 and
GCC 7,
so I ignored these. This left us with ~198 packages that had to be
analyzed,
a number which, fortunately, was smaller than last year, when we'd
had 577 FTBFS to
investigate.
MongoDB is not failing in your rebuild. However latest minor upgrade
(v3.4.2) with gcc 7 is failing.
I've figured out, that is optimization issue (with -O0 it is fine, with
-01 it is failing) and it is ONLY ON ppc64le (other architectures are
fine).
I know which file is cause this issue, but I can't figure out with
which optimization. I get what changes between O0 and O1 in output of
'gcc -O0/1 -Q --help=optimizers' and compiled with -O0 and flags of
individual optimizations (which are added by O1), but failure does not
appear.
Because that doesn't work, see
https://gcc.gnu.org/wiki/FAQ#optimization-options
If you use -O0 then there is ***no*** optimization. At all. None. The
optimizers aren't used, so it doesn't matter which optimizers you
enable with -fxxx flags, none of them gets used.
If you want to narrow down which flag causes the problem you need to
enable optimization (so at least -O1 or -Os or -Og) and then disable
individual optimizations.
i.e. instead of starting with -O0 and adding -faaa and -fbbb, start
with -O1 and use -fno-aaa and -fno-bbb.
What else differs in -O1? How should I debug it?
https://gcc.gnu.org/wiki/FAQ#misoptimization
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