Function calling convention

Catalog

One 、 The role of function calling conventions

Two 、stdcall

3、 ... and 、cdecal

Four 、fastcall

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One 、 The role of function calling conventions

The function call is realized by the storage structure of stack , But there are several problems involved , Like the following function ：

int add(int a, int b) {
    return a + b;
}
int main {
    add(1, 2);
    return;
}

（1） How to ensure the stack order of parameters ？ First a after b, Or first? b after a？

（2） After the function call , Who is responsible for restoring the top pointer ？

Function calling convention is to solve these problems , And different function call conventions will produce different function name modifiers , Different language conventions are different , There are mainly ：stdcall、cdecal、fastcalll.

Two 、stdcall

stdcall yes C++ Standard call mode of , The calling convention is ：

1） Parameters are pushed right to left , Corresponding to the above example, first b after a;

2） The callee is responsible for restoring the stack top pointer

Because the variable parameters are similar printf(), The number of parameters is only known during execution , The callee does not know how many parameters are passed in , therefore stdcall The implementation of variable parameters is not supported .

Use stdcall The function name of the calling convention will be decorated with an underscore prefix plus @ And the number of bytes of the parameter , The above example is [email protected]

3、 ... and 、cdecal

yes C Language default calling convention ;

1） Parameters are pushed onto the stack from right to left ;

2） The caller is responsible for restoring the stack top pointer

And stdcall The only difference is who is responsible for restoring the top pointer and the name of the compiled function ,cdecal The function name compiled by the method has only one in front “_” Prefix .

Four 、fastcall

1） Parameters are pushed onto the stack from right to left ;

2） Call the function to recover the stack top pointer ;

3） Parameters are preferentially passed by registers .

fastcall The reason why it is fast is that parameters will be passed in priority using registers , The compiled function name format is ：@[email protected]