Re: RFC: is_compat_task (Was: Re: input compat stuff)

[Andi Kleen <ak@suse.de>]

On Wed, Jun 29, 2005 at 02:09:44AM +1000, Stephen Rothwell wrote:
> On Tue, 28 Jun 2005 11:17:04 +0200 Andi Kleen <ak@suse.de> wrote:
> >
> > On Tue, Jun 28, 2005 at 06:14:53PM +1000, Stephen Rothwell wrote:
> > > On Tue, 28 Jun 2005 09:27:10 +0200 Christoph Hellwig <hch@lst.de> wrote:
> > > >
> > > > besides this beeing butt ugly didn't we have a rule about never checking
> > > > task flags whether we're a compat process?  And if we're going to allow
> > > > it it should be done properly.
> > > 
> > > So, I have been thinking about this patch for a while (wondering how badly
> > > flamed I would get when I posted it :-)).  What do you all think?  Is this
> > > a reasonable thing to do?
> > 
> > No, it's not because it makes it impossible to have 64bit processes
> > that run with 32bit ABI (not implemented right now but we don't
> > want to break that).
> 
> Why does this make it impossible?  All I am defining is *arch specific*
> macros that tell us if the kernel was entered through a compat syscall. If

No, you're defining an arch specific macro to tell you that
the current process was loaded from a 32bit executable.
It does not tell you anything how the kernel was entered.

Subtle but important difference.

> 
> > Please don't do this. It is absolutely the wrong thing to do.
> 
> Then please tell us what the right thing to do is.

The right thing to do is what all the other non broken compat
functions do - figure out from the original system call entry
point if you're in compat context or not.

This typically requires a special path.

-Andi