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  25 
  26 #ifndef CPU_S390_RELOCINFO_S390_HPP
  27 #define CPU_S390_RELOCINFO_S390_HPP
  28 
  29 //----------------------------
  30 //  relocInfo layout
  31 //----------------------------
  32 
  33 // This description should be contained in code/relocInfo.hpp
  34 // but was put here to minimize shared code diffs.
  35 
  36 // Relocation information for a nmethod is stored in compressed
  37 // form in an array of element type short int (16 bits).
  38 // Each array element constitutes one relocInfo record.
  39 // The layout of one such record is described here.
  40 
  41 // +------------+---+---+------------------------------+
  42 // |    type    |  fmt  |      offset/offset_unit      |
  43 // +------------+---+---+------------------------------+
  44 //
  45 // |<-- value_width (16) ----------------------------->|
  46 // |<type_width>|<-- nontype_width (12) -------------->|
  47 //      (4)
  48 // |            |<--+-->|<-- offset_width (10) ------->|
  49 //              /       \
  50 //             /   (2)   \
  51 //            /<--format->\
  52 //            |    width  |
  53 
  54 
  55 // only for type == data_prefix_tag:
  56 // +------------+---+---+------------------------------+
  57 // |    type    |   |              data                |
  58 // +------------+---+---+------------------------------+
  59 // |     15     |<->|<-- datalen_width (11) ---------->|
  60 //                |
  61 //                +--datalen_tag (1)
  62 
  63 // relocType
  64 //   The type field holds a value of relocType (which is
  65 //   an enum of all possible relocation types). Currently,
  66 //   there are 16 distinct relocation types, requiring
  67 //   type_width to be (at least) 4.
  68 // relocFormat
  69 //   The format field holds a value of relocFormat (which is
  70 //   an enum of all possible relocation formats). Currently,
  71 //   there are 4 distinct relocation formats, requiring
  72 //   format_width to be (at least) 2.
  73 // offset
  74 //   Each relocInfo is related to one specific address in the CodeBlob.
  75 //   The address always points to the first byte of the target instruction.
  76 //   It does NOT refer directly to the relocation subfield or embedded constant.
  77 //   offset contains the distance of this relocInfo from the previous one.
  78 //   offset is scaled by offset_unit (the platform-specific instruction
  79 //   alignment requirement) to maximize the encodable distance.
  80 //   To obtain the absolute address in the CodeBlob the relocInfo is
  81 //   related to, you have to iterate over all relocInfos from the
  82 //   beginning, and then use RelocIterator::addr() to get the address.
  83 
  84 // relocType == data_prefix_tag
  85 //   These are relocInfo records containing inline data that belongs to
  86 //   the next non-data relocInfo record. Usage of that inline data is
  87 //   specific and private to that relocInfo record.
  88 //   For details refer to code/relocInfo.hpp
  89 
  90 
  91   // machine-dependent parts of class relocInfo
  92  private:
  93   enum {
  94     // Instructions are HW (2-byte) aligned on z/Architecture.
  95     offset_unit        =  2,
  96 
  97     // Encodes Assembler::disp32_operand vs. Assembler::imm64_operand.
  98     // (Assembler::call32_operand is used on call instructions only.)
  99     format_width       =  2
 100   };
 101 
 102  public:
 103 
 104   enum relocFormat {
 105     no_format           = 0,
 106     uncompressed_format = 0,  // Relocation is for a regular oop.
 107     compressed_format   = 1,  // Relocation is for a narrow (compressed) oop or klass.
 108                               // Similar to relocInfo::narrow_oop_in_const.
 109     pcrel_addr_format   = 2,  // Relocation is for the target LOCATION of a pc-relative instruction.
 110     pcrel_data_format   = 3   // Relocation is for the target data of a pc-relative instruction.
 111   };
 112 
 113   // This platform has no oops in the code that are not also
 114   // listed in the oop section.
 115   static bool mustIterateImmediateOopsInCode() { return false; }
 116 
 117 #endif // CPU_S390_RELOCINFO_S390_HPP