RFR: 8293291: Simplify relocation of native pointers in archive heap

[Calvin Cheung]

On Thu, 15 Sep 2022 20:49:24 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> Some objects in the archive heap contain native pointers. E.g., archived `java.lang.Class` objects contain a pointer to its `Klass*`.
> 
> At runtime, if the archived metadata are mapped at an alternative address, all of the `Klass*` pointers must be relocated. Instead of doing this in an ad-hoc way, this PR uses a bitmap, `FileMapRegion::ptrmap_view()`, to track the position of all the native pointers.
> 
> This PR is done in preparation for supporting new types of archived heap objects that have native pointers. E.g., `java.lang.invoke.ResolvedMethodName` has a pointer to a `Method*`.
> 
> 
> Notes for reviewers:
> 
> - At dump time, the native pointers are remembered in `HeapShared::mark_native_pointers()`.
> - At runtime, the native pointers are patched in `ArchiveHeapLoader::patch_native_pointers()`.
> - The ad-hoc relocation code has been removed from javaClasses.cpp and systemDictionaryShared.cpp
> - Many of the changes are for renaming from "oopmaps" to "bitmaps": the old code handled only a single type of pointers (oop references). The new code handles two types of bitmaps ("oopmap" is for oop references, "ptrmap" is for native pointers).

I've a few minor comments. Thanks.

src/hotspot/share/cds/filemap.cpp line 1693:

> 1691:       int oopmap_idx = i * 2;
> 1692:       int ptrmap_idx = i * 2 + 1;
> 1693:       space_at(region_idx)->init_bitmaps(bitmaps->at(i*2), bitmaps->at(i*2 + 1));

Please add some comment on oopmap_idx and ptrmap_idx.

Line 1693 could be:
`space_at(region_idx)->init_bitmaps(bitmaps->at(oopmap_idx), bitmaps->at(ptrmap_idx));`

src/hotspot/share/cds/heapShared.cpp line 1848:

> 1846:   }
> 1847: 
> 1848:   log_info(cds, heap)("calculate_ptrmap: marked %d non-null native pointers our of "

typo: our -> out

src/hotspot/share/cds/metaspaceShared.cpp line 907:

> 905:                                                    GrowableArray<ArchiveHeapOopmapInfo>* oopmaps) {
> 906:   for (int i=0; i<regions->length(); i++) {
> 907:     ResourceBitMap oopmap = HeapShared::calculate_oopmap(regions->at(i));

Pre-existing: line 908.
While you're touching this code, please add a space before and after the '=' and '<'.

src/hotspot/share/include/cds.h line 59:

> 57:                               // for alignment purposed.
> 58:   size_t  _oopmap_offset;     // Bitmap for relocating oop fields in archived heap objects.
> 59:                               // (The base address is the botom of the BM region)

typo: botom -> bottom

src/hotspot/share/include/cds.h line 62:

> 60:   size_t  _oopmap_size_in_bits;
> 61:   size_t  _ptrmap_offset;     // Bitmap for relocating native pointer fields in archived heap objects.
> 62:                               // (The base address is the botom of the BM region).

typo: botom -> bottom

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PR: https://git.openjdk.org/jdk/pull/10296