Re: [PATCH] x86_64: handle iret faults better

[Roland McGrath <roland@redhat.com>]

> Why don't you just do
> 
> 	pushl $0
> 	pushl $do_iret_error
> 	jmp error_code

I quote from the comment in the code:

								   We want
 * to turn it into a signal.  To make that signal's info exactly match what
 * this same kind of fault in a user instruction would show, the fixup
 * needs to know the trapno and error code.  But those are lost when we get
 * back to the fixup entrypoint.  

The error code is not always 0, it might be a bad segment value.  I think
the kernel ought to give accurate information about the fault consistently
no matter where it occurs, so I did not want to pretend the error code is 0.

I certainly think it would be cleaner if the fixup code could access the
fault information directly.  However, it's arguably not so clean to have a
do_iret_error function that replicates the work of do_trap and
do_general_protection.  The iret case is really not so much a special case
for what to do, but a special case for how you determine whether the
vanilla user-mode thing is done or the vanilla kernel-mode thing is done.


Thanks,
Roland