We can only load a cds image if UseG1GC, UseCompressedOops and UseCompressedClassPointers are all active. If not, it is supposed to print an info message to UL, see filemap.cpp lines 1484 ff:

  if (!HeapShared::is_heap_object_archiving_allowed()) {
    log_info(cds)("CDS heap data is being ignored. UseG1GC, "
                  "UseCompressedOops and UseCompressedClassPointers are required.");
    return;
  }

For some reason I do not see this message:

thomas@mainframe$ ./images/jdk/bin/java -XX:+UseSharedSpaces -Xlog:cds=trace -XX:-UseCompressedOops
Usage: java [options] <mainclass> [args...]
           (to execute a class)

However, I do see messages if CDS is active:

thomas@mainframe$ ./images/jdk/bin/java -XX:+UseSharedSpaces -Xlog:cds -XX:+UseCompressedOops
[0.006s][info][cds] Mapped region #0 at base 0x800000000 top 0x800003000
[0.006s][info][cds] Mapped region #1 at base 0x800003000 top 0x8003e1000
[0.006s][info][cds] Mapped region #2 at base 0x8003e1000 top 0x800b00000
[0.006s][info][cds] Mapped region #3 at base 0x800b00000 top 0x800b01000
[0.007s][info][cds] CDS archive was created with max heap size = 128M, and the following configuration:
[0.007s][info][cds] narrow_klass_base = 0x0000000800000000, narrow_klass_shift = 3
[0.007s][info][cds] narrow_oop_mode = 0, narrow_oop_base = 0x0000000000000000, narrow_oop_shift = 0
...

So, in general, logging at that point works.

--

seen on Ubuntu 16.4 x64.