RFR: 8244847: Linux/PPC: runtime/CompressedOops/CompressedClassPointers: smallHeapTest fails

[Richard Reingruber]

This is an XS sized patch to get a zerobased compressed class space on
Linux/PPC64 if a heap up to 2g size is configured and CDS is disabled.

On Linux 4.1.42 and higher we fail to get a zerobased CCS because just one
attempt is made to place the CCS right after the heap which will be at 4g
(ELF_ET_DYN_BASE) but there the java launcher is already mapped.

This change reuses the search already implemented for AARCH64.

                  Master without Fix                               Master with Fix

-Xmx   Narrow klass base     Compressed Class Space    Narrow klass base     Compressed Class Space
----------------------------------------------------------------------------------------------------
512m   0x00007fff00000000 !  0x00007fff00000000        0x0000000000000000    0x0000000200000000
  1g   0x00007fff14000000 !  0x00007fff14000000        0x0000000000000000    0x0000000200000000
  2g   0x00007fff30000000 !  0x00007fff30000000        0x0000000000000000    0x0000000200000000
  3g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
  4g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
  8g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
 12g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
 16g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
 20g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
 24g   0x0000000000000000    0x00000007c0000000        0x0000000000000000    0x00000007c0000000
 28g   0x0000001702000000    0x0000001702000000        0x0000001702000000    0x0000001702000000
 32g   0x0000000000000000    0x0000000080000000        0x0000000000000000    0x0000000080000000
 40g   0x0000000000000000    0x0000000080000000        0x0000000000000000    0x0000000080000000
 48g   0x0000000000000000    0x0000000080000000        0x0000000000000000    0x0000000080000000

-------------

Commit messages:
 - 8244847: Linux/PPC: runtime/CompressedOops/CompressedClassPointers: smallHeapTest fails

Changes: https://git.openjdk.java.net/jdk/pull/1512/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1512&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8244847
  Stats: 11 lines in 2 files changed: 9 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1512.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1512/head:pull/1512

PR: https://git.openjdk.java.net/jdk/pull/1512