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

[Paul Mackerras]

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.

Paul.
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