Integrated: 8262376: ReplaceCriticalClassesForSubgraphs.java fails if --with-build-jdk is used

[Ioi Lam]

On Thu, 29 Apr 2021 00:32:51 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> When CDS tries to load sun.util.resources.cldr.provider.CLDRLocaleDataMetaInfo from the classlist, the VM has already finished the "early" bootup phase. To load this class, the module system tries to create an instance of jdk.internal.module.SystemModuleFinders$SystemModuleReader and store that into the ArchivedBootLayer. However, the SystemModuleReader class is also not yet loaded, so the VM loads it on demand. As a result, SystemModuleReader is treated as a "non-early class".
> 
> The problem is now ArchivedBootLayer refers to a non-early class. At runtime, if JVMTI ClassLoadHook is enabled, HeapShared will refuse to load ArchivedBootLayer from the archived heap. The reason is explained by this in heapShared.cpp:
> 
> 
> // Note: if a ArchivedKlassSubGraphInfoRecord contains non-early classes, and JVMTI
> // ClassFileLoadHook is enabled, it's possible for this class to be dynamically replaced. In
> // this case, we will not load the ArchivedKlassSubGraphInfoRecord and will clear its roots.
> 
> 
> However, this doesn't make sense for ArchivedBootLayer -- it's loaded in the early phase at runtime, so any classes referenced by ArchivedBootLayer will also be loaded in the early phase. This means JVMTI ClassLoadHook cannot replace SystemModuleReader.
> 
> Hence, the fix is simple -- for any classes referenced by the 3 "full-module-graph" subgraphs, we always treat them as "early" classes, regardless of when they are loaded during dump time.
> 
> 
> // Entry fields for subgraphs archived in the open archive heap region (full module graph).
> static ArchivableStaticFieldInfo fmg_open_archive_subgraph_entry_fields[] = {
>   {"jdk/internal/loader/ArchivedClassLoaders", "archivedClassLoaders"},
>   {"jdk/internal/module/ArchivedBootLayer", "archivedBootLayer"},
>   {"java/lang/Module$ArchivedData", "archivedData"},
> };
> 
> 
> The validate the fix, I modified the test case to always load CLDRLocaleDataMetaInfo during dump time. The test failed without the fix and passed with the fix.

This pull request has now been integrated.

Changeset: 2c381e0f
Author:    Ioi Lam <iklam at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/2c381e0f8d5777d289a6eb410d66d8221c7d9d1b
Stats:     19 lines in 2 files changed: 12 ins; 3 del; 4 mod

8262376: ReplaceCriticalClassesForSubgraphs.java fails if --with-build-jdk is used

Reviewed-by: dholmes, minqi, ccheung

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PR: https://git.openjdk.java.net/jdk/pull/3780