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

From: Dmitry Safonov
Date: Fri Jun 03 2016 - 06:29:06 EST

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.


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

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