dex文件格式

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dex文件格式

数据结构

u1：等同于uint8_t，表示1字节的无符号数
u2
u4
u8
sleb128：有符号LEB128，可变长度15字节
uleb128：无符号LEB128，可变长度15字节
uleb128p1：无符号LEB128指加1，可变长度1~5字节

uleb128：

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00001001 10000111 01100101  624485的2进制表示
 0100110  0001110  1100101  把2进制的表示的bit扩展为能被7整除（不足的加0）
 0100110  0001110  1100101  再以7-bit为一组进行分组
00100110 10001110 11100101  把第一组+0扩展为8bit，而其余的都+1扩展为8bit
    0x26     0x8E     0xE5  结果表示位16进制
            0xE5 0x8E 0x26  最终在内存中的表示

sleb128：

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11110110 01111000 10011011  -624485的2进制表示(呵呵，负数在计算机中是如何表示的，大家没有忘吧：）补码啊补码)
     101100111100010011011  把2进制的表示扩展为能被7整除
  101001  1110001  0011011  再以7-bit为一组进行分组
01011001 11110001 10011011  把第一组+0扩展为8bit，而其余的都根据原整形数的符号位来扩展为8bit（所以这里最后两个7bit组都是+1来扩展的）
    0x59     0xf1     0x9b  结果表示位16进制
            0x9b 0xf1 0x59  最终在内存中的表示

文件结构

dexformat

header:

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/*
 * Direct-mapped "header_item" struct.
 */
struct DexHeader {
    u1  magic[8];           /* includes version number */
    u4  checksum;           /* adler32 checksum */
    u1  signature[kSHA1DigestLen]; /* SHA-1 hash */
    u4  fileSize;           /* length of entire file */
    u4  headerSize;         /* offset to start of next section */
    u4  endianTag;
    u4  linkSize;
    u4  linkOff;
    u4  mapOff;
    u4  stringIdsSize;
    u4  stringIdsOff;
    u4  typeIdsSize;
    u4  typeIdsOff;
    u4  protoIdsSize;
    u4  protoIdsOff;
    u4  fieldIdsSize;
    u4  fieldIdsOff;
    u4  methodIdsSize;
    u4  methodIdsOff;
    u4  classDefsSize;
    u4  classDefsOff;
    u4  dataSize;
    u4  dataOff;
};

dexformat

string_ids: the list of DexStringId

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struct DexStringId {
    u4 stringDataOff;      /* file offset to string_data_item */
};

type_ids: the list of DexTypeId

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struct DexTypeId {
    u4  descriptorIdx;      /* index into stringIds list for type descriptor */
};

proto_ids: the list ofDexProtoId

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struct DexProtoId {
    u4  shortyIdx;          /* index into stringIds for shorty descriptor */
    u4  returnTypeIdx;      /* index into typeIds list for return type */
    u4  parametersOff;      /* file offset to type_list for parameter types */
};

field_ids: the list of DexFieldId

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struct DexFieldId {
    u2  classIdx;           /* index into typeIds list for defining class */
    u2  typeIdx;            /* index into typeIds for field type */
    u4  nameIdx;            /* index into stringIds for field name */
};

method_ids: the list of DexMethodId

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struct DexMethodId {
    u2  classIdx;           /* index into typeIds list for defining class */
    u2  protoIdx;           /* index into protoIds for method prototype */
    u4  nameIdx;            /* index into stringIds for method name */
};

class_defs: the list of DexClassDef

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struct DexClassDef {
    u4  classIdx;           /* index into typeIds for this class */
    u4  accessFlags;
    u4  superclassIdx;      /* index into typeIds for superclass */
    u4  interfacesOff;      /* file offset to DexTypeList */
    u4  sourceFileIdx;      /* index into stringIds for source file name */
    u4  annotationsOff;     /* file offset to annotations_directory_item */
    u4  classDataOff;       /* file offset to class_data_item */
    u4  staticValuesOff;    /* file offset to DexEncodedArray */
};

map：the list of DexMapItem and the list size

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struct DexMapList {
    u4  size;               /* #of entries in list */
    DexMapItem list[1];     /* entries */
};
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struct DexMapItem {
    u2 type;              /* type code (see kDexType* above) */
    u2 unused;
    u4 size;              /* count of items of the indicated type */
    u4 offset;            /* file offset to the start of data */
};