RFR(S) 8244536 cds/DeterministicDump.java failed: File content different

[Thomas Stüfe]

Hi Ioi,

Could is_heap_object_archiving_allowed() be different between runtime and
dumptime?
If yes, would it make sense to explicitly reserve values for "header field
is invalid"? Since zero can be ambiguous _narrow_oop_mode=0 is Unscaled).

..Thomas

On Wed, May 13, 2020 at 7:52 PM Ioi Lam <ioi.lam at oracle.com> wrote:

>
>
> On 5/13/20 10:42 AM, Yumin Qi wrote:
> > HI, Ioi
> >
> >   I have a question here:
> >
> >    _version = CURRENT_CDS_ARCHIVE_VERSION;
> >    _alignment = alignment;
> >    _obj_alignment = ObjectAlignmentInBytes;
> >    _compact_strings = CompactStrings;
> > + if (HeapShared::is_heap_object_archiving_allowed()) {
> >    _narrow_oop_mode = CompressedOops::mode();
> >    _narrow_oop_base = CompressedOops::base();
> >    _narrow_oop_shift = CompressedOops::shift();
> > + _heap_end = CompressedOops::end();
> > + }
> >    _compressed_oops = UseCompressedOops;
> >    _compressed_class_ptrs = UseCompressedClassPointers;
> >    _max_heap_size = MaxHeapSize;
> >    _narrow_klass_shift = CompressedKlassPointers::shift();
> > - if (HeapShared::is_heap_object_archiving_allowed()) {
> > - _heap_end = CompressedOops::end();
> > - }
> >
> > _heap_end seems not calculated if heap object not archived.
> >
>
> Hi Yumin,
>
> Thanks for your comment.
>
> The header is cleared to zeros in here:
>
> FileMapInfo::FileMapInfo(bool is_static) {
>    ...
>    _header = (FileMapHeader*)os::malloc(header_size, mtInternal);
>    memset((void*)_header, 0, header_size);
>
> So if heap objects are not archived, _narrow_oop_mode, _narrow_oop_base,
> _narrow_oop_shift and _heap_end will all be zeros. These fields will not
> be used during runtime.
>
> Thanks
> - Ioi
>
>
> >
> >
> > Thanks
> > Yumin
> >
> > On 5/11/20 2:00 PM, Ioi Lam wrote:
> >> https://bugs.openjdk.java.net/browse/JDK-8244536
> >>
> http://cr.openjdk.java.net/~iklam/jdk15/8244536-DeterministicDump-fails-on-windows.v01/
> >>
> >>
> >> I fixed 2 issues that are likely to happen on Windows due to
> >> it aggressive ASLR policy (address space layout randomization).
> >> These would cause the CDS archive to have non-deterministic
> >> contents:
> >>
> >> [1] Don't save the _narrow_oop_{mode,shift,base} header fields
> >>     for platforms (including Windows) that don't support heap
> >>     archiving, as these fields would be useless anyway.
> >>
> >>     This was the cause of the failure cases in the bug report.
> >>
> >> [2] Fixed a hashtable that would lay out differently if
> >>     the archive was relocated during -Xshare:dump. This is also
> >>     likely to happen on Windows but is not as frequent as #1.
> >>
> >>     Added test case for [2] in DeterministicDump.java (using
> >>     -XX:ArchiveRelocationMode=1).
> >>
> >>
> >> Test on mach5 with tiers 1/2/3.
> >>
> >> Thanks
> >> - Ioi
> >
>
>