StructMetadata

StructMetadata的内存布局

图

• Swift的StructMetadata内存布局图 = Swift ValueMetadata Memory Layout
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文字

• Swift的StructMetadata的内存布局
  • [-0x08] = ValueWitnessTable* vwt;
  • [+0x00] = int64 kind // 是固定的：0x200
  • [+0x08] = StructDescriptor* description
    • StructDescriptor
      • FieldDescriptor
        • FieldRecord

举例

ConcreteConfigPrimitiveBox的StructDescriptor

内存值：

(lldb) x/16gw 0x000000010771431c
0x10771431c: 0x000000d1 0xffffffdc 0xffe75bcc 0xfd6669b4
0x10771432c: 0x00000000 0x00000001 0x00000004 0x00a2c760
0x10771433c: 0xffe75bd4 0x00010001 0x00000002 0x00000080
0x10771434c: 0x00000080 0x000a5870 0xfffffe78 0x000000c2

对应着IDA中的汇编：

__constg_swiftt:0000000102DF831C ; nominal type descriptor for MainAppLibrary.ConcreteConfigPrimitiveBox
__constg_swiftt:0000000102DF831C $s14MainAppLibrary26ConcreteConfigPrimitiveBoxVMn StructDescriptor <0xD1, stru_102DF82FC - ., aConcreteconfig - ., \
__constg_swiftt:0000000102DF831C                                         ; DATA XREF: type metadata accessor for ConcreteConfigPrimitiveBox↑o
__constg_swiftt:0000000102DF831C                                         ; __swift5_types:0000000102EA5EAC↓o ...
__constg_swiftt:0000000102DF831C                                   $s14MainAppLibrary26ConcreteConfigPrimitiveBoxVMa - .,\ ; type metadata accessor for ConcreteConfigPrimitiveBox ...
__constg_swiftt:0000000102DF831C                                   $s14MainAppLibrary26ConcreteConfigPrimitiveBoxVMn.FieldDescriptor - .,\
__constg_swiftt:0000000102DF831C                                   1, 4>

->

• StructDescriptor的例子：ConcreteConfigPrimitiveBox
  • struc : sizeof=0x1C == 0x000000010771431c == IDA的 0x0000000102df831c
    • [0x00~0x03] = Flags
      • 0x000000d1
    • [0x04~0x07] = Parent
      • 0xffffffdc
        • stru_102DF82FC - .
        • = 0x102DF82FC - (0x0000000102df831c + 0x4)
        • = 0x102DF82FC - 0x0000000102df8320
        • = 0xFFFFFFDC
    • [0x08~0x0B] = Name
      • 0xffe75bcc
        • aConcreteconfig - .
          • aConcreteconfig == "ConcreteConfigPrimitiveBox"
        • = 0x102C6DEF0 - (0x0000000102df831c + 0x8)
        • = 0xFFE75BCC
    • [0x0C~0x0F] = AccessFunction = AccessFunctionPtr
      • 0xfd6669b4
        • $s14MainAppLibrary26ConcreteConfigPrimitiveBoxVMa - .
        • = 0x10045ECDC - (0x0000000102df831c + 0xC)
        • = 0xFD6669B4
    • [0x10~0x13] = FieldDescriptor == Fields
      • 0x00000000
        • $s14MainAppLibrary26ConcreteConfigPrimitiveBoxVMn.FieldDescriptor - .
        • = 0x0000000102df832c - (0x0000000102df831c + 0x10)
        • = 0
    • [0x14~0x17] = NumFields
      • 0x00000001
        • 这个结构体只有一个字段=属性property=域field ？
        • 好像是：field offset vector length = 1
          • 此处是有1个field offset vector的
    • [0x18~0x1B] = FieldOffsetVectorOffset
      • 0x00000004
        • The offset of the field offset vector for this struct's stored properties in its metadata
          • 此处的field offset vector的offset是4