Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32)

[Dmitry Safonov]

On 06/03/2016 12:57 PM, Cyrill Gorcunov wrote:
> On Wed, Jun 01, 2016 at 04:11:36PM +0300, Dmitry Safonov wrote:
> > As the task isn't executing at the moment of {GET,SET}REGS,
> > return regset that corresponds to code selector, rather than
> > value of TIF_IA32 flag.
> > I.e. if we ptrace i386 elf binary that has just changed it's
> > code selector to __USER_CS, than GET_REGS will return
> > full x86_64 register set.
> >
> > Note, that this will work only if application has changed it's CS.
> > If the application does 32-bit syscall with __USER_CS, ptrace
> > will still return 64-bit register set. Which might be still confusing
> > for tools that expect TS_COMPACT to be exposed [1, 2].
> >
> > So this this change should make PTRACE_GETREGSET more reliable and
> > this will be another step to drop TIF_{IA32,X32} flags.
> >
> > [1]: https://sourceforge.net/p/strace/mailman/message/30471411/
> > [2]: https://lkml.org/lkml/2012/1/18/320
> >
> > Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> > Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
>
> Looks reasonable! Still if cs has been changed to non-compat
> selector and we now return 64bit registers set, won't it
> cause problems for old tools? I suspect it should not but
> still.

Thanks! Hmm, strace works fine - I'll check gdb to be sure.
What else could be bothered by this?