深入理解PHP传参原理(PHP5.2)

首先说下今天想到的一个问题。在编写php扩展的时候，似乎参数（即传给zend_parse_parameters的变量）是不需要free的。举例：

PHP_FUNCTION(test)
{
    char*  str;
    int    str_len;

    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s", &str, &str_len) == FAILURE) {
        RETURN_FALSE;
    }

    php_printf(str);

    // 无需free(str)
}

运行正常：

test("Hello World"); // 打印Hello World

这里不用担心test函数会发生内存泄露，php会自动帮我们回收这些用于保存参数的变量。

那php究竟是如何做到的呢？要解释这个问题，还是得看php是怎么传递参数的。

EG(argument_stack)简介

简单来讲，在php中的EG中保存了一个专门用于存放参数的栈，名为argument_stack。每当发生函数调用的时候，php会将传入的参数压进EG(argument_stack)。一旦函数调用结束，则EG(argument_stack)被清理，并且等待下一次的函数调用。

关于EG(argument_stack)的struct结构、用途，php5.2和5.3实现有一些区别。本文主要以5.2为例，5.3+的变化后面抽空再说。

aaarticlea/png;base64,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" alt="" />

上图是5.2中argument_stack的大概示意图，看起来简单明了。其中，栈顶和栈底固定为NULL。函数接收的参数按照从左到右的顺序，依次被压入栈。注意，最后会被额外压入一个long型的值，表示栈里的参数个数（上图中为10）。

那被压入argument_stack的参数究竟是什么呢？其实是一个个zval类型的指针。它们指向的zva有可能是CV变量，有可能是is_ref=1的变量，还有可能是一个常量数字，或者常量字符串。

EG(argument_stack)在php5.2中被具体实现为zend_ptr_stack类型:

typedef struct _zend_ptr_stack {
    int top;                       // 栈中当前元素的个数
    int max;                       // 栈中最多存放元素的个数
    void **elements;               // 栈底
    void **top_element;            // 栈顶
} zend_ptr_stack;

初始化argument_stack

初始化argument_stack的工作是发生在php处理具体的请求之前，更准确说是处于php的php_request_startup->zend_activate->init_executor过程之中。

在init_executor函数里我们发现如下2行：

zend_ptr_stack_init(&EG(argument_stack));
zend_ptr_stack_push(&EG(argument_stack), (void *) NULL);

这2行分别代表着，初始化EG(argument_stack)，紧接着压入一个NULL。由于EG是个全局变量，因此在实际调用zend_ptr_stack_init之前，EG(argument_stack)中的所有数据全部为0。

zend_ptr_stack_init实现很简单。

ZEND_API void zend_ptr_stack_init(zend_ptr_stack *stack)
{
    stack->top_element = stack->elements = (void **) emalloc(sizeof(void *)*PTR_STACK_BLOCK_SIZE);
    stack->max = PTR_STACK_BLOCK_SIZE;   // 栈的大小被初始化成64
    stack->top = ;                      // 当前元素个数为0
}

一旦argument_stack被初始化完，则立即会被压入NULL。这里无须深究，这个NULL其实没有任何的含义。

NULL入栈之后，整个argument_stack的实际内存分布如下：

aaarticlea/png;base64,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" alt="" />

参数入栈

在压入第一个NULL之后，一旦再有参数入栈，则argument_stack会发生如下动作：

stack->top++;
*(stack->top_element++) = 参数;

我们用一段简单的php代码来说明问题：

function foo( $str ){
    print_r();
}
foo("hello world");

上述代码在调用foo的时候，传入了一个字符串常量。因此，实际上被压入栈的是一个指向存储“hello world”的zval。用vld来查看编译之后的opcode：

line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
   3     0  >   NOP
   6     1      SEND_VAL                                                  OP1[  IS_CONST (458754) 'hello world' ]
         2      DO_FCALL                                      1           OP1[  IS_CONST (458752) 'foo' ]
  15     3    > RETURN                                                    OP1[  IS_CONST (0) 1 ]

SEND_VAL指令实际上做的事情就是将“hello world”压入argument_stack。

int ZEND_SEND_VAL_SPEC_CONST_HANDLER(ZEND_OPCODE_HANDLER_ARGS)
{
        ……
        zval *valptr, *value;

        value = &opline->op1.u.constant;
        ALLOC_ZVAL(valptr);
        INIT_PZVAL_COPY(valptr, value);
        if (!) {
            zval_copy_ctor(valptr);
        }

        // 入栈，valptr指向存放hello world的zval
        zend_ptr_stack_push(&EG(argument_stack), valptr);
        ……
}

入栈完成之后的argument_stack为：

aaarticlea/png;base64,iVBORw0KGgoAAAANSUhEUgAAAd4AAACKCAIAAACLlLzBAAAXVElEQVR4nO2da2/bVoKG/X/8B7TJNGgw222aXpJ+EIqFoU6d7biLVMBMPEVqDOrUbgAPzO6orbdRJ2666iDGKJXQCoNMmiKCL/IKGq1H8MCWlSAOZNUWHMeXOkHMxnWNgPvhSNThTeKdPNL74P3g0CQlkodPjg8Pz+kSAAAA+Iwur78AAAAAOVAzAAD4DqgZAAB8B9QMAAC+A2oGAADf4a2aE8GurmDC069giaWh7q7uoSWvvwYAoN2Amq0ANQMAHIFVNdsoRQu7gpoBAI4ANUPNAADfYUTNS0PdXQ3qSqKXippdGuruCiYav6L8mwg21m6pZvl+uoeW1L4HWa225+aul35d1UNqfEOpd6nltc+g1ZwItvxsAADQh6lacyJYl9bSUHfDR5SoiPJoa5GV6PVrWmypZqkJqR01vCn9uBb7k6+m2JX4j8Zxyo40EWwcfvfQknRNAACwigk1UxqSmy4R7JI5S7pcZf3WalbdQKlmXWZcGupWOLTJxuLxaKxElg4x/jATAOA7DKtZUj+UtgdQTQBKNXcFE/X2CenOXFUz/Z1VKvviZ6g2cii/qWqLDQAAWMWgmmV/uGsqsYmardSaG60K5tWs2ESysaTdQmeteQntGQAAezGkZqWBpCaTLldRs8m2ZrrNmm7Mljx1tKRm1Sq0pPWjeVuz5okAAAATGFGz9C99mWGlS7XULEh7aMgbOBQ0GnMV7Qb1/dR7aOhSM30IjQ3oXVHH0z2UoJ4JtuqhgaozAMA2fD6GBjoOAwA6EagZAAB8h1LNsmYL+d/wDtDkE82p2f1DYJLoV5lAiENYycXxb70uMsA9fF5rBg7iuWsQo/G6yAD3gJo7F3K3nxqeRPwfqLnTgJo7F6iZoUDNnQbU3LlAzQwFau40oObOBWpmKFBzpwE1dy5QM0OBmjuNhprRlcpimOvbBDUzFKi502io2XO1tUE8vJAmgJoZCosFDFhBrmbPiyCj8fOdk55fH00WyxuPZctxxRmKnwsYcAKouf3vHH7/cGKqHByZvhhfoAWNK85Q/FzAgBNAzZ1y5ygFjSvOUPxfwIC9QM2ddefQgsYVZyisFDBgF1Bzx905i5XdWPpecGQaV5yhMFTAgC1AzZ1y58wsbowmi6c/mByIFcgPuOIMxf8FDNgL1Nzmd87B4dNUbrWHy/SPz6Xn1/n9w/T8eg+XScxWcMUZim8LGHAIY2oOz/BCqehlGU1uil94bSbv+Q3j8zvnxly1h8uIz/129w4Gr873j89Vt3kB/xkzFX8WMOAcbKm5mBU2OfJzclMQ+HjU+3vGn3cOv384miyGo3mxt5xYWRbXgZoZit8KGHAa/WrOx7cam9VrrPTCujSH8/EtPh4tZmvLHRJoMSsI2aT394wP75w71Ue9kez4zbsHh0/JktFkUawsi0DNDMVXBQy4gJVacz6+JYj/5EqCsLUSFpfXTR2e4evLpaGaJmqorqaV6Moaas1qJGYrwZHpwvIOvfBO9ZFyTaiZofingAF3sKDm6Mpao6ZMuzIf36Lqs844lCsJHrd6+/LOGU0WB2KF3b0DPStDzQzFJwUMuIYFNSc3BVrNw8Wsqpoby22LZk28s++cSKo0eHVebMRoCdTMUPxQwICbeFdrNtugEZ7hpf8l+CKe3zlGvSxAzUzF8wIGXMa4mhsCLWapHmxabc3Uchti797a5s4Zv3nXqJcFDAPLYBwqP8CHGH3lpNbvom5ksRsGbcx8fEvIzqys1X5hXw03Ku5T+aGdq+aJqXI4muf3D41u6LloEKNxovwAf+LE24CytuaOiFd3Tnp+vW8sZ8LLAho0mArU3GlAzQzfObt7Bz1cRtZbWT9QM0OBmjsNqJnhO2cgVqDf7jMK1MxQoOZOA8MbsXrnpHKrA7GClT3gijMUqLnTgJqZvHOq23xwZPrBwydWdoIrzlCg5k4DM2oz+QCdjPBpcScOq1nWrkVGVvHecYwGau40oGb21Jy7vRmO5q3vxy015+NbgrC1Ei/x8Rl/jRfIUKDmTgMNGuzdOeFoPndb8S6lcVytNZM+6X4a9oStQM2dBtTM2J1jV5VZ0HPFJe/48PGobFSpfHyr/vIRtWZdx6g1M1nAfMDSUHdX99CS11/DY6Bmxu6cwavzqdyqLbvSf8UbL+jTY1o1RkeRTXFAfkZbM5MFzAdAzYIANbN155Q3HvdwGaNjZWih+4rTYwc2ZjBQH/9Pa5QrxHIBe+atywOxwsRUOTFbUR2Au12AmgUBarbxznFBzRfjC3ZVmQXdV1w2NHb9n1LzSsYRhJodKWBHej9erOymcqsTU+W+sVxvJJvKrZp7R9/fQM2CADXbeOc4rWZ+//D0B5N2VZkFnVdcPip3fTBYekhYetxX1JrdKmCF5Z3RZPH0B5NW3gh1hKWh7q4G3UNLiWCXxLWJYFdXMFH/qbEetT3UDDU7defYzszixsX4go071HHFVSdgzMe3hLUt9UkVwjM8as1uFrDdvYP+8Tn9U9u4iqhkiZtF8y4NdYsL6TWgZkFgQs3hGXH4Hvo5EhkV2i9PllxQcyRVujFXtXGHra+4dLoD0bPkitDa5Ur1lUqbGpPdIA4WsMRspYfLyCaE9BoN22qINxGEmiX4Xc1ac02FZ3hhi/fPzK0uqLmHy1h8M1uGP684opqWBYw8IvaPnWWNGHRVuUtSV+5SNGlAzYJgUM2k/5M4fP4mV6u6CpLaq6KLq2TKqOSmkfHvteYVLGYFPp700aTaTqu5vPG4byxn7z6hZoaip4D5yM7y1mXRt0tD3bVmZtIkXfsZtWYFRtUs0L1Whbp8qXmhNLu4CqWiSttl8xkCoytrAr+2Vf9VvXEzPMOvzeQdmqvbuTvHChNT5fGbd+3dJ9TMUHQWMH/YWSnm2tLuYFA0s8TAS0PdqDVLMaxmSYOj5uzak6eGVR7cr20ZfFU3Sb88Vte62Degk9Q8ECssVnbt3SfUzFD0F7A71Ue2t30ZQ9pMIakY0/+ku3J0DyUazwShZkFwRM0qXVwnT9WeFBk0qdT4pEctV6JfDu4UNZ+8kLax2xwBamYohgqY9bG8gefYrWb1Lq61FbIlRa1ZR4NGXb5kxIaVrHyDxqzerNw5RiETTdm+W3Oj6yEeRv/FJe8N2l5mgGvYreYWXVxV+8m2+ETNOnLH1JrLG4/tGtKIxnPRIEaj/+Lu7h0ER6Yd6uz8/f0frn33j9HYrbMj1xD9Gbx0/fNvssvf6xo20v4GDWUXV0kHONVW6SZRGdKs49RcWN5x4u9THVcc8UtMFLDxm3dtf3T894WV185f8fy/KNbzYvjSN5P/bH6q/d6vmZU4qub0/HokVWq9nkFwxRmKiQJmb8V578ef3v04Rb7GkV/98dmzV55/J/nCwF9fGvzW85Pj/7zy/q0XBv564vzXx8Oxo72fkNP42vkr97c1h6mCmu2Jo2qemCrH0vds3y2uOEMxV8DsqjjvPOJff+/LQIg78sZHz537i+dng/WcOP81EfRzb32i1b4BNdsTR9X86fU7Ng44J4IrzlDMFTBScbbYt2fvx5+Il4+eGUMd2a688v6tY32fETt/f/8H5WmHmu2Jo2oeTRZnFjds3y2uOEMxXcAGYgWLb6D89sMk8fIr79/y/Dy0VYbSx976UyDEvXru8sHP8sFdMW2rnbFyAzTB+vsmqqP6Qs0MxXQBS+VWP71+x3TJyRSWAyHuyBsfob7sRF55/9bRM2OBEHftu3/IzjzUzICaeyNZKy93FZZ3erjMxFRZ9oct1MxQTBewBw+f9EaULwPohfTHQPuyczlx/utAiDsZvrT340/0mUeDhj1xVM3WR9B/8PDJaLLYw2XoYUX1XHHSFVI6xZ/4jg/9c+O39LStyt/64f0gFmOlgPWN5cz91168tx4IcUd7P/H88Ns7pFnjb7NF+uRDzfbEOTXz+4fBkWlbdlXeeDwQK/RGsrnbm4LunuxrW9TAgVAzgwVs8Oq8uQaxz7/JBkLc8be/8Pzw2zv/1n8tEOLe/ThFn3yo2Z44p+bqNm/vcKCF5Z1wNN8/PvdMX1SXmmeKGjqGmtkoYJFUydxjZNKR+cT5rz0//PbOS+/dCIS4185foU8+1GxPnFPzYmVX/6uAB4dPFyu7i5Xd3O3NiamymEiqNBAr0Dl5IX3yQvpff5dselx1mTaGAISa2StgE1Nlc50vSZ+5F39/3fPDb/sEQtyxMxH65EPNtp1Zh9Scyq0q3xrg9w8XK7vp+fWJqfLg1XnSTHHyQrpvLEfMG0mVaDWn59eJsknGb949eSH9y/6vjrzxUdPjasiUnkgbamargN2Yq5p7ZenVc5cDIc69PnNkVAYDU20Y2ZWNO3cg5A0U+uRDzfbEOTUPXp0nTcPVbT4xW7kYX+jhMr2R7ECsMH7z7sRUmdhW53PC3b2DwavzfWO5wvKO3rZmyfBSUDN7BaywvGPuRX+iZvcOE2qmsEXNmKDTKTUfHD4NjkxXd/j+8bkeLjN+827u9qbpURESs5XgyLTYi86Ymmtz2WxmZUsko7zSIwtCzX4pYOTxr4kNoWbX0lZqlgx953UcUnNheec3l/+vN5K1OJf2neoj0tZR3RanJzesZmJegR4gO7kpyGbabhR9qNkvBWx378Dck2So2bVAzU7FXjU/ePhkZnEjlr732h9m/n00Y/EtbTKQQnp+XbbcuJrJGNxSvdKTIUjKvTilL6HWGCJd4v2FYyUWC5i5/pdQs2uxruZi472ihhZpNWutoGMqbr3bTspue2IKYg1qHVdj7s6pbvOkpZg8rLsYX+gfnyNP8yKpUiq3Gvrwf+l6rr3g6QJDsajmvrFceeOx0a08VHNj2Het/8KpkdwF5VRH+tUs3Y8n9jhlWc10HUreqphNtlih1VTcurel5tVuGFycy9WjBELcL359ie4U0aTvWnBkmvRdI40MF+MLE1PlxGxlsbJLi7i88djKK7YtgZoZikU1x9L3TMxH5ZGa+TX5F5HbmaqHUTQXsZqa1fdjbCYme2JNzVL9UWasq7nlCvLlskkF9W1bP7kKNXv5KDIQ4o7+x39rqVnWd011sCElkVTJ9lkqaKBmhmJRzYuV3f7xOaNbeaNmQRCkM4IKgvRpc201uiomqfA11tEja6k36rV1t+t51tSsnGJVZs+WKwxPnmo2qWDrbU8lN9XVTJ1oTx402f4Y0NG53QhQM0OxXsBMFCeP1CytIxMzUErlSop1xG2ldbXmaiYWVuhCYXlXYmetWXYwylqzygrDk6f01Zq1tm2mZuoCuF99tl3NTkzsJgNqZijWC9hosmi0RPniMaB8oexhshRxtdZqJvtRachWedbtfCy2NRez6t9YMmF20xXqR64y36uubeVqVnneWsx68ejfXjXv7h2c/mDSykCgegh4PYYqYjRWLnd54/HpDyYNVZx9oWbSO8B+NZOeBWrVQVJPd7f3l609NATJW2EqPTTUV9CcilvPtrSaJd1sqfaQNmjQSOVWL8YX7NqbFm8OT3juGkR/Xj132eIVvxhfMFRx9rGaW1W/OqzWjGiGnD2Ldw7h4PBpD5cx0dUJgOYYrTj7Us3KMcT17aqd25oR7dio5lj63miy2Ho9AIwzfvOu/tLlTzWLfyJL7Un3uNXXQ0NtP7UeGq6/mQI1OxW71Hyn+qiHy+jsXQeAUQ4On4ajeeWroar4VM2SF1IkGFOz5n48eFgFNTsVW9R8cPi0N5K1OP8xAM2pbvPBkWk9D5l9q+ZTw8rutlKf6n8bULYfj97khpqdii1qjqRKViY/BkAnN+aq4Wi+5R9nbqu5g9NazYiVWLlbCss7vZGsxelZAdDJxFSZtnNitqIse1Az1NwmMX2fPHj4pIfL3Kk+Mr0HAIxC23k0Wewby8nG0oKafaRmz78io7Gi5gcPn/RGsjqfzABgIxNT5b6xHKkTpHKrPVyGTKlDgJpdC9TsVEyrmd8/DEfzFkfKB8A0heWdHi5DJg8kHYTE11KgZtcCNTsVc2omXjYxWiMANkJmjCSd6h48fNI/PjcQK/D7h1Cza4GanYoJNcPLwFfkbm8OXp0PjkyP37xL5qI89c6XcII7gZqdilE1V7d5eBn4kOo2/+n1O31juZMX0i9euPWLX1/y/ObqhEDNTsWQmtPz66qT9QHgOYXlndFkMTgy/en1O6d/9z9wgjthS83ezAZrLjrVzO8fkgkAnZvxDwAT8PuHqdxqbyRLWpxJH2e0NbsWq2p2dxJrD9Rs+gD1qHmxskseheO9EuAfdvcOIqlScGQ6kirJetZDza4Fam4Rh9S8WNkdiBUwPgbwIdVtPpVbVX1pG2p2LVbULJlcgB7nvo44In4+vsXHo+K4+HqGcaIG0W+YUWOEfskK9Adtco3vQ3+oclvlhloHqDeqaub3D2/MVfvH5/BGCWARqNm12Ftrzse3GqLkSuKgTcRxNVNrTBNFJx/fElVID7oqqrnZCjKxkl/JvoxiW8WG9aOwUms+0vsxmTC7sLwzMVUeiBWCI9OjySJqyoBR2lbNWqPQmVvNjtiqZtlEq9GVtVpdVdoQ0Vje5Pgb+6E+Qn02WJUVlN9NYzbY+jqKDZtPBasjgRD3TN+fBmKFgVjhYnwhMVtZrOyiTRkwDdTMppol0/pNUvOlytqIW82jKh93VZCbt+UKTb6b+rYGZ+nWEYvDGwHgQ6BmNtXsTK2ZinqtWWUF5XfTqDWrbgg1A6AK1MyUmqUTWouPy7TamqnlWpHsh4oo0JYr1L+bSo1eddumajZ1JaBm0H5AzcyoWeztQD9YqyGdRTw7s7JW+4VqhVd9t4Jk5xo9NNRXaNLYotxWU82KA9QbqBm0H26omTQ5Sv9UDc/wguIeVFkYFSVDUKgmurJGNolKdaThXPIRhMZWjKhZT1h6i8+uQM2g/XCl1kwqQxKrqk5rzZUEulMsrVEaiXmImkublME11aw1FSzUzHagZtB+uNOgQZwo7ThAULydIFqyXgumPVN3q+wBmGLhsJqa6/0FJH+FE9pdzZJWBRGj7Qa+DdQM2g931FyToKQ1UsiWNgXaD0nJP4mFVZ8hCYKsD4Kg1dBBO1d9h23XoNGJgZpB++HSY0CpAcMzvCDw8aRkobRmTRSs0u9L3h6t5Vb5co0dQs1tEKgZtB9u9dCgzZiPbxEb0h29ZO3RKs3TtcgeKraTmhErceV+AcAlXOs816jtin0q6gvrbzbIR9fpoFrzm8MTnquN6bx67rJbtwwAbuBev2ZRgqShOUktLBUbjq6vb6ytubWa/d3WDAAANC6+clJrvsiWBOkYloIg8Gtbgrz5QtGh4pRqlzvdaq7vUK1zHtQMAPAVbr4N2FAh9fpJo6+xYvgEjW7I0kYJ/WqWjglcY4tHrRkA4DtcfVG73gdZ0qqgVjtW/raGLgU3W07rXhwiAmoGAPiLmpqH0i7ZuYNz5I2PoGYAgC5ef+/LQIh7afBbz83V9lF28YKaAQDq/PbDZCDEvfBuynNztXdevvCdsosX1AwAUOfjialAiPvlb656Lq/2zvPvJAMh7uzINfrkQ80AAHX+vrASCHHPvPmp5/Jq7xx/+4tAiPv8G8k4Q1AzAECdg58Pj52JBELci7+/7rm/2jUvX/juX17/r0CI+/7+D/TJh5oBAJr8+Xq+VnFGPw1n8ux/jgdC3GjsluzMQ80AAE0Ofj58MXwpEOKePXvFc4u1X54795dAiDt2JrLzSD4zANQMAGjG8vebpFnj+NtfoO5su5cDIe5vs0XlaYeaAQAtyBSWiZ2P9X2GdmfrefnCd8+evUK8LHv6JwI1AwBaU7y3/txbnxCbHH/7i+ffSb7y/i3PHcdcTpz/+ng4Rp77HTsT+Wbyn1onHGoGAOhi78efol9lSPVZzNEzY8f6PkNa5siv/kift8FL1+9vP2pytqFmAIAB7m8/+vP1/NmRa56PkM5i3hyeiH6VkfWTUwVqBgAA3wE1AwCA74CaAQDAd/w/EN0breG6JogAAAAASUVORK5CYII=" alt="" />

参数个数

前文说到，实际上并非把所有参数入栈就完事了。php还会额外压入一个数字，表示参数的个数，这个工作并非发生在SEND_XXX指令的时候。实际上，在真正执行函数之前，php会将参数个数入栈。

继续沿用上面的例子，DO_FCALL 指令用于调用foo函数。在调用foo之前，php会自动填入argument_stack最后一块。

static int zend_do_fcall_common_helper_SPEC(ZEND_OPCODE_HANDLER_ARGS)
{
    ……
    // 在argument_stack中压入2个值
    // 一个是参数个数（即opline->extended_value）
    // 一个是标识栈顶的NULL
    zend_ptr_stack_2_push(&EG(argument_stack), (void *)(zend_uintptr_t)opline->extended_value, NULL);
    ……
    if (EX(function_state).function->type == ZEND_INTERNAL_FUNCTION) {
        ……
    }
    else if (EX(function_state).function->type == ZEND_USER_FUNCTION) {
        ……
        // 调用foo函数
        zend_execute(EG(active_op_array) TSRMLS_CC);
    }
    else { /* ZEND_OVERLOADED_FUNCTION */
        ……
    }
    ……
    // 清理argument_stack
    zend_ptr_stack_clear_multiple(TSRMLS_C);
    ……
    ZEND_VM_NEXT_OPCODE();
}

压入参数个数和NULL之后，用于foo调用的整个argument_stack已然完成。

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" alt="" />

获取参数

继续跟进上面的例子。让我们深入到foo函数，看看foo的opcode是什么样子的。

line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
   3     0  >   RECV                                                      OP1[  IS_CONST (0) 1 ]
   4     1      SEND_VAL                                                  OP1[  IS_CONST (5) 123 ]
         2      DO_FCALL                                      1           OP1[  IS_CONST (459027) 'print_r' ]
   5     3    > RETURN                                                    OP1[  IS_CONST (0) null ]

第一条指令是RECV，从字面上理解便是用于获取栈中参数的。实际上，SEND_VAL和RECV有点对应的感觉。每次函数调用之前SEND_VAL，在函数内部进行RECV。为什么不说是完全对应，实际上RECV指令并非一定需要。只有当用户定义的函数被调用是，才会产生RECV。我们编写的扩展函数，php自带的内建函数，都不会有RECV。

需要额外指出的是，每次SEND_VAL和RECV 均只能处理一个参数。也就是说如果传参的过程中有多个参数，那么会产生若干SEND_VAL以及若干RECV。这里引出一个很有趣的话题，传入参数和获取参数的顺序是怎样的呢？

答案是，SEND_VAL会将参数从左至右的进行压栈，而RECV一样的从左至右获取参数。

static int ZEND_RECV_SPEC_HANDLER(ZEND_OPCODE_HANDLER_ARGS)
{
    ……// param拿参数的顺序是沿着栈顶-->栈底
    if (zend_ptr_stack_get_arg(arg_num, (void **) &param TSRMLS_CC)==FAILURE) {
        ……
    } else {
        zend_free_op free_res;
        zval **var_ptr;

        // 验证参数
        zend_verify_arg_type((zend_function *) EG(active_op_array), arg_num, *param TSRMLS_CC);
        var_ptr = get_zval_ptr_ptr(&opline->result, EX(Ts), &free_res, BP_VAR_W);

        // 获取参数
        if (PZVAL_IS_REF(*param)) {
            zend_assign_to_variable_reference(var_ptr, param TSRMLS_CC);
        } else {
            zend_receive(var_ptr, *param TSRMLS_CC);
        }
    }

    ZEND_VM_NEXT_OPCODE();
}

zend_assign_to_variable_reference 和 zend_receive 都会完成“获取参数” 。“获取参数”不太好理解，实际它究竟是做哪些事情呢？

说到底很简单，“获取参数”就是将这个参数添加到当前函数执行期间的“符号表”中，具体对应为EG(current_execute_data)->symbol_table。本示例中，RECV完成之后，函数体内的symbol_table中有了一个符号‘str’，它的值为“hello world”。

但argument_stack并没有发生一丝变化，因为RECV仅仅是读取参数，而不会对栈产生类似pop操作。

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" alt="" />

清理argument_stack

foo内部的print_r也是一个函数调用，因此也会产生压栈-->清栈的操作。因此print_r执行之前的argument_stack为：

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" alt="" />

print_r执行之后argument_stack又回到了foo刚RECV完的状态。

具体调用print_r的过程并非本文阐述的重点。我们关心的是当调用foo结束之后，php是如何清理argument_stack的。

上面展示的do_fcall代码片段中可以看出，清理工作由zend_ptr_stack_clear_multiple完成的。

static inline void zend_ptr_stack_clear_multiple(TSRMLS_D)
{
    void **p = EG(argument_stack).top_element-;
    // 取栈顶保存的参数个数
    int delete_count = (int)(zend_uintptr_t) *p;
    EG(argument_stack).top -= (delete_count+);

    // 从上至下，依次清理
    while (--delete_count>=) {
        zval *q = *(zval **)(--p);
        *p = NULL;
        zval_ptr_dtor(&q);
    }
    EG(argument_stack).top_element = p;
}

注意这里清理栈中zval指针，使用的是zval_ptr_dtor。zval_ptr_dtor会将refcount减1，一旦refcount减为0，则保存该变量的内存区域会被真正的回收掉。

在本文示例中，foo调用完毕之后，保存“hello world”的zval状态为：

value        "hello world"
refcount     1
type         6
is_ref       0

由于refcount只剩1，因此，zval_ptr_dtor会将“hello world”真正从内存中销毁。

消栈完毕之后的argument_stack内存状态为：

aaarticlea/png;base64,iVBORw0KGgoAAAANSUhEUgAAAewAAACGCAIAAACQUC6/AAAdNElEQVR4nO2d/VMUV7qA+X/4B3pxYXWJX8hHcreo3L3UqLCIWZ0YNV4lXoEhucte2zgqwVGIFomSxcwscg1+FQMI7NSENYSUDOhVF1AoNYOGWGGMImWd+8OZ6T79Of01fbqH96n3B2j6a+jup8+8ffq8OQgAAABwLTm0dwAAAAAwDkgcAADAxYDEAQAAXAxdiQfLc3LKg1R3wRQTvtycXN8E7d0AAGDlAhI3A0gcAADKuFXiFurTxKpA4gAAUAYkDhIHAMDF6JH4hC83hyclL3IqJ+QJX25OeZD/E2HqYDk/d1qJi9eT65uQ2w88W3LN6ncF4e7KfiR+D4WGJqYnt0FKPFiedtsAAABWY6glHixP6W3Cl8ubi1AaliPpNzwTOX9SoGklLnQmsSLesMLNpVmfeDbJqrhf+M8p+qTBcv7j5/omhHMCAADYhwGJE8ISOzFYniOym3C6zPzpJS67gFTimhw64cuV2FZlYe7zKMyEp/pc/ngWAAAXo1vigjanMBtBJCCkEs8pD6ayI8KV2Spxcp9lvkBw25BNsUj3VDZfBAAAYB86JS5KGyjKU0XiZlrifE7DuMQliwgWFmRNNLbEJyCbAgAALXRJXOoqofOE02UkbjAnTubWyaS74DmqKYnLNssFuRf1nLjiPwIAACCj6JG4MM8gcrFwqpLEkbB3iji9IoFPOkuyFqn1pHqnaJI4+RH4BchVEZ8n1xcknnKm650CzXEAACjg8LFToCM2AACAGiBxAAAAFyOVuChpIs4gZACVLRqTuP0fAQAAgA4Ob4kDAAAAaoDEAQAAXAxIHAAAwMWAxAEAAFwMSBwAAMDFgMQBAABcDC/xwNdDjIeFMByftF2leCABAFiZ8BKnLsEsCIoHEgCAlYlY4mWN/RAGAiQOAAAVQOIgcQAAXAxIHCQOAICLAYmDxAEAcDEgcZA4AAAuBiQOEgcAwMWAxEHiAAC4GH0S9w4m0GSMqi5jEYQQSnQG6IsbJA4AAHXcJHHvYAKhOBuYngWJAwAAIIT0SHykc55fbHZwRDIxzvJzJjoDuMmMrG81g8QBAABSmGmJj3TOI+5XdhKh+Wkvb/ak072DidR0YYTi4n2RnQ0kDgAAoIwJiQemZ/nWN+nWkc55FAllzLkgcQAAgBQmJB6KI1LijbGIrMT56SBxAAAAi6HXEod0Cm1g8GF3BZWxjnNytJYckJ1TaXHRdO1bMYnG/bF5H0xuXb/EedXGIvwTTsWcODHdogCJWwR1K0HoDSrniS6PS+2sRe50HUp9B1RuLZrgFsBnSTpbJfucpNzNdUEhTT3SOY8ig9OzyT+QKRdzIW68O0jlFK8xw2g74hCOCLonGCkKFd9pVLPlTVFdOFPisk5Oux48cybe2BTlxFdEgMQhMhq2nWC6Gn9am4rKiyitx6JPM+HLzcn1TRjbVYRQsBxPwOswhcpW9H5e8eLcTyBxV1xjFgISd1E45wQzaVipvKQrzITEpeuX1ahg0xO+3JzyoEW7IrstvXcv2XlA4tl2jWkHJO6icMgJJmsZdQ3lKOdYHChxAcFyK5rgYuRvGCq7kW4GGAArq64xXcARd1E44QRTUox6k1Zd4kp3BZO7mkJG4qIdU7kDyd8BTCO7Xe0tcZmJ3E9wSbv9GtMLHHEXBfUTTMUvshpSkbjKzOJfJ3y5xMy5volguTBBHSzPSWY8UunrHHIGsYe5jZI/yH5GYnV4Czi3kpycSrKQ+0cmXpSmi/dB+p+U/nvTzgDV7q0M9QPgNEDiLgq6J5i6XGQ9mF7Q2n5OwslbYHHO0RO+XG4iOYdA4rL6Vtmu8A6AvUzeESZ8uUKdJ/+oNB2RW0eS+xn5JyVA4itU4oPjT0bvPZNO1yJxdhIhRD7hGOmcFwx/xr0owE1JzSz/V+EUCBdIXJdZzEhcaRFFLyvkO4hUtqB3Crly6eakH1MqccHGxBNSm1WYbqYBrj4npFNcf42lJXo7XumP1DRHw2OPyOkajvhI5zyanU8Ih6gEia+UE0xL2xBJWpTcRNEP0l+V/iSaLkqhkM3vHEH7m0e2Ja60FRMSF8Htltx0hU8tO0UJkHi2XWO6iN6O17aPVrBDweGZxMtlpF3igzEFcYPEs/YE06hvbmbpzwYkLj9dnAXndEp0ABQkMORb4ip7qLQnOlvi6aYLtyWTSZHcCJWWFU/kfgKJu+gaM8ydueeHQ7Hyphtt1+7mVR7XJvGRslAcEQPjgMSz+wRTapmqzy/6WUXiaW1FTJcqPDk1t7w8VzbxPOHLtaclLrp1pJ8u/XSKU7Qvi0DibrzGDLO0/GZ8ZiE4POPvnnz74/6i+nDhnk7Vz8Vrl53EY8eDxLP5BBO5NW3DkJsNKatQe0tcZg3CJImgsZ0jECWfw8j1BfmnnDokLt2fdBJHktQJt0NK02W2IjtFCZC4668xYywsLoXHHn3Seevtj/tr20fbw/fbrt19++P+dfv/N6/yuOrnIrSbHHcMJJ7lJ5i8JlS/8qs0upUm6tq6tag3wLXctExu2pjElZZFIHHXXWPaWVp+c+Xm3N62m+VNNw6HYoPjT3Aq/M7c8wp2qD18X3NOnByoMh4RTRHUXI1FEEh8pZxgWrBBynrR9b0hQ1s3tlHF7BP3E0g8m66x8NijCnaotn1U1LmwY2Cqgh0an1lAOh5sctoVjWGZHFeS64AoHKkYJJ7NJxjgHFwgce9gIrWP5NizeNRyp4xG65xrLDz2qNIfqW0fxabmWFhc2tt2s+78GG6PIyMSTx4LgYjJ8YEFA8cLKmujVCpGOIX+gXNLOOcEA5yG0yWuVGfZO5hA8wnnVIdwwjWGNe0NjEhf7YnejlewQ93Rh+REZx5xCNlwwgkGOBNdEh/pnE90BrhCEHGWb20RMg1w5SCSX7S9g8TbIqG4nkI/SvU5YxGU6Aw5qMQP9WtMVtMc4bFHU09+EU0EibsoqJ9ggGPRK3GU0nFS31jTRA22WIT0NTnzZEz44IubRwip+MD0LErMct/BU8/QvIOJ2cERR9Vpo3iNLS2/aem5U9MclWpaHZC4iwIkDiihW+KCp1hczwTe10SQkuV0LOjMkC74d0z6+RsAV6AZJI7Qjz//WtMc9XdPcplu7YDEXRQgcUCJDEhc0LjmJctOIt3PsoT3BtyhjZ0U9Vymf4HRusZ+/PnXSn/kys05Y4uDxF0UIHFACaslLml9J38OxRGKR8TdijWlU1Kaxj0lpiPiBRzRa83+ayzxcrnSHxGNaaULk0M2QtgfFp4/QNZgtcSJtrN3MEEOuBEJ9cvkxNOE9I1B4q8ruCWeeLnsDYwEh2fMrIS6kiD0hkWnj1kePP7pwvXvDrf37mi6AKE96k72fH4xcu+BpOVqDuvTKXgEaoQQmozjviWCboKy2XOVkPR1AYkvLb/xBkY6BqZMrkfDEYdwSjhE4t/emn53/xnqNzO3xybvyYv9P1h1UJzeT9wtYec11tJzx989mX6+dMARd1FQl/jii1cHjnfj3cjbcnT1jjPr94U21l4qrrtK/Z/j/Cht6N1Ye2nD/q413vZVlSfwv/Hd/WceP31u/tCAxK0J266x8ZmFCnbIQF8UKXDEXRR0Jf7seWLzoS8YD5u39djaPX+j/t9we2zY34VVvnb7CfPZFZC4NWHPNba0/KbSH5GttWYAOOIuCooSX3zxCht8VVUzrXZ3Sf11h6zEqiht6C2oOYU9/uDxT2YOEEjcmrDnGrMqkYKBI+6ioCjx3UdC2OClDb1UPvtbu79iNn+66WCPmZUU111dVXlizc6zZb4w9aOZDF+4YPtpxsO+s6d16bXx79ZQKNnKsOKSUWTuacJwIkV2KZC4i4KWxIdG7zEeNm/rMVpt8DXediaViDe8D6UNvfnVLXg9BdtP07obye7YqqpmxsNeuP6d4WMEEneNxNuu3W0P3zew4Oi9ZxXsUMfA1NLyG3I6SNxFQUviuC8KnTy4L7x6xxnGwzKbP83fFmA87KrKE0ZSIqkGb351S96Wo/gH53h8w/4uxsMWeU8uvnhl7BhBOsWayPQ1trT8przpxo8//2ps8R9//vVwKFbBDpGvd2o54rjDKNG5Eyr7ZOcJJkvs/iOsTo07WezrK/H1WfJ5uZRx3pajG2svlfnC2OMG/IvvBKsqTxTXXcVJFe5X6ocVB77HXB6OGTtMIHFrItPXGK6vZnIlU09+qW0frfRHorfjSPt44vPEIJQg8Sw9wWT5/GKE8bBrdp7VuJOljX3FDX3FDeGyRlMqL667irMfqypPcKlwLvNQsP209rx24ftf4jtB8aEr3HrwyvO2HDWZZ7cq1u29wHjYA8e7jR0mkLg1kelrzBsYweY1z+i9Z97AyN62m/k1AU0SH4wpiBsknj0nmCy4Y/iG/V26drW0sb+o3niTvPjQFdxYzq9uETWWi+uu5m09pv2+8tbur3A2puijS4I/pRIseVuObjzQTf3gFh+6wnjYd/efMXaYQOLWRKavsbc/7tcyG65nPz6zEL0d7xiY4sLfPVnbPkpGUX24qD781och1c+V0i4/nCRIPDtPMFlwz0JjzdXihr5N9X0lDfpUXvTRJZy2Lqg5JZs22XSwB89QuOuc+qrWfRjE/zSlm9CanWex4td9GHTC8S2o8hs7TCBxy45B5q6xuacJb2CEnJJ4uTw+sxAee9QxMFV3fgwnSYrqwzXNUexof/ckKfHw2CMsdxxt1+4W1YcL936dt/WY6ufitZuqiQwSz8ITTIl39rQyHtbMM8BiX9+m+r5SbTNv+O9/5Ff5GQ+78b02lYTJxgPdzOZP1R+3bmyK4lW9u/dCciIewENYkaZw1zn8j31r91d0jy/+8mHsMIHErYmMXmOj95590nlr7mkiODzzSeetCnYIV9Fsu3a3Y2AKe1nU80SJhcWluvNjNc3R0XvPtObEBQOQgcSz8ARTAkvc5J6XNvYVN4SL02VXuIbz4UBX2spf6/eF8Mzr98l8ldx0sAdnXT7vuCwcElUs8bJUPprxsIXvf0nx+FKXuGBgrJUZGb3GzvX/y3NkuIIdart2N3o7vrC4ZGw9weGZ8qYbXF9DfRJP1m+KR0RTBGMLk6NUgsRdc4IpYYnEcZQ09G2q7ytWyK4UfnAef8DmnhGN5Ru5fLcoqc3lzWvbrkrGtZaReBnu5Lf5U8bDrt5xhtarQCtU4oJhFGlH5q6xqSe/lP/lxuHQuJmV3Jl7jjMtc08T3ES9EseORuQA7qE4QsKBLfmLBCTujhNMBQsljqO4oU/6zDOZm/aw6xoHlDwrG1zPE0EPlsoTjIcteP+ceFXKEi/TkIvPdIDE6Ye119iPP/86OP6kPXy/pjla0xz9oPWf4zMLhte2sLhU3nRDWj5Cv8TxGPFCEZNlPQRXCFdEG5NMxQin0D9wbonskHiZpBsi93Rx44Fudc/Kxur32vhO374w7juYvy1Q1nJfl8TLiCRMfnWL/cfXTonH+MI6vEBJiSvNkOgMcH+Ks/wVTl7JGpftFwkCOwX7hZjH1jB2jc09TeCMNn78+Ennrb1tN/HzSX/3ZHf0IW441zRHDb/mowI8BXFRZI3EcXDdEDfWXsKpjLd2f0V6li9LoHSzD0zPIrT0enlH0wXGw/6b9zPcazA5xotU2UoST1Us+PbWNP4n76TRWcU2iZPtMnH2MxJKM4PIv/hP7CT3b9W8LFHznnc9Vz2ZUjAe9rfbTpIdQlR6+JU33cA9/HCK45POWx0DU8HhmfGZBTLdwVHedMPY0VUHJO6iyDKJ48DdENfv+7swnZKYFe+I2ONEi40fZJHxsPncGC/aJM6tJ3b/UUGVn/Gwn1+MIH3Vx6wJuyQuFCXh0JTE084gni4qzqlt2dRhkEic5sNVxsOu+tNnShIX9fDTNYgVrmdv7OiqAxJ3UWSlxHEU+/oK93QyHpbZcvSbW9MIISSsrIuQ8Pl5su3M66K4bnDdrta1208Ez/QI5lGXeKoNfrH9Ck6Ir9l5NvUNwO4WoV0SlxY1Fnk27QyN/WVqxTnTL1sWistLnDgkVB6dZe4aw/0LM7FmkLiLIoslXtbYX9rY9/td5xgPm1/lv/fggaDdjc1AyJedRNK2+aYjY9/cmha16tQljn39/eXB5LPQ7afLGvtFqQLbgk5LnAj5lrjMDI39Zdpa4krLqkmcOFT2N8kzd40dDsW6ow8zsWaQuIsiuyWOY/UHXzEe9ndV/m3k2/Zi+YoejwvhZksv8ZHOebT4YqHkvdSz0FTnQpmn95kP23LisYj8ZxMUs1edIfU/kqmwrGlZscRlnjXHIjS6PWToGsMdSwx3DFeHoT1yL4TeyMRpoILNEi8LTNewQQaPe1V3jdROBiQeG3y9vPvIV4y03gVu+9vb841S7xQkeHNPpneK/AxKEte0LClxQbdlIhuTTemU7uhDC0v5iKhu7KBuJQjt8c6e1gydCUrYL/Gp18uba9sYD/vb6s821V0va+xTkHi6hpqGlvgWfw/jYddVi8ekze6WOIRi4P+e+ctGRKU/cmfOgnrYAGAA+yU+i9Diw7u/SyWpi+p6S3zR/pfL0lx2mpRpOonjF4XWbj8x3CV6iTS7c+IQypEJiUdvx0XjXgGAnVCROJqf3kYMOVvcMPIf/siVgR94Hae+dgs9S/ZLTiPx5Cv7W45+f3tWtJ5k7xQ9LxxZEiBx+mG5xHFhezMvagKASWhJ3CsYcvbv/S+XW4I33yZGQ2QVUoxaJP7vqZG21u8LKayHwkM1kDj9sFziLT13WnruWLhCANALRYmXEUPO/vX6d2h+ukY0GqK4U7LQvAoS/3Y4+hvRMLai9djeBscBEqcf1kp8fGah0h/ROLosAGQIuyUuCemQs+qjIaqH9oIS9oeVEocwE5ZcOZBIARwCdYmXNfav3fM3xiMeclZ2NET10FvaDSS+QsP8ZbO0/Kbu/FjbtbvmVwUAJnGCxMvkhpwt01mUmR+iVk+RZbdKnPqHcWlYInFs8Mx1DAcAXThE4hsPdOPrS1rHR2NR5k0He/ixEml/HNkAidMP8xIHgwNOwwkS1+JfLUWZuTuBE8oiSwMkTj9MShwMDjgQ6hIvrruafBSpoQBm2qLMyTKekopuTgiQOP0wI/G5p4ma5ih0KAScBl2Jl9Rfx2pb/V6bxkXSFmVOFvPc/CmZXndCgMTph2GJX7k5V8EOSWunAQB1KEq8tKEX11orqDml91GkejfENd52xsPmceUjnBEgcfphQOKJl8uHQ7G9bTdlq/kAAHWoSdwXxrXW8qtbDJctVumGmCzkVnmCSk1k2chWidOpv2wsdEl8aflNd/RhBTvUHr4Pb/QAjoWWxFfvOMNw5Y9NrEexG6IvnL8tgG8SDulxaJ/E7S0wT0Hihj+gdoljfdedH5t68ouxYwYA9kBF4oW7zkl7hZsJ2W6IpQ29q6qandNzHCRuWWRO4omXy+GxR5X+SG37KLyNCbgC+yXOv59Ze8naNUu7ITrqHU57JC4oqEFWbEjB1XYY6ZxPdAa4Cg9ahgQjykHwDlWoNSGYgdxQnOX3h9yodFnpgkofUGsoSfzHn3/tjj6sbR99++P+w6EY6BtwETZLnBspZcP+rgxtQtQN0TmjqdBqiY90zvNKZSe5AcCwDZNOVyiiRsZI5zwnTXJQYE7iajOIFIz/JNoZybKSBVOfwkxLPG/rsfGZhSs35zoGptrD92vbR2uaoxXsUEvPnehtSRloAHA8dkqcG7OQH19QV/jCGp9Sljb2Ff8l0hCKLTy471XfrnQoxIwFJYmLShsHpmeT7V9hGoSfrhDC9RCbkK+/LDODdN8U6i+n5pEsqF58WUMwHja/5nRt+6i/e7JjYKpjYGp8ZgGy3oCrsU3i5lvEBdtP63hKGZjuGn9SeWSwoqGvTOUbQPZLXFAes5+oUCzKZaerXCweFxiJHZ12BpV9k19Wtfhyhh9sAoBbsEfi5nPTa3aexReg1qeUgelZhJaeTFWkuiEma/2IcvHZL/HMtMSJkG+Jy8wg3TeFlrjsgiBxAJDFBombH1+QewlTx52AsDPXDVFmrMSslbiw2Dz3AFApJ05MVwrBeojgVJt2htS+yXxLkF1WVeKGjhlIHMg+bJA4fu+G8bDGuoSvS9Va27C/S0dORmLn0sb+orpefBtYVdWcvJ1kpcS5nh7ko8Ik/Ecd6ZxHkcHp2eQfZBvR8qtFgpUr9E6Rn0El1SNdVlHikg+oNUDiQPZhg8SLz029u1/8ao93MIEk16B04samKL7uLvb/gBBCKP6ftZcETykD07N4kYBQR1KJN/QW1JxiPOyqrUdbv/kBkUtlncS1hJvetLQqQOJA9mFLTjzW9+JVdWM7mcqQLTnPTiKy6/DW4L8KqvyMh/38ItlIQ63NXQw3+DiW+GR8lv+7jMSL667icVre2dN6Z2a+peeONzDC9wYGia+QAIkD2Yc9DzbZSbT0ennLh6eTjxYPDMi9YhKLIEK7x2KF208wHvb9g2fJ9SCEEIrXcG8MNUXl8wGExDcd7MEC3Xzoi2fPE1hcpY19fzj2z8Oh2MLiEkhceAwk6M1aODZA4kD2YY/EcZ4ETca4TiaXh2ORyTgi/RDify2pv/57byvjYd/76HOpeRBCkVDq3f2tx4YfxGUyuimJb6m9hNPoJf91YfHFK5GOSo7e8vgjHZe/35l5gThN4isxQOJA9mFTP3GiXZzsauJh9/71GpnxwK3sSAgPURtgPGx147mOFnFvFjJvjm8JJXtaH9+NiZvSgelZhIYG/vGbzZ8yHnb1ji86Hi/LvFsemJ5aftNx+fsynUWZDQRInH6AxIHsw66XfXALOtlBue5KDF9N2wK9ZB8zhOL/kxqitmhP6+KLOZkeE/i9ENzBwRcueP8c42Hf/fDUn0Uvcwamz/b/gLdS+P6Xwh0QzIZvJNv1FGU2FlDt3ilh9qIBACdh2xubfAs6MD2LUNeXl3EnkwPHuwe/Didlmsq35G093nr3ueygTOIeLC33/3joC8bDvrUtQHZCL6y9hC/YPyTrdqaROG7IayzKTFPi1Y0d1CXo6nhnT6v5ywYAnIN9Y6dwugzFEUKRUH/RR5dwr+3q2rY/9y4ghA428kPU4uyK7PsfCAneNPy/F6/e2XWSwS8TNfaXpdIs+VX+y1cGuDSL/ArluhhqKcpMTeIAAAAkNg6AlXxDMDKJuOeQxYdurNvVynjYP9Z+Efj6GuMhahynhtMgO1DIdEwMTM8i9Phu7LdbjjIeds3Os8l3i7Yc/ebWtGDO5Ar5xnjycSuS72KYtigzSBwAAPrYOYohL01i3Atf9PnmQ19wX3bX7wuJlS1GmBJJNaX/dLAH52eSbfkjY5ImtmAk6iTzCZWXfdIWZQaJAwBAGVvHE0+9VCnIaYTiiy9e7Wi6wMgOFSsa3k5qWyIfgoecTb4XqvAqJnlj4Ab8UO8nrl6UGSQOAABNkhKnXr3MFybb4IZjw/6uDFVGVinKrDHwAwBjhwkkDgCAPDiVYbJa8QoJxaLM2oIx0b0NJA4AgDy7j4QYD5t8lgihSeVGuiGW1F83070NJA4AgDzHOwYYD1v4wXnqcnRX6O2GiEsL7Wi6YOwwgcQBAJDn21vTjIfNr26hrkU3RrFPa5Mcd10XDceoHZA4AADyLL1exsO98sVuIKyOkvrreAiXB49/MnaYQOIAACjyZc9IsjFOvY9Klsbq99oYD3u4vdfwMQKJAwCgyNLr5U3ek4yHXb3jDHXfZV+s3fM3xsMWVPmfPU+kPxgKgMQBAFDj3oM4Tqqs2XkW2uOWG5zxsJeHY2YOEEgcAIA0DI3ewx4vqDkF+XHzUVJ/ffWOM9jghp9ncoDEAQBIT+z+o7XbT2DvrNl5dv2+UIbefszu2LC/a423HT/JLKjyp0o8mwIkDgCAJhZfvAp8PYSb5FysqmouqDkFkTZwHTgu6k72PH763JLjAhIHAEAHj58+/7JnBA9KBaE3qhs7Al8PGe5NKAtIHAAAwMX8P2FDhF0ERaFTAAAAAElFTkSuQmCC" alt="" />

可以看出上图中的argument_stack与刚被初始化之后是一样的。此时argument_stack真正做好了迎接下一次函数调用的准备。

回到文章刚开始的问题...

为何无需free(str)呢？弄明白了argument_stack之后就很好理解这个问题了。

因为str指向的是zval中实际存放“hello world”的内存地址。假设扩展函数如下：

PHP_FUNCTION(test)
{
    char*  str;
    int    str_len;

    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s", &str, &str_len) == FAILURE) {
        RETURN_FALSE;
    }

    str[] = 'H';
}

则调用

$a = "hello world";
test($a);
echo $a;

会输出“Hello world”。尽管我们调用test的时候，并非是传 $a 的引用，但实际效果相当于 test(&$a) 。

简单来说，内存中只有一份 $a ，不管是CV数组中，还是在argument_stack中。而zend_parse_parameters并没有拷贝一份数据用于函数执行，事实上它也不能这么做。因此，当函数完毕之后，如果没有其他地方会用到$a，php清理argument_stack时会帮我们free。如果仍然其他代码在使用，就更加不能手动free了，否则会破坏 $a 的内存区域。

需要注意的是，并非写扩展函数中用到的每个变量，php都会自动回收。所以该free的时候，切勿手软:)