sqlite3_open()$\to$openDatabase()$\to$sqlite3_initialize()

功能包含Mutex初始化、Malloc初始化（某些全局变量、静态变量的初始化）、Page Cache（SQLite中处于B树和OS硬盘等操作接口之间，用于加速B树到文件介质之间的读写）初始化、Extra额外初始化……

sqlite3_exec()

1.SQLITE_API int sqlite3_exec(  
2.  sqlite3 *db,                /* The database on which the SQL executes */  
3.  const char *zSql,           /* The SQL to be executed */  
4.  sqlite3_callback xCallback, /* Invoke this callback routine */  
5.  void *pArg,                 /* First argument to xCallback() */  
6.  char **pzErrMsg             /* Write error messages here */  
7.){  
8.  int rc = SQLITE_OK;         /* Return code */  
9.  const char *zLeftover;      /* Tail of unprocessed SQL */  
10.  sqlite3_stmt *pStmt = 0;    /* The current SQL statement */  
11.  char **azCols = 0;          /* Names of result columns */  
12.  int callbackIsInit;         /* True if callback data is initialized */  
13.  
14.  if( !sqlite3SafetyCheckOk(db) ) return SQLITE_MISUSE_BKPT;  
15.  ...  
16.}  

可以看到具体执行SQL语言之前会调用sqlite3SafetyCheckOk()，代码如下

1./* 
2.** Check to make sure we have a valid db pointer.  This test is not 
3.** foolproof but it does provide some measure of protection against 
4.** misuse of the interface such as passing in db pointers that are 
5.** NULL or which have been previously closed.  If this routine returns 
6.** 1 it means that the db pointer is valid and 0 if it should not be 
7.** dereferenced for any reason.  The calling function should invoke 
8.** SQLITE_MISUSE immediately. 
9.** 
10.** sqlite3SafetyCheckOk() requires that the db pointer be valid for 
11.** use.  sqlite3SafetyCheckSickOrOk() allows a db pointer that failed to 
12.** open properly and is not fit for general use but which can be 
13.** used as an argument to sqlite3_errmsg() or sqlite3_close(). 
14.*/  
15.SQLITE_PRIVATE int sqlite3SafetyCheckOk(sqlite3 *db){  
16.  u32 magic;  
17.  if( db==0 ){  
18.    logBadConnection("NULL");  
19.    return 0;  
20.  }  
21.  magic = db->magic;  
22.  if( magic!=SQLITE_MAGIC_OPEN ){  
23.    if( sqlite3SafetyCheckSickOrOk(db) ){  
24.      testcase( sqlite3GlobalConfig.xLog!=0 );  
25.      logBadConnection("unopened");  
26.    }  
27.    return 0;  
28.  }else{  
29.    return 1;  
30.  }  
31.}  

从注释和代码可以看到，这个函数对db指针进行检查，会检测db指针是否为0或者通过Magic检测db指针是否曾被关掉。

也就是说db检查包括检查NULL、检查MAGIC是否OPEN。

sqlite3_close()$\to$sqlite3Close()

再来看一下sqlite3Close的代码如下：

1.static int sqlite3Close(sqlite3 *db, int forceZombie){  
2.  ...  //一些清理工作
3.  
4.  /* Convert the connection into a zombie and then close it. 
5.  */  
6.  db->magic = SQLITE_MAGIC_ZOMBIE;  
7.  sqlite3LeaveMutexAndCloseZombie(db);  
8.  return SQLITE_OK;  
9.}  

发现他会调用sqlite3LeaveMutexAndCloseZombie()来将对db的连接变成zombie，然后关掉，代码如下

1.SQLITE_PRIVATE void sqlite3LeaveMutexAndCloseZombie(sqlite3 *db){  
2.  ... //数据结构的清理维护  
3.  
4.  /* The temp-database schema is allocated differently from the other schema 
5.  ** objects (using sqliteMalloc() directly, instead of sqlite3BtreeSchema()). 
6.  ** So it needs to be freed here. Todo: Why not roll the temp schema into 
7.  ** the same sqliteMalloc() as the one that allocates the database 
8.  ** structure? 
9.  */  
10.  sqlite3DbFree(db, db->aDb[1].pSchema);  
11.  sqlite3_mutex_leave(db->mutex);  
12.  db->magic = SQLITE_MAGIC_CLOSED;  
13.  sqlite3_mutex_free(db->mutex);  
14.  assert( db->lookaside.nOut==0 );  /* Fails on a lookaside memory leak */  
15.  if( db->lookaside.bMalloced ){  
16.    sqlite3_free(db->lookaside.pStart);  
17.  }  
18.  sqlite3_free(db);  
19.}  

发现代码最后有设置db->magic = SQLITE_MAGIC_CLOSED的操作，然后调用sqlite3_free()。

也就是说，MAGIC先设置为ZOMBIE，最后会设置为CLOSED，并且调用sqlite3_free()。

SGX_SQLite未对数据库文件密封

文件操作调用栈如下，备忘一下

ocall_open64(const char * filename, int flags, mode_t mode) (\home\leone\文档\SGX_SQLite\App\ocalls.c:42)
Enclave_ocall_open64(void * pms) (\home\leone\文档\SGX_SQLite\App\Enclave_u.c:248)
libsgx_urts.so!do_ocall(const bridge_fn_t bridge, void * ms) (\home\leone\文档\linux-sgx\psw\urts\linux\sig_handler.cpp:251)
libsgx_urts.so!CEnclave::ocall(CEnclave * const this, const unsigned int proc, const sgx_ocall_table_t * ocall_table, void * ms) (\home\leone\文档\linux-sgx\psw\urts\enclave.cpp:440)
libsgx_urts.so!sgx_ocall(const unsigned int proc, const sgx_ocall_table_t * ocall_table, void * ms, CTrustThread * trust_thread) (\home\leone\文档\linux-sgx\psw\urts\routine.cpp:83)
libsgx_urts.so!stack_sticker() (\home\leone\文档\linux-sgx\psw\urts\linux\enter_enclave.S:244)
__morestack() (\home\leone\文档\linux-sgx\sdk\trts\linux\trts_pic.S:435)
__morestack() (\home\leone\文档\linux-sgx\sdk\trts\linux\trts_pic.S:435)
sgx_ocall(const unsigned int index, void * ms) (\home\leone\文档\linux-sgx\sdk\trts\trts_ocall.cpp:64)
ocall_open64(int * retval, const char * filename, int flags, mode_t mode) (\home\leone\文档\SGX_SQLite\Enclave\Enclave_t.c:909)
open64(const char * filename, int flags) (\home\leone\文档\SGX_SQLite\Enclave\ocall_interface.c:36)
posixOpen(const char * zFile, int flags, int mode) (\home\leone\文档\SGX_SQLite\Enclave\sqlite3.c:30223)
robust_open(const char * z, int f, mode_t m) (\home\leone\文档\SGX_SQLite\Enclave\sqlite3.c:30522)
unixOpen(sqlite3_vfs * pVfs, const char * zPath, sqlite3_file * pFile, int flags, int * pOutFlags) (\home\leone\文档\SGX_SQLite\Enclave\sqlite3.c:35686)
sqlite3OsOpen(sqlite3_vfs * pVfs, const char * zPath, sqlite3_file * pFile, int flags, int * pFlagsOut) (\home\leone\文档\SGX_SQLite\Enclave\sqlite3.c:20291)
sqlite3PagerOpen(sqlite3_vfs * pVfs, Pager ** ppPager, const char * zFilename, int nExtra, int flags, int vfsFlags, void (*)(DbPage *) xReinit) (\home\leone\文档\SGX_SQLite\Enclave\sqlite3.c:51710)
sqlite3BtreeOpen(sqlite3_vfs * pVfs, const char * zFilename, sqlite3 * db, Btree ** ppBtree, int flags, int vfsFlags) (\home\leone\文档\SGX_SQLite\Enclave\sqlite3.c:61376)
openDatabase(const char * zFilename, sqlite3 ** ppDb, unsigned int flags, const char * zVfs) (\home\leone\文档\SGX_SQLite\Enclave\sqlite3.c:143430)
sqlite3_open(const char * zFilename, sqlite3 ** ppDb) (\home\leone\文档\SGX_SQLite\Enclave\sqlite3.c:143598)
ecall_opendb(const char * dbname) (\home\leone\文档\SGX_SQLite\Enclave\Enclave.cpp:21)
sgx_ecall_opendb(void * pms) (\home\leone\文档\SGX_SQLite\Enclave\Enclave_t.c:223)
trts_ecall(uint32_t ordinal, void * ms) (\home\leone\文档\linux-sgx\sdk\trts\trts_ecall.cpp:304)
_random_stack_noinline_wrapper<_status_t, unsigned int, void*, int&, void*&>(_status_t (*)(unsigned int, void *) f) (\home\leone\文档\linux-sgx\common\inc\sgx_random_buffers.h:83)
random_stack_advance<2048u, _status_t, unsigned int, void*, int&, void*&>(_status_t (*)(unsigned int, void *) f) (\home\leone\文档\linux-sgx\common\inc\sgx_random_buffers.h:102)
do_ecall(int index, void * ms, void * tcs) (\home\leone\文档\linux-sgx\sdk\trts\trts_ecall.cpp:438)
enter_enclave(int index, void * ms, void * tcs, int cssa) (\home\leone\文档\linux-sgx\sdk\trts\trts_nsp.cpp:96)
enclave_entry() (\home\leone\文档\linux-sgx\sdk\trts\linux\trts_pic.S:181)
libsgx_urts.so!__morestack() (\home\leone\文档\linux-sgx\psw\urts\linux\enter_enclave.S:77)
libsgx_urts.so!do_ecall(const int fn, const void * ocall_table, const void * ms, CTrustThread * trust_thread) (\home\leone\文档\linux-sgx\psw\urts\linux\sig_handler.cpp:242)
libsgx_urts.so!CEnclave::ecall(CEnclave * const this, const int proc, const void * ocall_table, void * ms, const bool is_switchless) (\home\leone\文档\linux-sgx\psw\urts\enclave.cpp:387)
libsgx_urts.so!_sgx_ecall(const sgx_enclave_id_t enclave_id, const int proc, const void * ocall_table, void * ms, const bool is_switchless) (\home\leone\文档\linux-sgx\psw\urts\routine.cpp:55)
libsgx_urts.so!sgx_ecall(const sgx_enclave_id_t enclave_id, const int proc, const void * ocall_table, void * ms) (\home\leone\文档\linux-sgx\psw\urts\routine.cpp:68)
ecall_opendb(sgx_enclave_id_t eid, const char * dbname) (\home\leone\文档\SGX_SQLite\App\Enclave_u.c:387)
main(int argc, char ** argv) (\home\leone\文档\SGX_SQLite\App\App.cpp:50)