RFR(M): 8204965: Fix '--disable-cds' and disable CDS on AIX by default

[Thomas Stüfe]

Hi Volker,

http://cr.openjdk.java.net/~simonis/webrevs/2018/8204965/make/autoconf/hotspot.m4.udiff.html

Seems like a roundabout way to have a platform specific default value.

Why not determine a default value beforehand:

if test "x$OPENJDK_TARGET_OS" = "xaix"; then
  ENABLE_CDS_DEFAULT="false"
else
  ENABLE_CDS_DEFAULT=true"
fi

AC_ARG_ENABLE([cds], [AS_HELP_STRING([--enable-cds@<:@=yes/no/auto@:>@],
 [enable class data sharing feature in non-minimal VM. Default is
${ENABLE_CDS_DEFAULT}.])])

and so on?

See also what we did for "8202325: [aix] disable warnings-as-errors by default".

--

http://cr.openjdk.java.net/~simonis/webrevs/2018/8204965/src/hotspot/share/classfile/javaClasses.cpp.udiff.html

Here, do we really need to exclude this from compiling,
DumpSharedSpaces = false is not enough?


Best Regards, Thomas

On Thu, Jun 14, 2018 at 4:26 PM, Volker Simonis
<volker.simonis at gmail.com> wrote:
> Hi,
>
> can I please have a review for the following fix:
>
> http://cr.openjdk.java.net/~simonis/webrevs/2018/8204965/
> https://bugs.openjdk.java.net/browse/JDK-8204965
>
> CDS does currently not work on AIX because of the way how we
> reserve/commit memory on AIX. The problem is that we're using a
> combination of shmat/mmap depending on the page size and the size of
> the memory chunk to reserve. This makes it impossible to reliably
> reserve the memory for the CDS archive and later on map the various
> parts of the archive into these regions.
>
> In order to fix this we would have to completely rework the memory
> reserve/commit/uncommit logic on AIX which is currently out of our
> scope because of resource limitations.
>
> Unfortunately, I could not simply disable CDS in the configure step
> because some of the shared code apparently relies on parts of the CDS
> code which gets excluded from the build when CDS is disabled. So I
> also fixed the offending parts in hotspot and cleaned up the configure
> logic for CDS.
>
> Thank you and best regards,
> Volker
>
> PS: I did run the job through the submit forest
> (mach5-one-simonis-JDK-8204965-20180613-1946-26349) but the results
> weren't really useful because they mention build failures on linux-x64
> which I can't reproduce locally.