The Calling principle of member functions in C ++ and the transfer method of this pointer

The Calling principle of member functions in C ++ and the transfer method of this pointer

Write by nine days Yan Ling (jtianling) -- blog.csdn.net/vagrxie

Test source code:

1 # include
2 # include
3
4ClassCtestthispointer
5 {
6Public:
7 ctestthispointer (IntAI): MI (AI ){}
8IntAdd (IntAI)
9 {
10 MI + = AI;
11ReturnMi;
12}
13
14Private:
15IntMi;
16 };
17
18
19IntMain ()
20 {
21 ctestthispointer lotest (10 );
22
23 printf ("% d", lotest. Add (5 ));
24Return0;
25}
26

 

Disassembly:

. Text: 00401000; int _ cdecl main (INT argc, const char ** argv, const char * envp)

. Text: 00401000 _ main proc near; Code xref: _ maincrtstartup + AFP

. Text: 00401000

. Text: 00401000 this = byte PTR-4

. Text: 00401000 argc = dword ptr 8

. Text: 00401000 argv = dword ptr 0ch

. Text: 00401000 envp = dword ptr 10 h

. Text: 00401000

. Text: 00401000 push EBP; by default, we finally see an orthodox push EBP;

. Text: 00401000; MoV EBP, esp protection stack and EBP Process

. Text: 00401001 mov EBP, ESP

. Text: 00401003 push ECx

. Text: 00401004 push 0ah; the unique parameter of the constructor except this by default, 10

. Text: 00401006 Lea ECx, [EBP + This]; this pointer is passed through the ECX register.

. Text: 00401009 call ctestthispointer _ ctestthispointer

. Text: 0040100e Push 5; The add function is unique except the default this parameter, 5

. Text: 00401010 Lea ECx, [EBP + This]; this pointer

. Text: 00401013 call ctestthispointer _ add

. Text: 00401018 push eax; Add the return value of add to stack, call printf

. Text: 00401019 push offset ad; "% d"

. Text: 0040101e call _ printf

. Text: 00401023 add ESP, 8; Variable Length Parameter Function, can only be through _ cdecl call Convention Luo, by main

. Text: 00401023; function to maintain stack balance

. Text: 00401026 XOR eax, eax

. Text: 00401028 mov ESP, EBP

. Text: 0040102a pop EBP

. Text: 0040102b retn

. Text: 0040102b _ main endp

 

 

Constructor:

. Text: 00401030 ctestthispointer _ ctestthispointer proc near; Code xref: _ main + 9 p

. Text: 00401030

. Text: 00401030 var_4 = dword ptr-4

. Text: 00401030 arg_0 = dword ptr 8

. Text: 00401030

. Text: 00401030 push EBP

. Text: 00401031 mov EBP, ESP

. Text: 00401033 push ECx; save this pointer into the stack

. Text: 00401034 mov [EBP + var_4], ECx

. Text: 00401037 mov eax, [EBP + var_4]; pass the value of this to eax. By default, the optimized code is cumbersome. Next

. Text: 00401037; steps are all, in essence, nothing more than

. Text: 00401037; MoV [ECx], [EBP + arg_0] process, but because it cannot directly

. Text: 00401037; Memory mov to memory, so temporary variables are used in the middle,

. Text: 00401037; register as a temporary variable, so you must first save the register .....

. Text: 00401037; actually there are so many registers, why not? Because it is optimized by default

. Text: 0040103a mov ECx, [EBP + arg_0]

. Text: 0040103d mov [eax], ECx

. Text: 0040103f mov eax, [EBP + var_4]

. Text: 00401042 mov ESP, EBP

. Text: 00401044 pop EBP

. Text: 00401045 retn 4

. Text: 00401045 ctestthispointer _ ctestthispointer endp

 

 

Add function:

. Text: 00401050 ctestthispointer _ add proc near; Code xref: _ main + 13 p

. Text: 00401050

. Text: 00401050 var_4 = dword ptr-4

. Text: 00401050 arg_0 = dword ptr 8

. Text: 00401050

. Text: 00401050 push EBP

. Text: 00401051 mov EBP, ESP

. Text: 00401053 push ECx

. Text: 00401054 mov [EBP + var_4], ECx; the maximum fee for this temporary variable

. Text: 00401057 mov eax, [EBP + var_4]

. Text: 0040105a mov ECx, [eax]

. Text: 0040105c add ECx, [EBP + arg_0]; because the returned result is Mi, the following are honestly extracted from

. Text: 0040105c; Address to register, then retrieve the value in the form of mov re, [re]

. Text: 0040105c; BTW: I'm not used to seeing the code without optimization.

. Text: 0040105f mov edX, [EBP + var_4]

. Text: 00401062 mov [edX], ECx

. Text: 00401064 mov eax, [EBP + var_4]

. Text: 00401067 mov eax, [eax]

. Text: 00401069 mov ESP, EBP

. Text: 0040106b pop EBP

. Text: 004020.c retn 4

. Text: 00401_c ctestthispointer _ add endp

 

Write by nine days Yan Ling (jtianling) -- blog.csdn.net/vagrxie