RFR: JDK-8074796 Disabling warnings on clang triggers compiler bug for libunpack

[Erik Joelsson]

Looks good to me.

/Erik

On 2015-03-12 16:04, Magnus Ihse Bursie wrote:
> With JDK-8074096, some warnings produced by libunpack was silenced.
>
> However, it turned out that the version of clang shipped with Xcode 
> 5.1 has some weird behavior, which I would classify as a compiler bug. 
> The generated output differs markedly, if -Wno-foo is present on the 
> command line. Enough to trigger a failure in an Oracle-internal test 
> of libunpack.
>
> Removing the disabled warnings restore the previous behaviour.
>
> While I've spent too much time on this already, I have not been able 
> to pinpoint exactly what triggers this behavior. It seems that all 
> files in libunpack are affected, but no other libs. (However there are 
> also some minor changes in ./java.desktop/libawt_lwawt/OGLPaints.o 
> ./java.desktop/liblcms/cmsps2.o 
> ./java.desktop/libmlib_image/mlib_ImageColorTrue2Index.o which there 
> really should not be.) And it only affects libunpack, not the 
> unpack200 exe which shares part of the code. I have no explanation for 
> this.
>
> The simple solution at this point is to back out the warning changes 
> for clang. There is already a fix on the way to resolve the root cause 
> of this failures. (And yes, I tried running that patch. It did indeed 
> remove the warnings. But when running with the -Wno-foo flags, clang 
> *still* generated broken code.)
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8074796
> Patch inline:
>
> diff --git a/make/lib/Lib-jdk.pack200.gmk b/make/lib/Lib-jdk.pack200.gmk
> --- a/make/lib/Lib-jdk.pack200.gmk
> +++ b/make/lib/Lib-jdk.pack200.gmk
> @@ -42,7 +42,6 @@
>      CFLAGS_release := -DPRODUCT, \
>      DISABLED_WARNINGS_gcc := conversion-null sign-compare 
> format-security \
>          format-nonliteral parentheses, \
> -    DISABLED_WARNINGS_clang := bool-conversion format-security, \
>      DISABLED_WARNINGS_solstudio := truncwarn, \
>      DISABLED_WARNINGS_microsoft := 4267 4018, \
>      MAPFILE := $(JDK_TOPDIR)/make/mapfiles/libunpack/mapfile-vers, \
>
> /Magnus