DEX file parsing - Method_ IDS resolution

In the last article, I introduced field_ids Parsing , Then the next step is to learn method_ids Parsing .

1. method_ids structure

stay android Of aosp Source code ,method_ids The structure is as follows ：
aosp Source location ：art/libdexfile/dex/dex_file.h

 // Raw method_id_item.
struct MethodId {
    
    dex::TypeIndex class_idx_;   // index into type_ids_ array for defining class
    uint16_t proto_idx_;         // index into proto_ids_ array for method prototype
    dex::StringIndex name_idx_;  // index into string_ids_ array for method name

   private:
    DISALLOW_COPY_AND_ASSIGN(MethodId);
};

StringIndex

class StringIndex {
    
 public:
  uint32_t index_;
  ....  
  ....
};

TypeIndex

class TypeIndex {
    
 public:
  uint16_t index_;
  ....  
  ....
};

from method The following points can be seen from the structure of ：

1. dex::TypeIndex class_idx_： Unsigned int type , Occupy 2 Bytes . Type index list Indexes / Subscript , It means The class of the method
2. uint16_t proto_idx_： Unsigned int type , Occupy 2 Bytes . Prototype index list Indexes / Subscript , It means Prototypes of methods （ Signature ）
3. dex::StringIndex name_idx_： Unsigned int type , Occupy 4 Bytes . String index list Indexes / Subscript , It means Method name

2.010Editor analysis

3.method_ids analysis

 /** *  analysis MethodIds * @param raf * @return */
private static List<MethodId> toParseDexMethodIds(RandomAccessFile raf) {
    
	try {
    
        List<MethodId> methodIdList = new ArrayList<>();
        // Get the file offset to the method index list 
        int method_ids_off = mDexHeader.getMethod_ids_off();
        // Get the size of the method index list 
        int method_ids_size = mDexHeader.getMethod_ids_size();
        // Offset to method index list position 
        raf.seek(method_ids_off);
        for (int i = 0; i < method_ids_size; i++) {
    
            // obtain   The class name of the class where this field is located , Class name idx In the type index list 
            int class_idx = NumConversion.byteToInt(readData(raf, 2), false);
            // obtain   Prototype of this field （ Method signature ）, Prototype idx In the prototype index list 
            int proto_idx = NumConversion.byteToInt(readData(raf,2),false);
            // obtain   The method name of this field , Method name idx In the string index list 
            int name_idx = NumConversion.byteToInt(readData(raf,4),false);

            // Print data 
            // Get method name 
            StringId name_string_id = mStringIds.get(name_idx);
            String name_string = new String(name_string_id.getData());
            // Get class 
            TypeId class_type_id = mTypeIds.get(class_idx);
            StringId class_type_string_id = mStringIds.get(class_type_id.getTypeDescriptorIdx());
            String class_type_string = new String(class_type_string_id.getData());
            // Get return value type 
            ProtoId proto_id = mProtyIds.get(proto_idx);
            TypeId return_type_id = mTypeIds.get(proto_id.getReturnIdx());
            StringId return_type_string_id = mStringIds.get(return_type_id.getTypeDescriptorIdx());
            String return_type_string = new String(return_type_string_id.getData());
            // Get a list of method parameters 
            StringBuilder sb = new StringBuilder("(");
            for (int j=0;j<proto_id.getParameter_size();j++) {
    
                int parame_idx = proto_id.getParameterIdxs()[j];
                TypeId parame_type_id = mTypeIds.get(parame_idx);
                StringId parame_string_id = mStringIds.get(parame_type_id.getTypeDescriptorIdx());
                sb.append(new String(parame_string_id.getData()));
                if (j == proto_id.getParameter_size()-1) {
    
                    sb.append(")");
                }else if (proto_id.getParameter_size() != 1) {
    
                    sb.append(", ");
                }
            }
            if (proto_id.getParameter_size() == 0) sb.append(")");

            // Create entity class 
            MethodId methodId = new MethodId();
            methodId.setClass_idx(class_idx);
            methodId.setProto_idx(proto_idx);
            methodId.setName_idx(name_idx);
            methodIdList.add(methodId);

            System.out.println(i+"  stay  " + class_type_string + " Class ,  Method ：" +return_type_string+" "+name_string+sb.toString());
        }
        return methodIdList;
    }catch (Exception e) {
    
        e.printStackTrace();
    }

    return null;
}

public static byte[] readData(RandomAccessFile raf,int limit) {
    
    byte[] buff = new byte[limit];
    try {
    
        raf.read(buff);
    } catch (IOException e) {
    
        e.printStackTrace();
    }
    return buff;
}

Entity class MethodId

public class MethodId {
    
    private int class_idx;
    private int proto_idx;
    private int name_idx;

    public int getClass_idx() {
    
        return class_idx;
    }

    public void setClass_idx(int class_idx) {
    
        this.class_idx = class_idx;
    }

    public int getProto_idx() {
    
        return proto_idx;
    }

    public void setProto_idx(int proto_idx) {
    
        this.proto_idx = proto_idx;
    }

    public int getName_idx() {
    
        return name_idx;
    }

    public void setName_idx(int name_idx) {
    
        this.name_idx = name_idx;
    }
}

Tool class NumConversion

public class NumConversion {
    

    public static int byteToInt(byte[] bytes,boolean isBigEndian) {
    
        if (bytes.length <=0 || bytes.length > 4) return -1;
        int result = 0;
        for (int i=0;i<bytes.length;i++) {
    
            int b ;
            if(isBigEndian){
    
                b = (bytes[i] & 0xFF) << (8*(bytes.length-1-i));
            }else {
    
                b = (bytes[i] & 0xFF) << (8*i);
            }
            result = result | b;
        }
        return result;
    }
}

asjhan for Android reverse