2020-09-04: do you understand the function call convention?

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Fogo's answer 2020-09-04：
Primary answer ：

stdcall and cdecl Both parameters are passed from right to left .
The difference is stdcall In the called function (Callee) Return to the former , By the called function (Callee) Adjust the stack .cdecl In the called function (Callee) After the return , By the caller (Caller) Adjust the stack , Every function that calls it contains the code to empty the stack , So the size of the resulting executable is larger than that of the call _stdcall The size of the function .

Intermediate answer ：

1.__stdcall
In the called function (Callee) Return to the former , By the called function (Callee) Adjust the stack
Parameters are pushed right to left onto the stack .
The function name is automatically underlined before it , Followed by one @ Symbol , It's followed by the size of the parameter .

2.__cdecl
In the called function (Callee) After the return , By the caller (Caller) Adjust the stack .
Function arguments are stacked on the program stack from right to left .
Function results are stored in registers EAX/AX/AL in
Floating point results are stored in registers ST0 in
The compiled function name is prefixed with an underline character
The caller is responsible for ejecting arguments from the thread stack （ Clear the stack ）
8 Bit or 16 The actual parameters of plastic surgery are improved to 32 Better than .
Registers affected by function calls （volatile registers）：EAX, ECX, EDX, ST0 - ST7, ES, GS
Registers that are not affected by function calls ： EBX, EBP, ESP, EDI, ESI, CS, DS
RET Instruction returns from the callee of the function to the caller （ It's essentially reading registers EBP The return address of the function stored at the thread stack and loaded into IP register ）

3.__fastcall
__fastcall The main feature of call is fast , Because it transfers parameters through registers .
actually __fastcall use ECX and EDX Send the first two DWORD Or smaller , The remaining parameters are still pushed from right to left , The called function cleans up the memory stack of the transfer parameters before returning .
__fastcall The calling convention adds a “@” Symbol , There's also a “@” Bytes of symbols and their parameters , The format is @function @number , Such as double multi(double a, double b) The modifier name of is @[email protected]
__fastcall and __stdcall Much like the , The only difference is that the first two parameters are passed through registers . Note that the two parameters passed through the register are left to right , That is to say 1 Parameters in ECX, The first 2 Advance in EDX, Other parameters are right to left push , Return still pass EAX.

fastcall Call Convention and stdcall similar , It means that the ：

1. The first and second of the function DWORD Parameters （ Or smaller ） adopt ecx and edx Pass on , Other parameters are stacked in order from right to left ;
2. The called function cleans the stack ;
3. The rules for modifying function names are the same as stdcall.

Fast Calling Convention, Quick call Convention . Solve efficiency problems by using registers . characteristic ：
Function parameters are passed through registers , The two leftmost of the functions DWORD（ The register size is double word ） Or smaller parameters , Pass... By register . The rest is passed from the right to the left stack . Function name adaptation ：“@ Function name @ Function parameter byte size decimal ”. Return in the same way __stdcall.

4.__thiscall
thiscall Is the only functional modifier that can't be specified , because thiscall Not a keyword . It is C++ The default calling convention of class member function . Because the member function call has another this The pointer , Therefore, special treatment is necessary ,thiscall signify ：

1. Parameters are pushed from right to left ;
2. If the number of parameters is determined ,this Pointer through ecx Pass to callee ; If the number of parameters is uncertain ,this The pointer is pushed onto the stack after all parameters are pushed onto the stack ;
3. Variable number of parameters , The caller cleans the stack , Otherwise, the function cleans the stack itself .

Mainly used to solve this Pointer problem , Use registers to pass this The pointer . Return in the same way __stdcall.

5.__nakedcall
This is a very rare calling convention , General programmers recommend not to use . The compiler does not add initialization and cleanup code to this function , What's more special , Out-of-service return Return return value , Only insert assembly can return the result .

6.__pascal
be based on Pascal Call convention of language , Parameters are put on the stack from left to right ( And cdecl contrary ). The callee is responsible for cleaning the stack before returning . This calling convention is common in the following 16-bit The compiler for the platform ：OS/2 1.x, Microsoft Windows 3.x, as well as Borland Delphi edition 1.x.

7.__vectorcall
The purpose is to optimize floating-point vector operations ,intel There are many floating-point vector registers in the processor , The traditional calling convention （stdcall cdecl fastcall thiscall） All through general registers （ecx edx /rcx rdx r8 r9） And stack for parameter passing , So when you call it , Floating point parameters need to be taken from the stack .

It is required to pass parameters in registers as much as possible . The function name is adapted to ”@@ Function name @ Parameter byte number decimal ”. This is Microsoft's own standard .

8.syscall
And cdecl similar , Arguments are pushed right to left onto the stack .EAX, ECX and EDX Values are not preserved . The size of the parameter list is placed in AL In the register (?). syscall yes 32 position OS/2 API Standards for .

9.optlink
Parameters are also pushed onto the stack from right to left . The three character arguments starting from the far left are placed in EAX, EDX and ECX in , Up to four floating-point arguments are passed in ST(0) To ST(3) in ---- Although the space of these four parameters will be reserved on the stack of parameter list . The return value of the function is in EAX or ST(0) in . The Reserved registers are EBP, EBX, ESI and EDI. optlink stay IBM VisualAge It is used in compilers .

10.__clrcall
__clrcall yes C++ .Net Inside .

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