I'm using IDA Pro to disassemble the following C code: However looking at the disassembly below it seems to me incomplete. The data is never initialized (as per C code) even though it does appear to be loaded into the stack however the procedure (nullsub_1) that is located at 00401040 makes no use of the data ? Am I making a correct assessment or am I missing something ??? I have used Visual C++ 6/2005 to compile the C code.
#include <stdio.h>
#include <windows.h>
struct a
{
char s[10];
BYTE b;
int i;
};
a al;
void init(a);
void main()
{
init(al);
};
void init(a c)
{
for(int j = 0; j < 10; j++) c.s[j] = 'A';
c.b = 10;
c.i = 10000;
};
.text:00401000 ; int __cdecl main(int argc,const char **argv,const char *envp)
.text:00401000 _main proc near ; CODE XREF: start+AFp
.text:00401000
.text:00401000 argc = dword ptr 4
.text:00401000 argv = dword ptr 8
.text:00401000 envp = dword ptr 0Ch
.text:00401000
.text:00401000 mov ecx, dword_4084C0
.text:00401006 mov edx, dword_4084C4
.text:0040100C sub esp, 10h
.text:0040100F mov eax, esp
.text:00401011 mov [eax], ecx
.text:00401013 mov ecx, dword_4084C8
.text:00401019 mov [eax+4], edx
.text:0040101C mov edx, dword_4084CC
.text:00401022 mov [eax+8], ecx
.text:00401025 mov [eax+0Ch], edx
.text:00401028 call nullsub_1
.text:0040102D add esp, 10h
.text:00401030 retn
.text:00401030 _main endp
.text:00401030
.text:00401030 ;
.text:00401031 align 10h
.text:00401040
.text:00401040
.text:00401040
.text:00401040 nullsub_1 proc near ; CODE XREF: _main+28p
.text:00401040 retn
.text:00401040 nullsub_1 endp
Your source code has no side effects other than just writing to memory. The compiler eliminates those writes as useless.
You may have better luck if you compile it in Debug mode (instead of Release) or turn off some compiler optimizations.
Alternatively, accesses to variables defined as volatile will be preserved, so you can add volatile in your code.