On Feb 22, 10:13 am, jameschen <wengerm...@gmail.com> wrote:
> The question is that why ebp-12 is the "this" pointer, how to how?
> movl -12(%ebp), %eax //???????????? why ebp-12 is
> "this" pointer's address, how to know?
> movl (%eax), %eax
> addl $4, %eax
> movl (%eax), %edx
> movl $5, 4(%esp)
> movl -12(%ebp), %eax //????????????
> why ebp-12 is "this" pointer's address, how to know?
> movl %eax, (%esp)
> call *%edx ///////////
> pMyClass->test1();
>
> eg:
> #include <iostream>
> using namespace std;
>
> class MyClass
> {
> public:
> MyClass(){ data1 =1; data2 = 2;};
> ~MyClass(){};
> int data1;
> int data2;
> int data3;
> void print(int data2)
> {
> cout << "hello! data1: " << data1 << " data2: " << data2 <<
> endl;
> }
>
> virtual void test1()
> {
> data2 = 4;
> }
>
> };
>
> int main()
> {
> MyClass * pMyClass;
> pMyClass = new MyClass;
> cout << "sizeof(MyClass) = " << sizeof(MyClass) << endl;
> pMyClass->test1();
> pMyClass->print(4); // 1: ÕýÈ·µ÷ÓÃ
>
> return 0;
>
> }
>
> The ASM code of the example is:
> #################
>
> .globl main
> .type main, @function
> main:
> .LFB1401:
> leal 4(%esp), %ecx
> .LCFI19:
> andl $-16, %esp
> pushl -4(%ecx)
> .LCFI20:
> pushl %ebp
> .LCFI21:
> movl %esp, %ebp
> .LCFI22:
> pushl %ebx
> .LCFI23:
> pushl %ecx
> .LCFI24:
> subl $32, %esp
> .LCFI25:
> movl $16, (%esp)
> call _Znwj
> movl %eax, %ebx
> movl %ebx, (%esp)
> call _ZN7MyClassC1Ev
> movl %ebx, -12(%ebp)
> movl $.LC2, 4(%esp)
> movl $_ZSt4cout, (%esp)
> call
> _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES 5_PKc
> movl $16, 4(%esp)
> movl %eax, (%esp)
> call _ZNSolsEj
> movl
> $_ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamI T_T0_ES6_, 4(%esp)
> movl %eax, (%esp)
> call _ZNSolsEPFRSoS_E
> movl -12(%ebp), %eax
> movl (%eax), %eax
> addl $4, %eax
> movl (%eax), %edx
> movl $5, 4(%esp)
> movl -12(%ebp), %eax //????????????
> why ebp-12 is "this" pointer's address, how to know?
> movl %eax, (%esp)
> call *%edx ///////////
> pMyClass->test1();
> movl $4, 4(%esp)
> movl -12(%ebp), %eax
> movl %eax, (%esp)
> call _ZN7MyClass5printEi ///////pMyClass->print(4);
>
> movl $0, %eax
> addl $32, %esp
> popl %ecx
> popl %ebx
> popl %ebp
> leal -4(%ecx), %esp
> ret
> .LFE1401:
> .size main, .-main
> .local _ZSt8__ioinit
> .comm _ZSt8__ioinit,1,1
> .weak _ZTV7MyClass
> .section .gnu.linkonce.r._ZTV7MyClass,"a",@progbits
> .align 8
> .type _ZTV7MyClass, @object
> .size _ZTV7MyClass, 16
> _ZTV7MyClass:
> .long 0
> .long _ZTI7MyClass
> .long _ZN7MyClass4testEv
> .long _ZN7MyClass5test1Ei
> .weak _ZTI7MyClass
> .section .gnu.linkonce.r._ZTI7MyClass,"a",@progbits
> .align 4
> .type _ZTI7MyClass, @object
> .size _ZTI7MyClass, 8
> _ZTI7MyClass:
> .long _ZTVN10__cxxabiv117__class_type_infoE+8
> .long _ZTS7MyClass
> .weak _ZTS7MyClass
> .section .gnu.linkonce.r._ZTS7MyClass,"a",@progbits
> .type _ZTS7MyClass, @object
> .size _ZTS7MyClass, 9
> _ZTS7MyClass:
> .string "7MyClass"
> .section .eh_frame,"a",@progbits
> .

I don't know whether I describe the question clear or not£¿