From: Andi Kleen <andi@firstfloor.org>
Date: Sat, 22 Dec 2007 01:42:02 +0100

quoted text
> David Miller <davem@davemloft.net> writes:
> 
> > Only on x86 platforms.  Sparc, IA64, MIPS, powerpc, etc. all get this
> > case right.
> 
> Do they for 32bit kernels or for 64bit userland? 

Both.  This is not a compat issue.

quoted text
> > Yes it's another unfortunate side effect of how error status is
> > indicated for x86 system calls.
> 
> Maybe I'm dense, but doesn't all the kernel code pass it the
> same way as the x86 syscall code? For your proposal you
> would need a separate error bit coming out of the sys_* to
> handle this case. Basically rewrite all code that ever returns
> errors in the kernel. Or do I miss something? 

I'm suggesting that you set the condition codes based upon whether
there is an error or not.  That is the critical thing x86 doesn't do
that all the other platforms do.

x86 relies on interpretation of purely the integer returned from the
system call to userspace, and that means a certain chunk of the return
value space can never represent valid values.

If you use the condition codes to signal "the return value is an
error" you don't have these problems.
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