src/hotspot/share/cds/archiveBuilder.hpp

@@ -25,10 +25,11 @@
  #ifndef SHARE_CDS_ARCHIVEBUILDER_HPP
  #define SHARE_CDS_ARCHIVEBUILDER_HPP
  
  #include "cds/archiveUtils.hpp"
  #include "cds/dumpAllocStats.hpp"
+ #include "memory/metaspace.hpp"
  #include "memory/metaspaceClosure.hpp"
  #include "oops/array.hpp"
  #include "oops/klass.hpp"
  #include "runtime/os.hpp"
  #include "utilities/bitMap.hpp"

@@ -41,13 +42,13 @@
  class FileMapInfo;
  class Klass;
  class MemRegion;
  class Symbol;
  
- // Metaspace::allocate() requires that all blocks must be aligned with KlassAlignmentInBytes.
- // We enforce the same alignment rule in blocks allocated from the shared space.
- const int SharedSpaceObjectAlignment = KlassAlignmentInBytes;
+ // The minimum alignment for non-Klass objects inside the CDS archive. Klass objects need
+ // to follow CompressedKlassPointers::klass_alignment_in_bytes().
+ constexpr size_t SharedSpaceObjectAlignment = Metaspace::min_allocation_alignment_bytes;
  
  // Overview of CDS archive creation (for both static and dynamic dump):
  //
  // [1] Load all classes (static dump: from the classlist, dynamic dump: as part of app execution)
  // [2] Allocate "output buffer"

@@ -445,8 +446,27 @@
      return (Symbol*)current()->get_buffered_addr((address)src_symbol);
    }
  
    void print_stats();
    void report_out_of_space(const char* name, size_t needed_bytes);
+ 
+ #ifdef _LP64
+   // Archived heap object headers (and soon, with Lilliput, markword prototypes) carry pre-computed
+   // narrow Klass ids calculated with the following scheme:
+   // 1) the encoding base must be the mapping start address.
+   // 2) shift must be large enough to result in an encoding range that covers the runtime Klass range.
+   //    That Klass range is defined by CDS archive size and runtime class space size. Luckily, the maximum
+   //    size can be predicted: archive size is assumed to be <1G, class space size capped at 3G, and at
+   //    runtime we put both regions adjacent to each other. Therefore, runtime Klass range size < 4G.
+   // The value of this precomputed shift depends on the class pointer mode at dump time.
+   // Legacy Mode:
+   //    Since nKlass itself is 32 bit, our encoding range len is 4G, and since we set the base directly
+   //    at mapping start, these 4G are enough. Therefore, we don't need to shift at all (shift=0).
+   // TinyClassPointer Mode:
+   //    To cover the 4G, we need the highest possible shift value. That may change in the future, if
+   //    we decide to correct the pre-calculated narrow Klass IDs at load time.
+   static int precomputed_narrow_klass_shift();
+ #endif // _LP64
+ 
  };
  
  #endif // SHARE_CDS_ARCHIVEBUILDER_HPP