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SubjectRe: [PATCH 16/17] arm: asm/syscall.h (unfinished)
On Fri, Apr 24, 2009 at 05:15:03PM -0700, Roland McGrath wrote:
> The syscall_get_nr() function here is not really right. I don't
> know enough about ARM to finish it correctly. It needs to figure
> out if the blocked user task is really in the kernel for a system
> call and return -1 if not.

That bit is rather hard - we maintain no global state as to whether a
task is in a syscall or not. We also do not maintain a global view
of which syscall number is being executed. The kernel just hasn't
required either of these things before.

> I also did not try to handle all the different ABI variants, which I
> don't really understand.

There are two places that the syscall number comes from: EABI and thumb
both use R7. OABI puts the value in the instruction itself.

In short, I don't know what to do about this either. I don't think
there's a quick and simple answer.

Your implementation of syscall_get_arguments() looks wrong - for OABI
it makes sense because there is no padding in the allocation of registers.
However, for EABI, there is padding, so 64-bit values always come in
using an even+odd register number. Short of maintaining some sort of
table describing the argument placements for every kernel syscall (eww)
I'm not sure how this could be fixed.

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of:


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