[CRIU] [PATCH] compel: Do not loose sign of result in compat syscall

[Cyrill Gorcunov]

On Tue, Oct 31, 2017 at 12:43:04PM +0000, Dmitry Safonov wrote:
> 2017-10-31 12:33 GMT+00:00 Cyrill Gorcunov <gorcunov at gmail.com>:
> > On Tue, Oct 31, 2017 at 12:08:11PM +0000, Dmitry Safonov wrote:
> >> >
> >> > Not exactly. We could generate a mask from it but I think it's not that required,
> >> > at least by now.
> >>
> >> Wait, I kind of don't get it:
> >> How map can be > 4 bytes if you get it from (user_regs_struct32::ax), which is
> >> 4 bytes (u32) for compat tasks?
> >> We may insert BUG_ON(map & 0xffffffff00000000) or something.
> >
> > Because we convert uint -> int -> long, and the sing of int get
> > propagated to upper bits. The map can't be more than 4 bytes but
> > we use signed long to keep the result.
> 
> Ok, I see, the sign extension.
> It's not a very lovely solution but should work.

We didn't merge any into vanilla criu yet, so if you have a better
idea -- you are more than welcome!