RFR (XS) 8185160 -XX:DumpLoadedClassList omits graal classes

[Jiangli Zhou]

Hi Ioi,

> On Oct 18, 2017, at 4:54 PM, Ioi Lam <ioi.lam at oracle.com> wrote:
> 
> 
> 
> On 10/17/17 9:04 PM, David Holmes wrote:
>> Hi Ioi,
>> 
>> On 18/10/2017 1:52 PM, Ioi Lam wrote:
>>> http://cr.openjdk.java.net/~iklam/jdk10/8185160-dump-class-list-omits-graal.v01/ 
>>> https://bugs.openjdk.java.net/browse/JDK-8185160
>>> 
>>> Summary:
>>> 
>>> DumpLoadedClassList skips classes that can't be stored into the CDS
>>> archive. For boot and platform loaders, only classes from the JRT image
>>> are listed.
>>> 
>>> The test for "is this class from JRT image" was insufficient. It
>>> checked only classes whose source ends with "...../modules". For the
>>> platform loader, which loads the graal classes, the source is in the
>>> form "jrt:/jdk.internal.vm.compiler".
>>> 
>>> The fix is to also check for a "jrt:" prefix.
>> 
>> So ./share/classfile/classLoader.hpp:
>> 
>> static bool is_jrt(const char* name) { return string_ends_with(name, MODULES_IMAGE_NAME); }
>> 
>> is a badly named function or just plain broken?
>> 
> 
> I've renamed all the is_jrt() functions to is_modules_image(), so it's clear as to what it does.
> 
> See http://cr.openjdk.java.net/~iklam/jdk10/8185160-dump-class-list-omits-graal.v02/ <http://cr.openjdk.java.net/~iklam/jdk10/8185160-dump-class-list-omits-graal.v02/>

The logic looks puzzling. For both NULL class loader and the PlatformClassLoader:

The first if check at line 5938 excludes any classes not in the jimage.

5938           if (!ClassLoader::is_modules_image(stream->source()) && strncmp(stream->source(), "jrt:", 4) != 0) {
5939             skip = true;
5940           }
The second if check at line 5942 skips any classes from the boot append class path loaded by the NULL class loader. The second check skips a subset of the classes that’s already skipped by the first check. The second check is redundant.

5942           if (class_loader == NULL && ClassLoader::contains_append_entry(stream->source())) {
5943             // For the boot loader, also skip all classes that are loaded from the appended entries
5944             skip = true;
5945           }
What about the classes from -Xbootclasspath/a (not in --patch-module and --upgrade-module-path)?

Thanks,
Jiangli

> 
> 
>>> I also restructured the code to make it easier to read -- the nesting of || and && is hard to follow.
>>> 
>>> The original code had a subtle bug with the "!" operator:
>>> 
>>> 5938   if (((class_loader == NULL && !ClassLoader::contains_append_entry(stream->source())) ||
>>> 5939 SystemDictionary::is_platform_class_loader(class_loader)) &&
>>> 5940       !ClassLoader::is_jrt(stream->source())) {
>>> 
>>> So if (class_loader == NULL && ClassLoader::contains_append_entry(stream->source()) was true,
>>> the class would NOT be skipped.
>>> 
>>> The new version removes the "!".
>> 
>> So there should be an updated test to trigger the original bug.
>> 
> 
> I added a test case, but it's in the closed repo for now (since the test case uses utilities in the closed AppCDS tests). This test will be opened as part of JDK-8185996
> 
> Thanks
> - Ioi
> 
>> Thanks,
>> David
>> 
>>> Thanks
>>> - Ioi
>