[RFR] JDK-8156980: Hotspot build doesn't have -std=gnu++98 gcc option

[Andrew Hughes]

----- Original Message -----
> Catching up ...
> 
> On 11/07/2016 7:05 AM, Andrew Hughes wrote:
> >
> >
> > ----- Original Message -----
> >>> On Jul 8, 2016, at 2:38 AM, Erik Joelsson <erik.joelsson at oracle.com>
> >>> wrote:
> >>>
> >>> Hello,
> >>>
> >>> This looks good except for the change in toolchain.m4, which looks like
> >>> it
> >>> might actually break cross compilation by overriding the value for
> >>> compiler version for the build compiler using the target compiler. With
> >>> this change we basically have:
> >>>
> >>> if cross compilation
> >>>  TOOLCHAIN_PREPARE_FOR_VERSION_COMPARISONS([BUILD_], [OPENJDK_BUILD_])
> >>> else
> >>>  ...
> >>> fi
> >>> TOOLCHAIN_PREPARE_FOR_VERSION_COMPARISONS([], [OPENJDK_BUILD_])
> >>>
> >>> The problem you are trying to solve is that in the case of not cross
> >>> compilation, the TOOLCHAIN_PREPARE_FOR_VERSION_COMPARISONS macro wasn't
> >>> called with "OPENJDK_BUILD_". Kim's suggested patch was to add the call
> >>> in
> >>> the else clause.
> >>
> >> Good catch!  I totally missed that when reviewing.
> >>
> >>
> > Yes, good catch! The indenting on the bug report must have confused me.
> >
> > Fixed version:
> >
> > http://cr.openjdk.java.net/~andrew/8156980/webrev.06/root/
> > http://cr.openjdk.java.net/~andrew/8156980/webrev.06/hotspot
> 
> I was glad to see you realized that parts of the hotspot build (libjsig,
> libdtrace) only deal with C programs not C++ and so don't want and
> should not have a C++ setting passed. But that then begs the question in
> the main build in flags.m4 why we have:
> 
>   $2JVM_CFLAGS="${$2JVM_CFLAGS} ${$2CXXSTD_CXXFLAG}"
> 
> which again adds a C++ related flags to what should be the C compilation
> flags ??
> 

You'd think so, but for some reason, the HotSpot build has always called the
C++ compiler flags 'CFLAGS'. There is no JVM_CXXFLAGS.

The same behaviour was true with the old build; we had to pass these options
down to HotSpot in EXTRA_CFLAGS.

JVM_CFLAGS is the main variable used in the HotSpot build (see make/lib/CompileJvm.gmk).
The only C files in the HotSpot tree are for libsaproc, jsig and DTrace,
all of which are handled by separate makefiles. The only one to use JVM_CFLAGS is
make/lib/CompileDtracePostJvm.gmk, where it is used for a single C++ file, generateJvmOffsets.cpp:

        generateJvmOffsets.cpp_CXXFLAGS := $(JVM_CFLAGS) -mt -xnolib -norunpath, \
        generateJvmOffsetsMain.c_CFLAGS := -library=%none -mt -m64 -norunpath -z nodefs, \

Thus, it seems JVM_CFLAGS is JVM_CXXFLAGS in all but name.

If -std=gnu++98 does get passed to the C compiler, it produces a warning:

cc1: warning: command line option '-std=gnu++98' is valid for C++/ObjC++ but not for C

I don't see this at all for this patch on OpenJDK 9. It does appear in the backport
to 8u [0], because the aforementioned C code in the old HotSpot build does use the
same CFLAGS there.

> Thanks,
> David
> -----
> 
> > HotSpot webrev is unchanged.
> >
> > Thanks,
> >
> 

[0] http://mail.openjdk.java.net/pipermail/jdk8u-dev/2016-July/005690.html
-- 
Andrew :)

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

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