JNI搜索dex中的method

Dex文件格式

dex的定义在DexFile.h里。

typedef struct DexFile {
    /* directly-mapped "opt" header */
    const DexOptHeader* pOptHeader;

    /* pointers to directly-mapped structs and arrays in base DEX */
    const DexHeader*    pHeader;
    const DexStringId*  pStringIds;
    const DexTypeId*    pTypeIds;
    const DexFieldId*   pFieldIds;
    const DexMethodId*  pMethodIds;
    const DexProtoId*   pProtoIds;
    const DexClassDef*  pClassDefs;
    const DexLink*      pLinkData;
 
    /* mapped in "auxillary" section */
    const DexClassLookup* pClassLookup;
 
    /* points to start of DEX file data */
    const u1*           baseAddr;
 
    /* track memory overhead for auxillary structures */
    int                 overhead;
 
    /* additional app-specific data structures associated with the DEX */
    void*               auxData;
} DexFile;

查找dex里class method举例

1、把apk读进内存，释放dex。

deflateDexToBuffer(apkName, &dexBuf, &length)

2、内存里的dex来构造dexfile

DexFile *pDexFile = dexFileParse(dexBuf, length, flags);

3、在dexfile的头文件里查找method个数

int count = (int) pDexFile->pHeader->methodIdsSize;

4、在dexfile里定义了所有method的id

const DexMethodId*  pMethodIds;
循环读取里面包含的所有ids
```c
const DexMethodId* dexGetMethodId(const DexFile* pDexFile, u4 idx) {
    return &pDexFile->pMethodIds[idx];

5、DexMethodId包含了类id和名字id的信息

typedef 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 */
} DexMethodId;

6、根据nameIdx获取字符串
步骤int nameidx->DexStringId* stringidx->****u4 **stringDataOff->char * **

const char* strmethod = dexStringById(pDexFile, mid->nameIdx);

nameidx->stringidx

const DexStringId* pStringId = dexGetStringId(pDexFile, idx);

即&pDexFile->pStringIds[idx];
隐含stringidx->stringDataOff

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

**stringDataOff->char ***
调用dexGetStringData(pDexFile, pStringId);

/* return the const char* string data referred to by the given string_id */
const char* dexGetStringData(const DexFile* pDexFile,
        const DexStringId* pStringId) {
    const u1* ptr = pDexFile->baseAddr + pStringId->stringDataOff;

    // Skip the uleb128 length.
    while (*(ptr++) > 0x7f) /* empty */ ;

    return (const char*) ptr;
}

ps：dex里面用了unsigned leb128，因此要转换
http://fgsink.blog.163.com/blog/static/16716997020124179455097/

7、获取method所在class name类似，不过多了一个步骤。
**步骤classidx->typdidx->****stringidx->stringDataOff->char ***

const char* strclass = dexStringByTypeIdx(pDexFile, mid->classIdx);
/*
 * Direct-mapped "type_id_item".
 */
typedef struct DexTypeId {
    u4  descriptorIdx;      /* index into stringIds list for type descriptor */
} DexTypeId;

8、保存method的name和所在的class

strcpy(pList->methodInfo[i].name, strmethod);
strcpy(pList->methodInfo[i].classtype, strclass);

如何查找

java层调用获取命中包的列表，参数为包的路径。

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checkRiskInfo检查字符串的函数，调用了findtargetstring来查找。

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JNI搜索dex中的method