[lfs-dev] gcc test failures with current svn

Romain Geissler romain.geissler at amadeus.com
Sun Aug 7 11:47:32 PDT 2016


Hi,

On Sun, 7 Aug 2016, Ken Moffat wrote:

> On Sun, Aug 07, 2016 at 12:20:23PM -0500, Bruce Dubbs wrote:
> > Ken Moffat wrote:
> >
> > Isn't -flto the gold linker?  I'm not sure.
> >
> > Didn't someone once say that if you don't follow the book and something
> > breaks, that you get to keep the pieces?
> >
> > [snip]
>
> Probably (-flto), certainly the book doesn't enable the plugins.
> And yes, I'm keeping all the pieces.

The book neither explicitly disable the linker plugin. So as we are
using up to date binutils which supports the linker plugin, on a non
exotic plateform like using ELF, then by default both binutils and gcc
will be built with LTO and linker plugin support, whether you use gold
or not.

About the build failures you are reporting, you only show the ones in
the "guality" test folders. For me, whatever the gcc/binutils/gdb
versions, these tests are always very flacky and I could never got them
to work at 100% whatever the configuration I use.

What are the "guality" tests ? Simply tests that checks that the
generated debug symbols are fine. In other words, in these tests, gcc
compiles some dummy programs with different options, then start them
with gdb, and tries to put breakpoint and print values. In all the case
I investigated on my side, the issue were that when printing values of
variables in gdb, it often ended up printing "optimized out" rather than
the real value. These tests are highly dependent on the gdb version you
use. So in the end, gcc may be wrong, or maybe it is gcc that cannot
properly read the gcc DWARF data, but the resulting code is fine, just
the debugging may not be.

Apparently I am not the only one where these tests are very flacky. I
discovered that in Google branch of gcc they ended up completely
disabling all these tests because they were always broken at different
places. See https://gcc.gnu.org/ml/gcc-patches/2011-03/msg02120.html
Even today, these tests seems to pass for some gcc developers, but not
for others. Just check the gcc "testresults" mailing list:
https://gcc.gnu.org/ml/gcc-testresults/2016-08/

For example a run executed on gcc 6 x86_64 by H.J. Lu:
https://gcc.gnu.org/ml/gcc-testresults/2016-08/msg00767.html you can see
that a lot of guality tests are failing as well.

So I wouldn't care that much about "guality" tests (on my side, I have
disabled them since they never worked, even when using the very latest
git revision of all involved components).

Cheers,
Romain


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