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Hi,

i wrote a test function to check if pointers work, but with this function pointers do not work, only stupid values back, why ?

Here is my function:



void test(int *a)
{
*a = *a >> 1;
}

void main(void)
{
int i = 8;
test(&i);
// my function to print to screen
writeln(inttostr(i));
}

Are you sure that your inttostr() function is working properly?

Hi,
thanks for your help, yes my writeln() function works perfect. do i need a memory management for using pointers ?

bye
matze

no, but you will need pmode or v86 mode to make flat addresses work...

but if you're sure your writeln() function is working, then your pointers are working (you pass a char* to writeln(), aren't you?)

So maybe the problem is something else, like your data segment being wrong or something like that. why don't you tell us something more about your code?

p.s: do you know what is your stack doing at the moment??

gcc works fine

00000000 55 push ebp
00000001 89E5 mov ebp,esp
00000003 8B5508 mov edx,[ebp+0x8]
00000006 8B4508 mov eax,[ebp+0x8]
00000009 8B00 mov eax,[eax]
0000000B D1F8 sar eax,1
0000000D 8902 mov [edx],eax
0000000F 5D pop ebp
00000010 C3 ret
00000011 90 nop
00000012 55 push ebp
00000013 89E5 mov ebp,esp
00000015 83EC08 sub esp,byte +0x8
00000018 83E4F0 and esp,byte -0x10
0000001B B800000000 mov eax,0x0
00000020 29C4 sub esp,eax
00000022 C745FC08000000 mov dword [ebp-0x4],0x8
00000029 83EC0C sub esp,byte +0xc
0000002C 8D45FC lea eax,[ebp-0x4]
0000002F 50 push eax
00000030 E8CBFFFFFF call 0x0
00000035 83C410 add esp,byte +0x10
00000038 C9 leave
00000039 C3 ret

the only non-trivial (i mean, not a bug in writeln or inttostr) error that i can envision is that your DATA segment and your STACK segment are not aligned. I mean, you get the address of i using the %ebp register, which is itself a copy of your stack pointer %esp at some moment. both these register implicitly refer to %ss stack register. As you start manipulating it as a pointer, you (gcc) move it to a generic register (%eax and %edx) which are implicitly related to %ds ... so if %ss!=%ds, you can experience problems, especially if GDT[%ss].base != GDT[%ds].base