Foreword: This article is from a question of a question in the 9CBS Forum. It is now organized to help friends with the same needs.
Friends who have been dynamically loaded with DLL should be clearly getprocaddress this API, which is to obtain this function from the DLL module through a function name, and then convert it into a corresponding function pointer for us to call. This is a typical example of calling a function through a function name. Below we simulate this function, the main idea is to create a function mapping table.
#include
Using
Namespace
STD;
/ / Define function entry structure
Typedef
Void (* fun_ptr)
Void);
Struct fun_ENTRY
{
Const
Char * fun_name;
// Function Name
Fun_PTR FUN_PTR;
// Function pointer, actually the data type here can also be integer
}
// Define two different prototypes
Void foo1 () {cout <<
"foo1" << Endl;
INT foo2
INT i) {cout <<
"foo2:" << i << endl;
Return 0;}
// Define function mapping table
FUN_ENTRY FUN_ENTRY_TABLE [] =
{
{
"foo1", (fun_ptr) foo1},
{
"foo2", (fun_ptr) foo2}
}
// Simulation GetProcaddress
Fun_ptr Get_Proc_Address (Const)
Char * fun_name)
{
FOR
INT i = 0; i <
SIZEOF (fun_entry_table) /
SIZEOF (fun_entry_table [0]); i )
{
IF (strcmp (fun_name, fun_entry_table [i] .fun_name) == 0)
RETURN FUN_ENTRY_TABLE [I] .fun_ptr;
}
Return NULL;
}
int main ()
{
Typedef
Void (* foo1_ptr)
Void);
Typedef
INT (* foo2_ptr)
Int);
FOO1_PTR PFOO1 = (Foo1_Ptr) Get_Proc_Address
"foo1");
// Get the function entry address and convert to a function pointer
IF (PFOO1) PFOO1 ();
// Vire to call functions
Foo2_ptr pfoO2 = (foo2_ptr) get_proc_address (
"foo2");
IF (PFOO2) PFOO2 (100);
SYSTEM
"PAUSE");
Return 0;
}
Is it very simple, how can get procaddress implement? This is still not clear, but we know that there are function symbol information in the DLL, which can easily locate the entrance address of a function. If there is a function name in the binary code of the ordinary program, then it is not very cool! But this is exposed to the internal implementation of the program, which can greatly facilitate hackers, :).
Today is 9.18, don't forget the national humiliation, revitalize China!
(Freefalcon at 2004.09.18)
