[Linux-ia64] Re: is casting of function descriptor assignments for ia64 ONLY a good idea?

Grant Grundler
2002-01-03T17:35:51Z

Piet/Pete Delaney wrote:
> SUMMARY:
>
> Keith Owens just pointed out that ia64 function descriptor assignments
> MUST be cast:
>
> pointer = ((unsigned long *)(&my_printf))[0])
>
> howerver it appears that other platforms MUST NOT be cast.

I'm pretty sure parisc64 (ELF) does something similar.

We had issues with 32<->64 bit syscall wrappers where a 32-bit user space
structure passed to the kernel contained a function pointer. I thought it
was in either ioctl32.c or sys_wrapper32.c:
http://cvs.parisc-linux.org/linux/arch/parisc/kernel/

but couldn't find the exact code.
IIRC, a function ptr has 4 elements and the 3rd contains the addr
to the actual code.

> I've used pointers to functions a lot in the past and I don't recall
> ever haveing a problem like this.

IIRC, the compiler/linker deal with this transperently.
It's only done with function pointers (and not other pointer types).
I only remember seeing this as an issue in 32-64 syscall wrapper conversion.

grant