Thread: Pointer help

Hey guys

I am working on an OS at the moment having troubles with pointers. I have a function that only returns an int, I cannot change this, and I need to return a data structure with it. Currrently I am returning the address of the data structure;

Code:

int func() {
   ......
   ......
   return (int)&data_struct
}

The problem i have is how to get a data structure pointer to point to the value of an integer.

Code:

int addr = func();
ps_t *ps_ptr;
ps_ptr = ????

I need to get ps_ptr to point to the address that is the intergers value

for example if addr = 0x1234, how can I get the pointer to point to this memory location

any help would be greatly appricated

- malkav

>> I have a function that only returns an int, I cannot change this,
> Why not? you're in control of everything.
> Sure you could smash the type system away and assume that pointers and > > > integers are the same size, but that's hardly the way to go.
> How are you going to ensure for example that data_struct is always a ps_t ?
I cannot change what the function returns because they are system call. If I changed it, I would have to change all system calls and all processes that depend on the system calls. And no I did not didn't program this, it was programmed by some one else.

>> return (int)&data_struct
> What's the betting this is a local variable?
It is not, the OS uses a flat memory space at the moment and processes can access any memory location

>> ps_ptr = ????
> You've already polluted your code with a cast, just add another one.
Im not sure what you mean, ps_ptr = (ps_t *)addr will cast the value of addr into the structure. I need to point to the memory address of the value.

Well every one has to start some where, how else am i going to learn?

Like i said if i could change the return type to a void * then I already would have but there is too much code that depends on it. All the systems calls have single entry point into the kernel so are contained in a wrapper function. This wrapper returns an int. There is no way I can feasibly change it without days and possible weeks of extra work

I can do it in assembly like this;

mov $addr, %eax
then access the structure with (%eax), 4(%eax) etc... but i would have like to find the solution in C

> It seems to me you know squat about C, never mind anything else.
I wouldn't say I know squat, but I can only dream of the day I can proclaim myself "god of the C" and sit on forums all day flaming people.

> Well the longer you leave it, the worse it will get.
It is just not possible, there are external applications that are not under my control that depend on the syscall interface

> What happens when int is no longer large enough to return your answer?
It will always run on a 32bit architecture so should be adequate.