RFR 8241285(s): [jdk8u] fail to build hotspot with gcc-8.4.0 with or without COMPILER_WARNINGS_FATAL

[Andrew Hughes]

On 19/03/2020 13:59, linzang(臧琳) wrote:
> Dear All,
>      Would you like to help review this tiny fix of build hotspot with gcc-8.4.0?
>      Bug: https://bugs.openjdk.java.net/browse/JDK-8241285
>      Webrev: http://cr.openjdk.java.net/~lzang/8241285/webrev/
> 
>     The fix makes gcc consider COMPILER_WARNINGS_FATAL flag, when it set to false, the warnings from gcc will not be treated as error.
> 
> BRs,
> Lin
> 

I've hit the same warning failure recently too. I thought it was due to
GCC 9, but maybe the same changes were backported to the GCC 8 series.
It can be worked around by passing -Wno-error=stringop-overflow

This doesn't really fix the underlying issue of the
-Werror=stringop-overflow. It turns out I looked into fixing that last
year, as it came up on Fedora builds, due to the use of additional flags:

https://icedtea.classpath.org/bugzilla/show_bug.cgi?id=3696

As to turning off -Werror in the manner suggested in this patch, we've
been doing this for a long time in IcedTea:

https://icedtea.classpath.org/hg/icedtea7-forest/hotspot/rev/c115e0d9e93f

The problem, apart from needing to extend this patch to other platforms,
is that COMPILER_WARNINGS_FATAL was traditionally also used by the JDK
part of the build. So, by making HotSpot respect it, you create a
situation where either both HotSpot & the JDK use -Werror (and the build
fails, because the JDK build is not -Werror clean) or both have to be off.

That was true in 7 anyway. In 8, I can't see any trace of
COMPILER_WARNINGS_FATAL outside the HotSpot tree, due to the new build.
While that solves the above problem, it also means that
COMPILER_WARNINGS_FATAL isn't really integrated into the main build.

I think we can accept this as an 8u only patch (the HotSpot build in 9+
is completely different) if extended to the other platforms, but we also
need to look at backporting --enable/disable-warnings-as-errors so it
can be properly controlled across the entire build.

Thanks,
-- 
Andrew :)

Senior Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

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