Re: [PATCH][v4] uprobes/x86: emulate push insns for uprobe on x86

[Yonghong Song]

On 11/20/17 8:41 AM, Oleg Nesterov wrote:
> On 11/17, Yonghong Song wrote:
> > On 11/17/17 9:25 AM, Oleg Nesterov wrote:
> > > On 11/15, Yonghong Song wrote:
> > > > v3 -> v4:
> > > >    . Revert most of v3 change as 32bit emulation is not really working
> > > >      on x86_64 platform as among other issues, function emulate_push_stack()
> > > >      needs to account for 32bit app on 64bit platform.
> > > >      A separate effort is ongoing to address this issue.
> > >
> > > Reviewed-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> > >
> > >
> > >
> > > Please test your patch with the fix below, in this particular case the
> > > TIF_IA32 check should be fine. Although this is not what we really want,
> > > we should probably use user_64bit_mode(regs) which checks ->cs. But this
> > > needs more changes and doesn't solve other problems (get_unmapped_area)
> > > so I still can't decide what should we do right now...
> >
> > I tested the below change with my patch. On x86_64, both 64bit and 32bit
> > program can be uprobe emulated properly.
>
> Good, so your patch is fine.

Thanks!

> > On x86_32, however, there is a
> > compilation error like below:
>
> Yes, yes, when I said "in this particular case" I meant x86_64 system only.
>
> Sorry for confusion, I asked you to test this additional change just to
> ensure that we didn't miss something and your patch has no problems with
> 32bit tasks on 64bit system, except those we need to fix anyway.

Understood. I actually tried a little to see whether I could have a 
simple way to fix 32bit compilation error without using ugly "#ifdef 
CONFIG_X86_64". Maybe is_64bit_mm is a good choice. But we could defer 
this until you have a comprehensive fix for 32bit app uprobe on 64bit 
systems as there are multiple issues for this.

> Oleg.