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

[Cyrill Gorcunov]

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.