Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)

H. Peter Anvin
2011-08-23T23:05:01Z

On 08/23/2011 02:20 PM, Linus Torvalds wrote:
> On Tue, Aug 23, 2011 at 2:08 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>>
>> Again, can we steal one of the padding fields to use for that state
>> variable? We have two 16-bit padding fields; one for cs and one for ss.
>
> We can steal them for passing the information to the user, but no, I
> don't think we can use them to then take the information *from* the
> user.
>
> Somebody may well be setting up a 'pt_regs' structure on his own, and
> simply not fill in the padding, resulting in random data in those
> fields.
>

That would be fine, I'd think... just gives the user space application
enough information to know how it would have to reshuffle the registers
if it needs to.

-hpa