On Tue, Feb 13, 2007 at 03:20:42PM +0100, Ingo Molnar wrote:
> +Arguments to the system call are implemented via pointers to arguments.
> +This not only increases the flexibility of syslet atoms (multiple syslets
> +can share the same variable for example), but is also an optimization:
> +copy_uatom() will only fetch syscall parameters up until the point it
> +meets the first NULL pointer. 50% of all syscalls have 2 or less
> +parameters (and 90% of all syscalls have 4 or less parameters).
> +
> + [ Note: since the argument array is at the end of the atom, and the
> + kernel will not touch any argument beyond the final NULL one, atoms
> + might be packed more tightly. (the only special case exception to
> + this rule would be SKIP_TO_NEXT_ON_STOP atoms, where the kernel will
> + jump a full syslet_uatom number of bytes.) ]
What if you need to increase the number of arguments passed to a system
call later? That would be an API change since the size of syslet_uatom
would change?
Also, what if you have an ABI such that:
sys_foo(int fd, long long a)
where:
arg[0] <= fd
arg[1] <= unused
arg[2] <= low 32-bits a
arg[3] <= high 32-bits a
it seems you need to point arg[1] to some valid but dummy variable.
How do you propose syslet users know about these kinds of ABI issues
(including the endian-ness of 64-bit arguments) ?
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of:
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