【PHP问题定位】修改数据库字段导致的fpm的coredump问题定位

摘要：顺风车运营研发团队黄桃背景线上零星会出现进程及进程占用内存超过限制等报警告，并且两者报警的时间上往往都比较接近，如下原因分析时间上接近，那么出现两者报警的原因有可能是相同的，登录机器调试生成文件

顺风车运营研发团队 黄桃

线上零星会出现fpm进程coredump 及 fpm进程占用内存超过限制等报警告，并且两者报警的时间上往往都比较接近，如下：

时间上接近，那么出现两者报警的原因有可能是相同的，登录机器gdb调试coredump生成core文件：

cd /***/coresave/
gdb /***/php7/sbin/php-fpm -c core.php-fpm.12121.1528322653
bt
#0  0x0000003f0f089770 in memcpy () from /lib64/libc.so.6
#1  0x00000000006403c5 in zend_string_init (stmt=0x7f505b478380, colno=)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_string.h:159
#2  pdo_mysql_stmt_describe (stmt=0x7f505b478380, colno=)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/ext/pdo_mysql/mysql_statement.c:705
#3  0x000000000063a795 in pdo_stmt_describe_columns (stmt=0x7f505b478380) at /**/**/offcial_code/php/7.0.6/php-7.0.6/ext/pdo/pdo_stmt.c:206
#4  0x000000000063add5 in zim_PDOStatement_execute (execute_data=, return_value=0x7f505b4157e0)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/ext/pdo/pdo_stmt.c:523
#5  0x00007f5054056bf1 in hp_execute_internal (execute_data=0x7f505b415830, return_value=0x7f505b4157e0) at /**/**/xhprof/extension/xhprof.c:1775
#6  0x0000000000879702 in ZEND_DO_FCALL_SPEC_HANDLER (execute_data=0x7f505b415680)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:844
#7  0x0000000000841a40 in execute_ex (ex=) at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:417
#8  0x00007f50540583d1 in hp_execute_ex (execute_data=0x7f505b415680) at /**/**/xhprof/extension/xhprof.c:1748
#9  0x000000000087957a in ZEND_DO_FCALL_SPEC_HANDLER (execute_data=0x7f505b4155a0)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:800
#10 0x0000000000841a40 in execute_ex (ex=) at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:417
#11 0x00007f50540583d1 in hp_execute_ex (execute_data=0x7f505b4155a0) at /**/**/xhprof/extension/xhprof.c:1748
#12 0x000000000087957a in ZEND_DO_FCALL_SPEC_HANDLER (execute_data=0x7f505b4154a0)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:800
#13 0x0000000000841a40 in execute_ex (ex=) at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:417
#14 0x00007f50540583d1 in hp_execute_ex (execute_data=0x7f505b4154a0) at /**/**/xhprof/extension/xhprof.c:1748
#15 0x000000000087957a in ZEND_DO_FCALL_SPEC_HANDLER (execute_data=0x7f505b4153b0)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:800
#16 0x0000000000841a40 in execute_ex (ex=) at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:417
#17 0x00007f50540583d1 in hp_execute_ex (execute_data=0x7f505b4153b0) at /**/**/xhprof/extension/xhprof.c:1748
#18 0x00000000007f52a8 in zend_call_function (fci=0x7ffebd295f40, fci_cache=0x7ffebd295f90)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_execute_API.c:866
#19 0x0000000000709fef in zif_call_user_func_array (execute_data=0x7f505b415330, return_value=0x7f505b415300)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/ext/standard/basic_functions.c:4811
#20 0x00007f5054056bf1 in hp_execute_internal (execute_data=0x7f505b415330, return_value=0x7f505b415300) at /**/**/xhprof/extension/xhprof.c:1775
#21 0x0000000000879702 in ZEND_DO_FCALL_SPEC_HANDLER (execute_data=0x7f505b415290)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:844
#22 0x0000000000841a40 in execute_ex (ex=) at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:417
---Type  to continue, or q  to quit---
#23 0x00007f50540583d1 in hp_execute_ex (execute_data=0x7f505b415290) at /**/**/xhprof/extension/xhprof.c:1748
#24 0x000000000087957a in ZEND_DO_FCALL_SPEC_HANDLER (execute_data=0x7f505b4150f0)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:800
#25 0x0000000000841a40 in execute_ex (ex=) at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:417
#26 0x00007f50540583d1 in hp_execute_ex (execute_data=0x7f505b4150f0) at /**/**/xhprof/extension/xhprof.c:1748
#27 0x0000000000887037 in ZEND_INCLUDE_OR_EVAL_SPEC_TMPVAR_HANDLER (execute_data=0x7f505b415030)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:40848
#28 0x0000000000841a40 in execute_ex (ex=) at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:417
#29 0x00007f50540583d1 in hp_execute_ex (execute_data=0x7f505b415030) at /**/**/xhprof/extension/xhprof.c:1748
#30 0x000000000089496b in zend_execute (op_array=0x7f505b46a000, return_value=)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend_vm_execute.h:458
#31 0x0000000000802233 in zend_execute_scripts (type=8, retval=0x0, file_count=3) at /**/**/offcial_code/php/7.0.6/php-7.0.6/Zend/zend.c:1427
#32 0x00000000007a4b40 in php_execute_script (primary_file=0x7ffebd298990) at /**/**/offcial_code/php/7.0.6/php-7.0.6/main/main.c:2494
#33 0x00000000008a27fe in main (argc=, argv=)
    at /**/**/offcial_code/php/7.0.6/php-7.0.6/sapi/fpm/fpm/fpm_main.c:1968

可以看到是在调用pdo扩展读取MySQL数据后，然后copy读取到的数据（memcpy）时出现的coredump

通过php的gdb工具.gdbint，来查看对应的zbacktrace

source /tmp/php-src-PHP-7.0.6/.gdbinit
zbacktrace
[0x7f505b415830] PDOStatement->execute(array(1)[0x7f505b415890]) [internal function]
[0x7f505b415680] ******Mysql->run("SELECT40*40FROM40table_name40WHERE4040user_id40=40?", array(1)[0x7f505b4156f0], "select") /**/**/**/**/helper/mysql.php:270
[0x7f505b4155a0] ******Mysql->select("table_name", "40user_id40=40?40", array(1)[0x7f505b415620]) /**/**/**/**/helper/mysql.php:364
[0x7f505b4154a0] ******ModelUserFaceAuth->getInfoByUidForApi("144796772") /**/**/**/**/model/user/faceauth.php:200
[0x7f505b4153b0] ******ControllerUserFaceAuthInfo->index(array(2)[0x7f505b415410]) /**/**/***/***/controller/user/faceauthinfo.php:50
[0x7f505b415330] call_user_func_array(array(2)[0x7f505b415390], array(1)[0x7f505b4153a0]) [internal function]
[0x7f505b415290] ***FrameworkBaseRouter->run(array(2)[0x7f505b4152f0]) /**/**/**/**/base/router.php:96
[0x7f505b4150f0] (main) /**/**/**/**/framework.php:139
[0x7f505b415030] (main) /**/**/***/***/index.php:46

是在执行“SELECT40*40FROM40table_name40WHERE4040user_id40=40? ”出现的问题

此时两种可能，第一个传入的参数是否有问题？第二个是此语句返回的数据是否有问题？

先验证传入参数：

继续看当时传入的参数是什么？打印地址 0x7f505b415620 当时的值

(gdb) print ((zval *)0x7f505b415620)
$1 = (zval *) 0x7f505b415620
(gdb) p $1
$2 = (zval *) 0x7f505b415620
(gdb) p *$1
$3 = {value = {lval = 139983105408624, dval = 6.9160843380575109e-310, counted = 0x7f505b45be70, str = 0x7f505b45be70, arr = 0x7f505b45be70,
    obj = 0x7f505b45be70, res = 0x7f505b45be70, ref = 0x7f505b45be70, ast = 0x7f505b45be70, zv = 0x7f505b45be70, ptr = 0x7f505b45be70, ce = 0x7f505b45be70,
    func = 0x7f505b45be70, ww = {w1 = 1531297392, w2 = 32592}}, u1 = {v = {type = 7 "a", type_flags = 28 "34", const_flags = 0 "00",
      reserved = 0 "00"}, type_info = 7175}, u2 = {var_flags = 0, next = 0, cache_slot = 0, lineno = 0, num_args = 0, fe_pos = 0, fe_iter_idx = 0}}
 //此时的参数传入的是个数组 type=7；继续查看数组内容是啥；,
(gdb) p *$1.value.arr.arData.key
Cannot access memory at address 0x0 //key为空
p *$1.value.arr.arData.val.value.str.val@30
$10 = "1447967720000003773773773770100000006000000H24252+0"
//传入参数user_id=144796772,入参没问题

那当时语句返回的数据呢？

根据前面查看core文件的信息可以知道，返回数据后，最终调用了pdo_mysql_stmt_describe 函数，也正是在这之后出现的coredump，此函数中变量stmt 存储着sql语句执行后的返回值。
继续看返回stmt里面值是什么？//pdo_mysql_stmt_describe (stmt=0x7f505b478380, colno=) （注：打印某个地址的值时，需要知道变量的类型，
对应的数据结构也需在源码中看，否则无法继续跟进，此处查看stmt 变量的类型为pdo_stmt_t ）
先记住几个变量：

(gdb) print ((pdo_stmt_t *)0x7f505b478380)
$24 = (pdo_stmt_t *) 0x7f505b478380 //stmt变量对应的是$24
(gdb) p (pdo_mysql_stmt *)$24.driver_data
$31 = (pdo_mysql_stmt *) 0x7f505b45a500
(gdb) p (struct pdo_column_data *) $24.columns
$41 = (struct pdo_column_data *) 0x7f505b4b5300
 
pdo_mysql_stmt_describe函数的php的源码如下 ：
static int pdo_mysql_stmt_describe(pdo_stmt_t *stmt, int colno) /* {{{ */
{
    pdo_mysql_stmt *S = (pdo_mysql_stmt*)stmt->driver_data;//变量$31
    struct pdo_column_data *cols = stmt->columns;//$变量$41
    int i;
 
    PDO_DBG_ENTER("pdo_mysql_stmt_describe");
    PDO_DBG_INF_FMT("stmt=%p", S->stmt);
    if (!S->result) {
        PDO_DBG_RETURN(0);
    }
 
    if (colno >= stmt->column_count) {
        /* error invalid column */
        PDO_DBG_RETURN(0);
    }
 
    /* fetch all on demand, this seems easiest
    ** if we"ve been here before bail out
    */
    if (cols[0].name) {
        PDO_DBG_RETURN(1);
    }
    for (i = 0; i < stmt->column_count; i++) {
    //stmt->column_count的值是17，对应的是table_name表中列的总数
 
        if (S->H->fetch_table_names) {
            cols[i].name = strpprintf(0, "%s.%s", S->fields[i].table, S->fields[i].name);
        } else {
            cols[i].name = zend_string_init(S->fields[i].name, S->fields[i].name_length, 0);
//猜想：1、coredump是在调用zend_string_init函数里面的memcpy ()，猜想越界访问受保护的内存？
//2、内存占用超出PHP限制大小是否也是在这出的问题呢，调用zend_string_init时传入的S->fields[i].name_length 过大导致？
 
        cols[i].precision = S->fields[i].decimals;
        cols[i].maxlen = S->fields[i].length;
 
#ifdef PDO_USE_MYSQLND
        if (S->stmt) {
            cols[i].param_type = PDO_PARAM_ZVAL;
        } else
#endif
        {
            cols[i].param_type = PDO_PARAM_STR;
        }
    }
    PDO_DBG_RETURN(1);
}

猜想：1、coredump是在调用zend_string_init函数里面的memcpy ()，猜想越界访问受保护的内存？2、内存占用超出PHP限制大小是否也是在这出的问题呢，调用zend_string_init时传入的S->fields[i].name_length 过大导致？继续 打印验证；

打印当时返回的数据来验证前面的猜想：

//先看一下S->fields[i] 变量的值
(gdb) p $31.fields[0]
$79 = {sname = 0x7f505b45fdc0, name = 0x7f505b45fdd8 "id", org_name = 0x7f505b403a17 "id", table = 0x7f505b403a03 "table_name",
  org_table = 0x7f505b403a0d "table_name", db = 0x7f505b4039f4 "db_name", catalog = 0x7f505b4039f0 "def", def = 0x0, length = 20, max_length = 0,
  name_length = 2, org_name_length = 2, table_length = 9, org_table_length = 9, db_length = 14, catalog_length = 3, def_length = 0, flags = 49699,
  decimals = 0, charsetnr = 63, type = MYSQL_TYPE_LONGLONG, root = 0x7f505b4039f0 "def", root_len = 45}
//name=“id”,table="table_name",很明显是数据表中某一列的信息信息数据，pdo_mysql_stmt_describe函数的作用是变量S->fields 并赋值给变量cols；
//继续打印：
(gdb) p $31.fields[0].name_length
$64 = 2
(gdb) p $31.fields[1].name_length
$65 = 7
(gdb) p $31.fields[2].name_length
$66 = 10
(gdb) p $31.fields[3].name_length
$67 = 13
(gdb) p $31.fields[4].name_length
$68 = 16
(gdb) p $31.fields[13].name_length
$69 = 5
(gdb) p $31.fields[14].name_length
$70 = 8
(gdb) p $31.fields[15].name_length
$71 = 0
(gdb) p $31.fields[16].name_length
$72 = 5863687//此时罪魁祸首出现了，读取的p $31.fields[16].name_length 出现了一个巨大的值；
(gdb) p $31.fields[16]//打印变量看，出现了访问越界
$109 = {sname = 0x7f505b464028, name = 0xffffffff00001406 
,//访问越界
  org_name = 0x800000000b88b287 
, table = 0x7f505b45d0c0 "Asia/Shanghai",
  org_table = 0x7f505b45d120 "20321E[P177", db = 0xffffffff00001406 
,
  catalog = 0x80000652f67b748b 
, def = 0x7f505b45d140 "0j03IP177", length = 139983105413536,
  max_length = 8589939718, name_length = 5863687, org_name_length = 2147483648, table_length = 1531302336, org_table_length = 32592, db_length = 1531302432,
  catalog_length = 32592, def_length = 5126, flags = 3, decimals = 1929407563, charsetnr = 2147537079, type = 1531302464,
  root = 0x7f505b464078 "300MF[P177", root_len = 18446744069414589446}

stmt->driver_data->fields数组实际的大小与 stmt->column_count标记大小不一致，导致了在循环该数组时，出现内存访问越界，如果此时访问的内存受系统保护则coredump,否则也取到一个很大的值，初始化一个极大的字符串，导致内存占用超出PHP限制的大小；

为什么stmt->driver_data->fields数组与 stmt->column_count标记的大小不一致呢？往前追溯stmt变量的初始化，看是否存在问题？

在PHP源码中函数 pdo_mysql_stmt_execute->pdo_mysql_stmt_execute_prepared_mysqlnd，对column_count 及fields 有做定义，具体如下：

static int pdo_mysql_stmt_execute_prepared_mysqlnd(pdo_stmt_t *stmt) /* {{{ */
{
    pdo_mysql_stmt *S = stmt->driver_data;
    pdo_mysql_db_handle *H = S->H;
    int i;

    PDO_DBG_ENTER("pdo_mysql_stmt_execute_prepared_mysqlnd");

    if (mysql_stmt_execute(S->stmt)) {//mysqlnd/mysqlnd_ps.c 619
        pdo_mysql_error_stmt(stmt);
        PDO_DBG_RETURN(0);
    }

    if (S->result) {
        /* TODO: add a test to check if we really have zvals here... */
        mysql_free_result(S->result);
        S->result = NULL;
    }

    /* for SHOW/DESCRIBE and others the column/field count is not available before execute */
    stmt->column_count = mysql_stmt_field_count(S->stmt);
    for (i = 0; i < stmt->column_count; i++) {
        mysqlnd_stmt_bind_one_result(S->stmt, i);
    }

    S->result = mysqlnd_stmt_result_metadata(S->stmt);
    if (S->result) {
        S->fields = mysql_fetch_fields(S->result);
        /* if buffered, pre-fetch all the data */
        if (H->buffered) {
            if (mysql_stmt_store_result(S->stmt)) {
                PDO_DBG_RETURN(0);
            }
        }
    }

    pdo_mysql_stmt_set_row_count(stmt);
    PDO_DBG_RETURN(1);
}
定义代码：
stmt->column_count = mysql_stmt_field_count(S->stmt);//返回17 
S->fields = S->fields = mysql_fetch_fields(S->result);//实际数组则只有15

问题的根源就是 宏mysql_stmt_field_count（获取数组大小） 与 宏mysql_fetch_fields（获取数组内容） 返回对应不上导致的；

这两个宏定义如下：

mysql_stmt_field_count：
#define mysql_stmt_field_count(s)       mysqlnd_stmt_field_count((s))
#define mysqlnd_stmt_field_count(stmt)      (stmt)->m->get_field_count((stmt))//函数指针 php_mysqlnd_stmt_field_count_pub 函数
mysql_fetch_fields：
#define mysql_fetch_fields(r) mysqlnd_fetch_fields((r))//函数指针：
#define mysqlnd_fetch_fields(result) (result)->m.fetch_fields((result)) //函数指针 php_mysqlnd_res_fetch_fields_pub 函数

看这两个函数实现，函数实现：

stmt->column_count：php_mysqlnd_stmt_field_count_pub函数->最终取的是 stmt->driver_data.stmt,data.field_count；

stmt->driver_data->fields数组：php_mysqlnd_res_fetch_fields_pub函数->php_mysqlnd_res_meta_fetch_field_pub函数，最终取的是：stmt->driver_data.result.meta.fields 此数组的长度与 stmt->driver_data.stmt.data.field_count 取得值存在误差；

继续跟进为什么两者存在偏差？

猜测原因：猜测原因：stmt->driver_data.result.meta.fields 此数组的长度与 stmt->driver_data.stmt.data.field_count是两次链接读取的；

先看select函数的核心实现：

$t1 = microtime(true);
$pdoStmt = $this->pdo->prepare($sql); //调用的是 php_mysqlnd_stmt_prepare_pub
$prepareSuccess = true;
$return = true;
$result = $pdoStmt->execute($bind);//调用的是  php_mysqlnd_stmt_execute_pub
gdb调试，依次打上断点：
b php_mysqlnd_stmt_prepare_pub
b php_mysqlnd_stmt_execute_pub

在 php_mysqlnd_stmt_execute_pub 函数可以看到 该变量（ stmt->driver_data.stmt.data.field_count ）已经被初始化（在php_mysqlnd_stmt_prepare_pub初始化），而stmt->driver_data.result.meta.fields 的初始化则是在之后的php_mysqlnd_res_read_result_metadata_pub函数中赋值，这就导致了两者之间可能不一致的情况；

php_mysqlnd_res_read_result_metadata_pub函数具体bt信息如下：

#0  php_mysqlnd_res_read_result_metadata_pub (result=0x7ffff61e8040, conn=0x7ffff61b0400)
    at /**/offcial_code/php/7.0.6/php-7.0.6/ext/mysqlnd/mysqlnd_result.c:357
#1  0x0000000000798971 in mysqlnd_query_read_result_set_header (conn=0x7ffff61b0400, s=)
    at /**/offcial_code/php/7.0.6/php-7.0.6/ext/mysqlnd/mysqlnd_result.c:533
#2  0x000000000079eb71 in mysqlnd_stmt_execute_parse_response (s=0x7ffff61f0000, type=)
    at /**/offcial_code/php/7.0.6/php-7.0.6/ext/mysqlnd/mysqlnd_ps.c:504
#3  0x000000000079bc6c in php_mysqlnd_stmt_execute_pub (s=0x7ffff61f0000) at /**/offcial_code/php/7.0.6/php-7.0.6/ext/mysqlnd/mysqlnd_ps.c:614

验证一下此处的stmt变量是否为php_mysqlnd_stmt_prepare_pub函数中使用的变量，打印两个变量地址对比结果如下：

php_mysqlnd_stmt_prepare_pub 时的 stmt 地址 ： $38 = (MYSQLND_STMT_DATA *) 0x7fffed40a700
php_mysqlnd_stmt_execute_pub 时的 S->stmt.data 的stmt地址 ： $46 = (MYSQLND_STMT_DATA *) 0x7fffed40a700

继续跟进代码，php_mysqlnd_stmt_execute_pub函数的整体的调用流程如下：

第一步：
if(!stmt){}else{//stmt 为第一次链接mysql,调用（php_mysqlnd_stmt_prepare_pub）执行返回的数据
    result = stmt.result //result第一次函数调用返回的结果，里面包含了表的列数信息等 mysqlnd_result.c:525行
}
第二步：
//初始化result->meta，传入列数为result->field_count，即第一次调用mysql返回的列数，问题的关键点在这，此处应该取 rset_header->field_count 就不会出问题；
result->meta = result->m.result_meta_init(result->field_count, result->persistent); //mysqlnd_result.c 371行 
第三步：
//rset_header变量的初始化为mysqlnd_result.c:413行 
conn->field_count = rset_header->field_count;//rset_header 为第二次链接mysql读取到的返回值，（此阶段为php_mysqlnd_stmt_execute_pub函数中） mysqlnd_result.c:499行
第四步：
stmt->field_count = stmt->result->field_count = conn->field_count;//把第二次链接mysql读取到的列数赋值给stmt->field_count  //mysqlnd_ps.c:541行
第五步：
stmt->column_count = mysql_stmt_field_count(S->stmt)；//return stmt? stmt->field_count : 0;//把stmt->driver_data.stmt.field_count(即第四步的变量stmt->field_count) 赋值给 stmt->column_count //mysql_statement.c:293行
第六步：
S->fields = mysql_fetch_fields(S->result);//把stmt->driver_data.result.meta.fields 赋值给 stmt->driver_data.fields //mysql_statement.c:300行 
第七步：
调用 pdo_mysql_stmt_describe函数 执行如下代码，如果两次读数据库返回的field_count不一致,则可能造成coredump及内存超出限制大小
for (i = 0; i < stmt->column_count; i++) {
    cols[i].name = zend_string_init(S->fields[i].name, S->fields[i].name_length, 0);
     cols[i].precision = S->fields[i].decimals;                                                                                       │
     cols[i].maxlen = S->fields[i].length;    
}

猜测的原因为：在更改表结构时，因为存在一主多从，表结构从15列改为了17列，第一次php_mysqlnd_stmt_prepare_pub预执行时读取到的从库 A的表信息，此时恰好表结构并未更改过来，列数为15，并把15存储在了 stmt.driver_data.stmt.data.result.field_count 变量中，第二次php_mysqlnd_stmt_execute_pub函数读取到从库B的表信息，次数表结构已更改为17列，取到的列数数为17，但是数组内容的初始化用的为第一次取到的列数15，即上文第二步执行的过程；之后遍历循环数组内容时用的列数为第二次返回的列数17，因此这时出现了内存越界访问，也就是造成前文的报警；

建议

1、作者在遍历循环数组内容（stmt->driver_data->fields）时 不应该取 stmt->column_count 值，而应该取stmt->driver_data.result.meta.field_count更合适，其 与 stmt->driver_data.result.meta.fields（数组内容） 在同一个结构体中，且同时被初始化，不被其他逻辑污染；

2、作者在初始化列数组内容时（result->m.result_meta_init(result->field_count, result->persistent); //mysqlnd_result.c 371行 ）不应该用第一次链接MySQL返回的列数，而应该用第二次链接MySQL取到的列数，即rset_header->field_count ；

gdb断点处：

b php_mysqlnd_stmt_prepare_pub
b pdo_stmt.c:511
b mysqlnd_ps.c:540
b php_mysqlnd_stmt_execute_pub
b mysqlnd_stmt_execute_parse_response
b mysqlnd_result_meta_init

这次问题跟进颇为不易，pdo所有的数据结构比较多且杂，代码上命名又写成一致，让人有点眼花缭乱，原因也只能一次又一次的否认重新跟进定位，大家可按照前面写的，“php_mysqlnd_stmt_execute_pub函数的整体的调用流程”中每个步骤列的代码行，逐个打上断点，gdb逐行跟进验证；

php版本为：PHP 7.0.6

粗略整理了此次跟进pdo核心所依赖的数据结构：pdo结构体梳理