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In-depth analysis of PHP execution principle (4): function calling, in-depth analysis of PHP

WBOY
Release： 2016-07-06 14:25:31
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深入剖析php执行原理（4）：函数的调用，深入剖析php

本章开始研究php中函数的调用和执行，先来看函数调用语句是如何被编译的。

我们前面的章节弄明白了函数体会被编译生成哪些zend_op指令，本章会研究函数调用语句会生成哪些zend_op指，等后面的章节再根据这些op指令，来剖析php运行时的细节。

源码依然取自php5.3.29。

函数调用

回顾之前用的php代码示例：

<?<span>php
</span><span>function</span> foo(<span>$arg1</span><span>)
{
    </span><span>print</span>(<span>$arg1</span><span>);
}

</span><span>$bar</span> = 'hello php'<span>;
foo(</span><span>$bar</span>);
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在函数编译一章里已经分析过，函数foo最终会编译生成对应的zend_function，存放于函数表(CG(function_table))中。

现在开始看 foo($bar); 一句，这应该是最简单的函数调用语句了。其他还有一些形式更为复杂的函数调用，例如以可变变量作为函数名，例如导入的函数以别名进行调用（涉及到命名空间），再例如以引用作为参数，以表达式作为参数，以函数调用本身作为参数等等。

我们从简单的来入手，弄清楚调用语句的编译过程及产出，对于复杂的一些调用，下文也争取都能谈到一些。

1、语法推导

就 foo($bar); 而言，其主要部分语法树为：

绿色的节点表示最后对应到php代码中的字面。红色的部分是语法推导过程中最重要的几步，特别是function_call。

我们从语法分析文件zend_language_parser.y中挑出相关的：

function_call:
		namespace_name '(' { $2.u.opline_num = zend_do_begin_function_call(&$1, 1 TSRMLS_CC); }
				function_call_parameter_list
				')' { zend_do_end_function_call(&$1, &$$, &$4, 0, $2.u.opline_num TSRMLS_CC); zend_do_extended_fcall_end(TSRMLS_C); }
	|	T_NAMESPACE T_NS_SEPARATOR namespace_name '(' { $1.op_type = IS_CONST; ZVAL_EMPTY_STRING(&$1.u.constant);  zend_do_build_namespace_name(&$1, &$1, &$3 TSRMLS_CC); $4.u.opline_num = zend_do_begin_function_call(&$1, 0 TSRMLS_CC); }
				function_call_parameter_list
				')' { zend_do_end_function_call(&$1, &$$, &$6, 0, $4.u.opline_num TSRMLS_CC); zend_do_extended_fcall_end(TSRMLS_C); }
	|	T_NS_SEPARATOR namespace_name '(' { $3.u.opline_num = zend_do_begin_function_call(&$2, 0 TSRMLS_CC); }
				function_call_parameter_list
				')' { zend_do_end_function_call(&$2, &$$, &$5, 0, $3.u.opline_num TSRMLS_CC); zend_do_extended_fcall_end(TSRMLS_C); }
	|	class_name T_PAAMAYIM_NEKUDOTAYIM T_STRING '(' { $4.u.opline_num = zend_do_begin_class_member_function_call(&$1, &$3 TSRMLS_CC); }
			function_call_parameter_list
			')' { zend_do_end_function_call($4.u.opline_num?NULL:&$3, &$$, &$6, $4.u.opline_num, $4.u.opline_num TSRMLS_CC); zend_do_extended_fcall_end(TSRMLS_C);}
	|	class_name T_PAAMAYIM_NEKUDOTAYIM variable_without_objects '(' { zend_do_end_variable_parse(&$3, BP_VAR_R, 0 TSRMLS_CC); zend_do_begin_class_member_function_call(&$1, &$3 TSRMLS_CC); }
			function_call_parameter_list
			')' { zend_do_end_function_call(NULL, &$$, &$6, 1, 1 TSRMLS_CC); zend_do_extended_fcall_end(TSRMLS_C);}
	|	variable_class_name T_PAAMAYIM_NEKUDOTAYIM T_STRING '(' { zend_do_begin_class_member_function_call(&$1, &$3 TSRMLS_CC); }
			function_call_parameter_list
			')' { zend_do_end_function_call(NULL, &$$, &$6, 1, 1 TSRMLS_CC); zend_do_extended_fcall_end(TSRMLS_C);}
	|	variable_class_name T_PAAMAYIM_NEKUDOTAYIM variable_without_objects '(' { zend_do_end_variable_parse(&$3, BP_VAR_R, 0 TSRMLS_CC); zend_do_begin_class_member_function_call(&$1, &$3 TSRMLS_CC); }
			function_call_parameter_list
			')' { zend_do_end_function_call(NULL, &$$, &$6, 1, 1 TSRMLS_CC); zend_do_extended_fcall_end(TSRMLS_C);}
	|	variable_without_objects  '(' { zend_do_end_variable_parse(&$1, BP_VAR_R, 0 TSRMLS_CC); zend_do_begin_dynamic_function_call(&$1, 0 TSRMLS_CC); }
			function_call_parameter_list ')'
			{ zend_do_end_function_call(&$1, &$$, &$4, 0, 1 TSRMLS_CC); zend_do_extended_fcall_end(TSRMLS_C);}
;<br /><br />function_call_parameter_list:<br />        non_empty_function_call_parameter_list    { $$ = $1; }<br />    |    /* empty */                　　　　　　　　{ Z_LVAL($$.u.constant) = 0; }<br />;<br /><br /><br />non_empty_function_call_parameter_list:<br />        expr_without_variable    { Z_LVAL($$.u.constant) = 1;  zend_do_pass_param(&$1, ZEND_SEND_VAL, Z_LVAL($$.u.constant) TSRMLS_CC); }<br />    |    variable                { Z_LVAL($$.u.constant) = 1;  zend_do_pass_param(&$1, ZEND_SEND_VAR, Z_LVAL($$.u.constant) TSRMLS_CC); }<br />    |    '&' w_variable          { Z_LVAL($$.u.constant) = 1;  zend_do_pass_param(&$2, ZEND_SEND_REF, Z_LVAL($$.u.constant) TSRMLS_CC); }<br />    |    non_empty_function_call_parameter_list ',' expr_without_variable    { Z_LVAL($$.u.constant)=Z_LVAL($1.u.constant)+1;  zend_do_pass_param(&$3, ZEND_SEND_VAL, Z_LVAL($$.u.constant) TSRMLS_CC); }<br />    |    non_empty_function_call_parameter_list ',' variable                 { Z_LVAL($$.u.constant)=Z_LVAL($1.u.constant)+1;  zend_do_pass_param(&$3, ZEND_SEND_VAR, Z_LVAL($$.u.constant) TSRMLS_CC); }<br />    |    non_empty_function_call_parameter_list ',' '&' w_variable           { Z_LVAL($$.u.constant)=Z_LVAL($1.u.constant)+1;  zend_do_pass_param(&$4, ZEND_SEND_REF, Z_LVAL($$.u.constant) TSRMLS_CC); }<br />;
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其结构并不复杂：

1）function_call这条推导，代表了一个完整的函数调用。

2）namespace_name是指经过命名空间修饰过之后的函数名，由于我们的例子中，函数foo并没有处于任何一个命名空间里，所以namespace_name其实就是foo。如果我们的函数定义在命名空间中，则namespace_name是一个类似“全路径”的fullname。

<span>namespace MyProject
{
</span><span>function</span> foo(<span>$arg1</span><span>)
{
    </span><span>print</span>(<span>$arg1</span><span>);
}
}

namespace
{
</span><span>$bar</span> = 'hello php'<span>;</span>
MyProject\foo(<span>$bar</span><span>);<span>//<span> 以类似&ldquo;全路径&rdquo;的fullname来调用函数，则namespace_name为MyProject\foo</span></span> 
}</span>
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3）function_call_parameter_list是函数的参数列表，而non_empty_function_call_parameter_list则代表了非空参数列表。

4）从这些推导产生式里，我们还能看出编译时的所运用的一些关键处理：

zend_do_begin_function_call-->zend_do_pass_param-->zend_do_end_function_call<br /><br />        开始                        解析参数                     结束
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和编译function语句块时的几步（zend_do_begin_function_declaration->zend_do_receive_arg->zend_do_end_function_declaration等）顺序上比较类似。

上面提到语法树我们仅仅画了一部分，准确讲，没有将namespace以及function_call_parameter_list以下的推导过程进一步画出来。原因一是namespace的推导比较简单。第二，由于function_call_parameter_list-->variable这步会回到variable上，而variable经过若干步一直到产生变量$bar的推导比较复杂，也不是本文的重点，所以这里就不一进步探究了。

2、开始编译

看下function_call的推导式，一开始，zend vm会执行zend_do_begin_function_call做一些函数调用的准备。

2.1、 zend_do_begin_function_call

代码注解如下：

zend_function *<span>function;
</span><span>char</span> *<span>lcname;
</span><span>char</span> *is_compound = memchr(Z_STRVAL(function_name->u.constant), <span>'</span><span>\\</span><span>'</span>, Z_STRLEN(function_name-><span>u.constant));

</span><span>//</span><span> 将函数名进行修正，例如带上命名空间作为前缀等</span>
<span>zend_resolve_non_class_name(function_name, check_namespace TSRMLS_CC);

</span><span>//</span><span> 能进入该分支，说明在一个命名空间下以shortname调用函数，会生成一条DO_FCALL_BY_NAME指令</span>
<span>if</span> (check_namespace && CG(current_namespace) && !<span>is_compound) {
        </span><span>/*</span><span> We assume we call function from the current namespace
        if it is not prefixed. </span><span>*/</span>

        <span>/*</span><span> In run-time PHP will check for function with full name and
        internal function with short name </span><span>*/</span><span>
        zend_do_begin_dynamic_function_call(function_name, </span><span>1</span><span> TSRMLS_CC);
        </span><span>return</span> <span>1</span><span>;
} 

</span><span>//</span><span> 转成小写，因为CG(function_table)中的函数名都是小写</span>
lcname = zend_str_tolower_dup(function_name->u.constant.value.str.val, function_name-><span>u.constant.value.str.len);

</span><span>//</span><span> 如果function_table中找不到该函数，则也尝试生成DO_FCALL_BY_NAME指令</span>
<span>if</span> ((zend_hash_find(CG(function_table), lcname, function_name->u.constant.value.str.len+<span>1</span>, (<span>void</span> **) &function) == FAILURE) ||<span>
    ((CG(compiler_options) </span>& ZEND_COMPILE_IGNORE_INTERNAL_FUNCTIONS) && (function->type ==<span> ZEND_INTERNAL_FUNCTION))) {
        zend_do_begin_dynamic_function_call(function_name, </span><span>0</span><span> TSRMLS_CC);
        efree(lcname);
        </span><span>return</span> <span>1</span>; <span>/*</span><span> Dynamic </span><span>*/</span><span>
} 
efree(function_name</span>-><span>u.constant.value.str.val);
function_name</span>->u.constant.value.str.val =<span> lcname;

</span><span>//</span><span> 压入CG(function_call_stack)</span>
zend_stack_push(&CG(function_call_stack), (<span>void</span> *) &function, <span>sizeof</span>(zend_function *<span>));
zend_do_extended_fcall_begin(TSRMLS_C);
</span><span>return</span> <span>0</span>;
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有几点需要理解的：

1，zend_resolve_non_class_name。由于php支持命名空间、也支持别名/导入等特性，因此首先要做的是将函数名称进行修正，否则在CG(function_table)中找不到。例如，函数处于一个命名空间中，则可能需要将函数名添加上命名空间作为前缀，最终形成完整的函数名，也就是我们前文提到的以一种类似“全路径”的fullname作为函数名。再例如，函数名只是一个设置的别名，它实际指向了另一个命名空间中的某个函数，则需要将其改写成真正被调用函数的名称。这些工作，均由zend_resolve_non_class_name完成。命名空间添加了不少复杂度，下面是一些简单的例子：

<?<span>php
namespace MyProject;

</span><span>function</span> foo(<span>$arg1</span><span>)
{
    </span><span>print</span>(<span>$arg1</span><span>);
}

</span><span>$bar</span> = 'hello php'<span>;<br />
foo(</span><span>$bar</span>);                 <span>//</span><span> zend_resolve_non_class_name会将foo处理成MyProject\foo</span><span>
namespace\foo(</span><span>$bar</span>);       <span>//</span><span> 在进入zend_do_begin_function_call之前，<span>函数名已经</span>被扩展成<span><span>\<span>MyProject\foo</span></span></span>，再经过zend_resolve_non_class_name，<span>将\<span>MyProject\foo</span></span>处理成MyProject\foo</span><span>
\MyProject\foo(</span><span>$bar</span>);      <span>//</span><span> zend_resolve_non_class_name会将<span><span>\<span>MyProject\foo</span></span></span>处理成MyProject\foo</span>
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总之，zend_resolve_non_class_name是力图生成一个最精确、最完整的函数名。

2，CG(current_namespace)存储了当前的命名空间。check_namespace和!is_compound一起说明被调用函数在当前命名空间下的，并且以shortname名称被调用。所谓shortname，是和上述的fullname相对，shorname的函数名，不存在"\"。

就像上面的例子中，我们在MyProject命名空间下，以foo为函数名来调用。这种情况下，check_namespace=1，is_compound = NULL，CG(current_namespace) = MyProject。因此，会走到zend_do_begin_dynamic_function_call里进一步处理。zend_do_begin_dynamic_function_call我们下面再具体描述。

<?<span>php
namespace MyProject\sub;

</span><span>function</span> foo(<span>$arg1</span><span>)
{
    </span><span>print</span>(<span>$arg1</span><span>);
}

namespace MyProject;
</span><span>$bar</span> = 'hello php'<span>;
sub\foo(</span><span>$bar</span>);      <span>//</span><span> 以sub\foo调用函数，并不算shortname，因为存在\</span>
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注意上述例子，我们以sub\foo来调用函数。zend_resolve_non_class_name会将函数名处理成MyProject\sub\foo。不过is_compound是在zend_resolve_non_class_name之前算的，由于sub\foo存在"\"，所以is_compound为"\foo"，!is_compound是false，因而不能进入zend_do_begin_dynamic_function_call。

3，同样，如果CG(function_table)中找不到函数，也会进入zend_do_begin_dynamic_function_call进一步处理。为什么在函数表中找不到函数，因为php允许我们先调用，再去定义函数。例如：

<?<span>php
</span><span>$bar</span> = 'hello php'<span>;

</span><span>//</span><span> 先调用</span>
foo(<span>$bar</span><span>);

</span><span>//</span><span> 后定义</span>
<span>function</span> foo(<span>$arg1</span><span>)
{
    </span><span>print</span>(<span>$arg1</span><span>);
}</span>
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4，在zend_do_begin_function_call的最后，我们将函数压入CG(function_call_stack)。这是一个栈，因为在后续对传参的编译，我们仍然需要用到函数，所以这里将其压亚入栈中，方便后面获取使用。之所以用栈，是因为调用函数传递的参数，可能是另一次函数调用。为了确保参数总是能找到对应的函数，所以用栈。

<?<span>php
</span><span>function</span> foo(<span>$arg1</span><span>)
{
    </span><span>print</span>(<span>$arg1</span><span>);
}

</span><span>$bar</span> = 'hello php'<span>;
foo(</span><span>strlen</span>(<span>$bar</span>));   <span>//</span><span> 首先foo入栈，然后分析参数strlen($bar)，发现依然是个函数，于是strlen入栈，再分析参数$bar，此时弹出对应的函数正好为strlen。</span>
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2.2、 zend_do_begin_dynamic_function_call

前面提到，正常的调用，会先执行zend_do_begin_function_call，在zend_do_begin_function_call中有两种情况会进一步调用zend_do_begin_dynamic_function_call来处理。

一是，在命名空间中，以shortname调用函数；

二是，在调用函数时，尚未定义函数。

其实还有第三种情况会走到zend_do_begin_dynamic_function_call，就是当我们调用函数的时候，函数名并非直接写成字面，而是通过变量等形式来间接确定。这种情况下，zend vm会直接执行zend_do_begin_dynamic_function_call。

举例1：

<?<span>php
</span><span>function</span> foo(<span>$arg1</span><span>)
{
    </span><span>print</span>(<span>$arg1</span><span>);
}

</span><span>$bar</span> = 'hello php'<span>;
</span><span>$func</span> = 'foo'<span>;
</span><span>$func</span>(<span>$bar</span>);          <span>//</span><span> 我们以变量$func作为函数名，试图调用函数foo，$func类型是IS_CV</span>
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此时， $func($bar) 对应function_call语法推导式的最后一条：

function_call:<br />        ...
	|	variable_without_objects  '(' { zend_do_end_variable_parse(&$1, BP_VAR_R, 0 TSRMLS_CC); zend_do_begin_dynamic_function_call(&$1, 0 TSRMLS_CC); }
			function_call_parameter_list ')'
			{ zend_do_end_function_call(&$1, &$$, &$4, 0, 1 TSRMLS_CC); zend_do_extended_fcall_end(TSRMLS_C);}
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推导式中的variable_without_objects对应的就是变量 $func 。$func其实是一个compiled_variable，并且在op_array->vars数组中索引为1，索引为0的是在它之前定义的变量 $bar 。

举例2：

<span>function</span> foo(<span>$arg1</span><span>)
{
    </span><span>print</span>(<span>$arg1</span><span>);
}

</span><span>$bar</span> = 'hello php'<span>;
</span><span>$func</span> = 'foo'<span>;
</span><span>$ref_func</span> = 'func'<span>;
$</span><span>$ref_func</span>(<span>$bar</span>); <span>//</span><span> 以可变变量的形式来调用函数，$$ref_func类型是IS_VAR</span>
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该例是以可变变量来调用函数，和例1一样， $$ref_func($bar)也是对应function_call语法推导式的最后一条，所以不会走进zend_do_begin_function_call，而是直接进入zend_do_begin_dynamic_function_call。不同的点在于 $$ref_func 节点类型不再是compiled_variable，而是普通的variable，标识为IS_VAR。

下面的图画出了5种case，第1种不经过zend_do_begin_dynamic_function_call，而后4种会调用zend_do_begin_dynamic_function_call处理，注意最后2种不经过zend_do_begin_function_call：

具体看下zend_do_begin_dynamic_function_call的代码：

<span>void</span> zend_do_begin_dynamic_function_call(znode *function_name, <span>int</span> ns_call TSRMLS_DC) <span>/*</span><span> {{{ </span><span>*/</span><span>
{
    unsigned </span><span>char</span> *ptr =<span> NULL;
    zend_op </span>*opline, *<span>opline2;

    </span><span>//</span><span> 拿一条zend_op</span>
    opline =<span> get_next_op(CG(active_op_array) TSRMLS_CC);
    
    </span><span>//</span><span> 参数ns_call表名是否以shortname在命名空间中调用函数</span>
    <span>if</span><span> (ns_call) {
        </span><span>char</span> *<span>slash;
        </span><span>int</span><span> prefix_len, name_len;
        </span><span>/*</span><span> In run-time PHP will check for function with full name and
           internal function with short name </span><span>*/</span>
        
        <span>//</span><span> 第一条指令是ZEND_INIT_NS_FCALL_BY_NAME</span>
        opline->opcode =<span> ZEND_INIT_NS_FCALL_BY_NAME;
        opline</span>->op2 = *<span>function_name;
        opline</span>->extended_value = <span>0</span><span>;
        opline</span>->op1.op_type =<span> IS_CONST;
        Z_TYPE(opline</span>->op1.u.constant) =<span> IS_STRING;
        Z_STRVAL(opline</span>->op1.u.constant) = zend_str_tolower_dup(Z_STRVAL(opline->op2.u.constant), Z_STRLEN(opline-><span>op2.u.constant));
        Z_STRLEN(opline</span>->op1.u.constant) = Z_STRLEN(opline-><span>op2.u.constant);
        opline</span>->extended_value = zend_hash_func(Z_STRVAL(opline->op1.u.constant), Z_STRLEN(opline->op1.u.constant) + <span>1</span><span>);
        
        </span><span>//</span><span> 再拿一条zend_op，指令为ZEND_OP_DATA</span>
        slash = zend_memrchr(Z_STRVAL(opline->op1.u.constant), <span>'</span><span>\\</span><span>'</span>, Z_STRLEN(opline-><span>op1.u.constant));
        prefix_len </span>= slash-Z_STRVAL(opline->op1.u.constant)+<span>1</span><span>;
        name_len </span>= Z_STRLEN(opline->op1.u.constant)-<span>prefix_len;
        opline2 </span>=<span> get_next_op(CG(active_op_array) TSRMLS_CC);
        opline2</span>->opcode =<span> ZEND_OP_DATA;
        opline2</span>->op1.op_type =<span> IS_CONST;
        Z_TYPE(opline2</span>->op1.u.constant) =<span> IS_LONG;
        </span><span>if</span>(!<span>slash) {
            zend_error(E_CORE_ERROR, </span><span>"</span><span>Namespaced name %s should contain slash</span><span>"</span>, Z_STRVAL(opline-><span>op1.u.constant));
        }
        </span><span>/*</span><span> this is the length of namespace prefix </span><span>*/</span><span>
        Z_LVAL(opline2</span>->op1.u.constant) =<span> prefix_len;
        </span><span>/*</span><span> this is the hash of the non-prefixed part, lowercased </span><span>*/</span><span>
        opline2</span>->extended_value = zend_hash_func(slash+<span>1</span>, name_len+<span>1</span><span>);
        SET_UNUSED(opline2</span>-><span>op2);
    } </span><span>else</span><span> {
        </span><span>//</span><span> 第一条指令是ZEND_INIT_FCALL_BY_NAME</span>
        opline->opcode =<span> ZEND_INIT_FCALL_BY_NAME;
        opline</span>->op2 = *<span>function_name;
        
        </span><span>//</span><span> 先调用，再定义</span>
        <span>if</span> (opline->op2.op_type ==<span> IS_CONST) {
            opline</span>->op1.op_type =<span> IS_CONST;
            Z_TYPE(opline</span>->op1.u.constant) =<span> IS_STRING;
            Z_STRVAL(opline</span>->op1.u.constant) = zend_str_tolower_dup(Z_STRVAL(opline->op2.u.constant), Z_STRLEN(opline-><span>op2.u.constant));
            Z_STRLEN(opline</span>->op1.u.constant) = Z_STRLEN(opline-><span>op2.u.constant);
            opline</span>->extended_value = zend_hash_func(Z_STRVAL(opline->op1.u.constant), Z_STRLEN(opline->op1.u.constant) + <span>1</span><span>);
        }
        </span><span>//</span><span> 以变量当函数名来调用</span>
        <span>else</span><span> {
            opline</span>->extended_value = <span>0</span><span>;
            SET_UNUSED(opline</span>-><span>op1);
        }
    }

    </span><span>//</span><span> 将NULL压入CG(function_call_stack)</span>
    zend_stack_push(&CG(function_call_stack), (<span>void</span> *) &ptr, <span>sizeof</span>(zend_function *<span>));
    zend_do_extended_fcall_begin(TSRMLS_C);
}</span>
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ns_call参数取值为0或者1。如果在命名空间中，以shortname调用函数，则ns_call = 1，并且会生成2条指令。如果是先调用再定义，或者以变量作函数名，则ns_call = 0，并且只会生成1条指令。

以ns_call = 1为例：

<?<span>php
namespace MyProject;

</span><span>function</span> foo(<span>$arg1</span><span>)
{
    </span><span>print</span>(<span>$arg1</span><span>);
}

</span><span>$bar</span> = 'hello php'<span>;
foo(</span><span>$bar</span>);
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生成的op指令如下所示：

php $bar = 'hello php'; foo($bar); function foo($arg1) { print($arg1); }

生成的op指令如下所示：

php function foo($arg1) { print($arg1); } $bar = 'hello php'; $func = 'foo'; $func($bar);

生成的op指令如下所示：

void zend_do_pass_param(znode *param, zend_uchar op, int offset TSRMLS_DC) /* {{{ */ { zend_op *opline; int original_op = op; zend_function **function_ptr_ptr, *function_ptr; int send_by_reference; int send_function = 0; // 从CG(function_call_stack)获取当前函数，注意可能拿出的是NULL zend_stack_top(&CG(function_call_stack), (void **) &function_ptr_ptr); function_ptr = *function_ptr_ptr; // 调用的地方以引用传参，但是php.ini中配置不允许这样，则抛错 if (original_op == ZEND_SEND_REF && !CG(allow_call_time_pass_reference)) { if (function_ptr && function_ptr->common.function_name && function_ptr->common.type == ZEND_USER_FUNCTION && !ARG_SHOULD_BE_SENT_BY_REF(function_ptr, (zend_uint) offset)) { zend_error(E_DEPRECATED, "Call-time pass-by-reference has been deprecated; " "If you would like to pass it by reference, modify the declaration of %s(). " "If you would like to enable call-time pass-by-reference, you can set " "allow_call_time_pass_reference to true in your INI file", function_ptr->common.function_name); } else { zend_error(E_DEPRECATED, "Call-time pass-by-reference has been deprecated"); } }

1，首先是从CG(function_call_stack)中获取当前参数对应的函数。注意，可能拿到的只是一个NULL。因为php的语法允许我们先函数调用，再接着对函数进行定义。如前文所述，这种情况下zend_do_begin_function_call中会向CG(function_call_stack)中压入NULL，同时会产生DO_FCALL_BY_NAME指令。

2，在传参的语法推导式中，op可能会有3种，分别是ZEND_SEND_VAL、ZEND_SEND_VAR、ZEND_SEND_REF。

expr_without_variable    { Z_LVAL($$.u.constant) = <span>1</span>;  zend_do_pass_param(&$<span>1</span><span>, ZEND_SEND_VAL, Z_LVAL($$.u.constant) TSRMLS_CC); }
variable                 { Z_LVAL($$.u.constant) </span>= <span>1</span>;  zend_do_pass_param(&$<span>1</span><span>, ZEND_SEND_VAR, Z_LVAL($$.u.constant) TSRMLS_CC); }
</span><span>'</span><span>&</span><span>'</span> w_variable           { Z_LVAL($$.u.constant) = <span>1</span>;  zend_do_pass_param(&$<span>2</span>, ZEND_SEND_REF, Z_LVAL($$.u.constant) TSRMLS_CC); }
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这三种op分别对应的语法是expr_without_variable、variable、'&'w_variable，简单来说就是“不含变量的表达式”、“变量”、“引用”。

zend_do_pass_param会判断，如果用户传递的是引用，但同时在php.INI中配置了形如 allow_call_time_pass_reference = Off ，则需要产生一条E_DEPRECATED错误信息，告知用户传递的时候不建议强制写成引用。

其实，还有第4种传参的opcode，即ZEND_SEND_VAR_NO_REF。我们接下来会提到。

<span>//</span><span> 函数已定义，则根据函数的定义，来决定send_by_reference是否传引用</span>
<span>if</span><span> (function_ptr) {
    </span><span>if</span><span> (ARG_MAY_BE_SENT_BY_REF(function_ptr, (zend_uint) offset)) {
        ...
    } </span><span>else</span><span> {
        </span><span>//</span><span> 要么为0，要么为ZEND_ARG_SEND_BY_REF</span>
        send_by_reference = ARG_SHOULD_BE_SENT_BY_REF(function_ptr, (zend_uint) offset) ? ZEND_ARG_SEND_BY_REF : <span>0</span><span>;
    }
}
</span><span>//</span><span> 函数为定义，先统一将send_by_reference置为0</span>
<span>else</span><span> {
    send_by_reference </span>= <span>0</span><span>;
}

</span><span>//</span><span> 如果用户传递的参数，本身就是一次函数调用，则将op改成ZEND_SEND_VAR_NO_REF</span>
<span>if</span> (op == ZEND_SEND_VAR &&<span> zend_is_function_or_method_call(param)) {
    </span><span>/*</span><span> Method call </span><span>*/</span><span>
    op </span>=<span> ZEND_SEND_VAR_NO_REF;
    send_function </span>=<span> ZEND_ARG_SEND_FUNCTION;
}
</span><span>//</span><span> 如果用户传递的参数，是一个表达式，并且结果会产生中间变量，则也将op改成ZEND_SEND_VAR_NO_REF</span>
<span>else</span> <span>if</span> (op == ZEND_SEND_VAL && (param->op_type & (IS_VAR|<span>IS_CV))) {
    op </span>=<span> ZEND_SEND_VAR_NO_REF;
}</span>
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1，send_by_reference表示根据函数的定义，参数是不是引用。ARG_MAY_BE_SENT_BY_REF和ARG_SHOULD_BE_SENT_BY_REF两个宏这里就不具体叙述了，感兴趣的朋友可以自己阅读代码。

2，op == ZEND_SEND_VAR对应的是variable，假如参数是一个函数调用，也可能会被编译成variable，但是函数调用并不存在显式定义的变量，所以不能直接编译成SEND_VAR指令，因此这里就涉及到了上文提到的第4种opcode，即ZEND_SEND_VAR_NO_REF。例如：

3，op == ZEND_SEND_VAL对应的是一个表达式，如果该表达式产生了一个变量作为结果，则也需要将op改成ZEND_SEND_VAR_NO_REF。例如：

继续来看zend_do_pass_param：

<span>//</span><span> 如果根据函数定义需要传递引用，且实际传递的参数是变量，则将op改成ZEND_SEND_REF</span>
<span>if</span> (op!=ZEND_SEND_VAR_NO_REF && send_by_reference==<span>ZEND_ARG_SEND_BY_REF) {
    </span><span>/*</span><span> change to passing by reference </span><span>*/</span>
    <span>switch</span> (param-><span>op_type) {
        </span><span>case</span><span> IS_VAR:
        </span><span>case</span><span> IS_CV:
            op </span>=<span> ZEND_SEND_REF;
            </span><span>break</span><span>;
        </span><span>default</span><span>:
            zend_error(E_COMPILE_ERROR, </span><span>"</span><span>Only variables can be passed by reference</span><span>"</span><span>);
            </span><span>break</span><span>;
    }
}

</span><span>//</span><span> 如果实际传递的参数是变量，调用zend_do_end_variable_parse处理链式调用</span>
<span>if</span> (original_op ==<span> ZEND_SEND_VAR) {
    </span><span>switch</span><span> (op) {
        </span><span>case</span><span> ZEND_SEND_VAR_NO_REF:
            zend_do_end_variable_parse(param, BP_VAR_R, </span><span>0</span><span> TSRMLS_CC);
            </span><span>break</span><span>;
        </span><span>case</span><span> ZEND_SEND_VAR:
            </span><span>if</span><span> (function_ptr) {
                zend_do_end_variable_parse(param, BP_VAR_R, </span><span>0</span><span> TSRMLS_CC);
            } </span><span>else</span><span> {
                zend_do_end_variable_parse(param, BP_VAR_FUNC_ARG, offset TSRMLS_CC);
            }
            </span><span>break</span><span>;
        </span><span>case</span><span> ZEND_SEND_REF:
            zend_do_end_variable_parse(param, BP_VAR_W, </span><span>0</span><span> TSRMLS_CC);
            </span><span>break</span><span>;
    }
}</span>
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这里注意param->op_type是传递的参数经过编译得到znode的op_type，如果不属于变量（IS_VAR、IS_CV），就直接报错了。举例来说：

<span>function</span> foo(&<span>$a</span><span>)
{
    </span><span>print</span>(<span>$a</span><span>);
}

foo(</span><span>$bar</span> == 1);  // 抛错 <span>"<span>Only variables can be passed by reference<span>"</span></span></span>
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上面 $bar == 1 表达式的编译结果，op_type为IS_TMP_VAR，可以看做一种临时的中间结果，并非IS_VAR，IS_CV，因此无法编译成功。看着逻辑有点绕，其实很好理解。因为我们传递引用，实际目的是希望能够在函数中，对这个参数的值进行修改，需要参数是可写的。然而 $bar == 1 产生的中间结果，我们无法做出修改，是只读的。

来看zend_do_pass_param的最后一段：

<span>//</span><span> 获取下一条zend op指令</span>
opline =<span> get_next_op(CG(active_op_array) TSRMLS_CC);

</span><span>//</span><span> extended_value加上不同的附加信息</span>
<span>if</span> (op ==<span> ZEND_SEND_VAR_NO_REF) {
    </span><span>if</span><span> (function_ptr) {
        opline</span>->extended_value = ZEND_ARG_COMPILE_TIME_BOUND | send_by_reference |<span> send_function;
    } </span><span>else</span><span> {
        opline</span>->extended_value =<span> send_function;
    }
} </span><span>else</span><span> {
    </span><span>if</span><span> (function_ptr) {
        opline</span>->extended_value =<span> ZEND_DO_FCALL;
    } </span><span>else</span><span> {
        opline</span>->extended_value =<span> ZEND_DO_FCALL_BY_NAME;
    }
}

</span><span>//</span><span> 设置opcode、op1、op2等</span>
opline->opcode =<span> op;
opline</span>->op1 = *<span>param;
opline</span>->op2.u.opline_num =<span> offset;
SET_UNUSED(opline</span>->op2);
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上面这段代码生成了一条SEND指令。如果我们调用函数时候传递了多个参数，则会调用多次zend_do_pass_param，最终会生成多条SEND指令。

至于指令具体是SEND_VAR，SEND_VAL，还是SEND_RE，亦或是ZEND_SEND_VAR_NO_REF，则依靠zend_do_pass_param中的判断。zend_do_pass_param中的逻辑分支比较多，一下子不能弄明白所有分支也没关系，最重要的是知道它会根据函数的定义以及实际传递的参数，产生最合适的SEND指令。

还是回到我们开始的例子，对于 foo($bar) ，则经过zend_do_pass_param之后，产生的SEND指令细节如下：

4、结束编译

结束函数调用是通过zend_do_end_function_call来完成的。根据前文所述，zend_do_begin_function_call并不产生一条实际的调用指令，但它确定了最终函数调用走的是DO_FCALL还是DO_FCALL_BY_NAME，并且据此来生成ZEND_INIT_NS_FCALL_BY_NAME或ZEND_INIT_FCALL_BY_NAME指令。

实际的调用指令是放在zend_do_end_function_call中来生成的。

具体分析下zend_do_end_function_call：

zend_op *<span>opline;

</span><span>//</span><span> 这段逻辑分支现在已经走不到了</span>
<span>if</span> (is_method && function_name && function_name->op_type ==<span> IS_UNUSED) {
    </span><span>/*</span><span> clone </span><span>*/</span>
    <span>if</span> (Z_LVAL(argument_list->u.constant) != <span>0</span><span>) {
        zend_error(E_WARNING, </span><span>"</span><span>Clone method does not require arguments</span><span>"</span><span>);
    }
    opline </span>= &CG(active_op_array)->opcodes[Z_LVAL(function_name-><span>u.constant)];
} </span><span>else</span><span> {
    opline </span>=<span> get_next_op(CG(active_op_array) TSRMLS_CC);
    
    </span><span>//</span><span> 函数，名称确定，非dynamic_fcall，函数则生成ZEND_DO_FCALL指令</span>
    <span>if</span> (!is_method && !is_dynamic_fcall && function_name->op_type==<span>IS_CONST) {
        opline</span>->opcode =<span> ZEND_DO_FCALL;
        opline</span>->op1 = *<span>function_name;
        ZVAL_LONG(</span>&opline->op2.u.constant, zend_hash_func(Z_STRVAL(function_name->u.constant), Z_STRLEN(function_name->u.constant) + <span>1</span><span>));
    }
    </span><span>//</span><span> 否则生成ZEND_DO_FCALL_BY_NAME指令</span>
    <span>else</span><span> {
        opline</span>->opcode =<span> ZEND_DO_FCALL_BY_NAME;
        SET_UNUSED(opline</span>-><span>op1);
    }
}

</span><span>//</span><span> 生成临时变量索引，函数的调用，返回的znode必然是IS_VAR</span>
opline->result.u.<span>var</span> =<span> get_temporary_variable(CG(active_op_array));
opline</span>->result.op_type =<span> IS_VAR;
</span>*result = opline-><span>result;
SET_UNUSED(opline</span>-><span>op2);

</span><span>//</span><span> 从CG(function_call_stack)弹出当前被调用的函数</span>
zend_stack_del_top(&<span>CG(function_call_stack));

</span><span>//</span><span> 传参个数</span>
opline->extended_value = Z_LVAL(argument_list->u.constant);
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其中有一段if逻辑分支已经走不到了，可以忽略。

具体考据：这段逻辑在462eff3中被添加，主要用于当调用__clone魔术方法时传参进行抛错，但在8e30d96中，已经不允许直接调用__clone方法了，在进入zend_do_end_function_call之前便会终止编译，所以实际上已经再也走不到该分支了。

直接看else部分，else生成了一条zend op指令。如果函数名确定，函数已被定义，并且不属于动态调用等，则生成的op指令为ZEND_DO_FCALL，否则生成ZEND_DO_FCALL_BY_NAME。对于ZEND_DO_FCALL指令，其操作数比较明确，为函数名，但是对于ZEND_DO_FCALL_BY_NAME来说，由于被调的函数尚未明确，所以将操作数置为UNUSED。

5、总结

用一张图总结一下函数调用大致的编译流程：

红色的方框为生成的op指令。特别是编译传参的地方，情况比较多，可能会产出4种SEND指令。

 

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