kodi: disable compiler optimization for arm (fixes segmentation fault)

[escalade]

With OPTIMIZATIONS=normal set in project options, Kodi crashes with segmentation fault when adding to the library. Reproduced only on arm/RPi2, Generic seems fine. Using -Os instead of -O2 avoids the issue.

References:

https://forum.libreelec.tv/thread-302-post-9754.html#pid9754
http://forum.odroid.com/viewtopic.php?f=62&t=20345

[MilhouseVH]

Is this fixed by gcc-6?

[escalade]

Yes, but with GCC6 there's an issue with reading FLAC tags (for generic as well). Was thinking to test 6.2 today.

[popcornmix]

Sounds like a compiler bug, so moving backwards/forwards to a version that doesn't have the bug may be a better choice than changing optimisation level (which could affect performance and will probably be forgotten about long after the compiler bug is fixed).

[popcornmix]

Obviously a newer gcc may fix this bug and introduce a new one.
But, no guarantee that -Os doesn't fix this bug and introduce a new one.

I guess bumping gcc to latest - check if this bug is fixed and if so get the new build tested in Milhouse/nightly builds to try to spot any regressions.

[escalade]

I agree, except when a new compiler introduces more bugs :) Other than the FLAC issue mentioned 6.1 works fine though (with a few minor fixes). It does however drastically increase build time.

[escalade]

@popcornmix Actually -Os is the default so it will surely not introduce new bugs. This change only reverts the Kodi package to default optimization when OPTIMIZATIONS=normal (-O2) is set in the project options. Eveery package is compiled with -Os by default.

[MilhouseVH]

Yes, the default OPTIMIZATIONS for all projects is size:

neil@nm-linux:~/projects/LibreELEC.tv/projects$ grep -r OPTIMIZATIONS
WeTek_Core/options:    OPTIMIZATIONS="size"
imx6/options:    OPTIMIZATIONS="size"
RPi/options:    OPTIMIZATIONS="size"
Odroid_C2/options:    OPTIMIZATIONS="size"
Virtual/options:    OPTIMIZATIONS="size"
WeTek_Play/options:    OPTIMIZATIONS="size"
Generic/options:    OPTIMIZATIONS="size"
RPi2/options:    OPTIMIZATIONS="size"
WeTek_Hub/options:    OPTIMIZATIONS="size"

The two supported options are normal and size: https://github.com/LibreELEC/LibreELEC.tv/blob/master/config/optimize#L1-L9

if [ "$OPTIMIZATIONS" = normal ];then
  GCC_OPTIM="-O2"
  LD_OPTIM=""
fi

if [ "$OPTIMIZATIONS" = size ];then
  GCC_OPTIM="-Os -fexcess-precision=fast"
  LD_OPTIM="-Wl,--as-needed"
fi

so this change would have no effect whatsoever on current builds that use the default OPTIMIZATIONS (size), which may help explain why it's such a rarely seen issue (never seen it reported by users one of my builds, for instance). This is only an issue for custom builds that use the non-standard normal optimisation.

I'd personally rather see if we can work around this with a compiler bump, either gcc 6.1.0 or the future 6.2,

[escalade]

Might be good to have in the 7.0 branch?

[stefansaraev]

OPTIMIZATIONS=normal serves no real purpose and you should completely remove it.

EDIT: you should remove any OPTIMIZATIONS, and always use -Os

nijna edit: you should also remove -fexcess-precision=..

[escalade]

The purpose is faster code.

[stefansaraev]

I know what it is, @popcornmix but too many things may (and will) interfere right now :)

I dont think -O2 gives you much speed compared to -Os.

[escalade]

I've compiled with -O2 for quite a while (gcc 5.3, 5.4 and 6.1) both for generic/rpi and so far this is the only issue I've come across. The improvement can be neglible but can also be much faster for certain code. Lots of distributions use -O2 as default (Arch for example), and there's plenty of benchmarks that proves it's worth.

[stefansaraev]

as you wish ;)

[escalade]

Don't confuse me for popcornmix btw, we just have the same cool avatar ;)

[stefansaraev]

ouch ;)

[stefansaraev]

@escalade

Yes, but with GCC6 there's an issue with reading FLAC tags (for generic as well). Was thinking to test 6.2 today.

can you share a sample ?

[chewitt]

Closing as superseded by #696