Quick introduction to reverse engineering for beginners

1.15 Structures
It can be defined that C/C++ structure, with some assumptions, just a set of variables, always stored in
memory together, not necessary of the same type.
1.15.1 SYSTEMTIME example
Let’s take SYSTEMTIME 52 win32 structure describing time.
That’s how it’s defined:
typedef struct _SYSTEMTIME {
WORD wYear;
WORD wMonth;
WORD wDayOfWeek;
WORD wDay;
WORD wHour;
WORD wMinute;
WORD wSecond;
WORD wMilliseconds;
} SYSTEMTIME, *PSYSTEMTIME;
Let’s write a C function to get current time:
#include
#include
void main()
{
SYSTEMTIME t;
GetSystemTime (&t);
};
printf ("%04d-%02d-%02d %02d:%02d:%02d\n",
t.wYear, t.wMonth, t.wDay,
t.wHour, t.wMinute, t.wSecond);
return;
We got (MSVC 2010):
_t$ = -16 ; size = 16
_main PROC
push ebp
mov ebp, esp
sub esp, 16 ; 00000010H
lea eax, DWORD PTR _t$[ebp]
push eax
call DWORD PTR __imp__GetSystemTime@4
movzx ecx, WORD PTR _t$[ebp+12] ; wSecond
push ecx
movzx edx, WORD PTR _t$[ebp+10] ; wMinute
push edx
movzx eax, WORD PTR _t$[ebp+8] ; wHour
push eax
movzx ecx, WORD PTR _t$[ebp+6] ; wDay
52 MSDN: SYSTEMTIME structure
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