Re: [patch 02/11] syslets: add syslet.h include file, user API/ABI definitions

From: Paul Mackerras
Date: Sun Feb 18 2007 - 19:22:36 EST

Ingo Molnar writes:

> add include/linux/syslet.h which contains the user-space API/ABI
> declarations. Add the new header to include/linux/Kbuild as well.

> +struct syslet_uatom {
> + unsigned long flags;
> + unsigned long nr;
> + long __user *ret_ptr;
> + struct syslet_uatom __user *next;
> + unsigned long __user *arg_ptr[6];
> + /*
> + * User-space can put anything in here, kernel will not
> + * touch it:
> + */
> + void __user *private;
> +};

This structure, with its unsigned longs and pointers, is going to
create enormous headaches for 32-bit processes on 64-bit machines as
far as I can see---and on ppc64 machines, almost all processes are
32-bit, since there is no inherent speed penalty for running in 32-bit
mode, and some space savings.

Have you thought about how you will handle compatibility for 32-bit
processes? The issue will arise for x86_64 and ia64 (among others)
too, I would think.

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