On Tue, Mar 12, 2019 at 01:34:44AM +0000, Haibo Xu (Arm Technology China) wrote:

On 2019/3/12 2:34, Sudeep Holla wrote:

quoted

(I thought I had sent this email, last Tuesday itself, but saw this in my
draft today, something went wrong, sorry for the delay)

On Tue, Mar 05, 2019 at 02:14:47AM +0000, Haibo Xu (Arm Technology China) wrote:

quoted

On 2019/3/4 18:12, Sudeep Holla wrote:

quoted

On Mon, Mar 04, 2019 at 08:25:28AM +0000, Haibo Xu (Arm Technology China) wrote:

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On 2019/3/1 2:32, Sudeep Holla wrote:

quoted

Now that we have a new hook ptrace_syscall_enter that can be called from
syscall entry code and it handles PTRACE_SYSEMU in generic code, we
can do some cleanup using the same in syscall_trace_enter.

Further the extra logic to find single stepping PTRACE_SYSEMU_SINGLESTEP
in syscall_slow_exit_work seems unnecessary. Let's remove the same.

I think we should not change the logic here. Is so, it will double the report of syscall
when PTRACE_SYSEMU_SINGLESTEP is enabled.

I don't think that should happen, but I may be missing something.
Can you explain how ?

When PTRACE_SYSEMU_SINGLESTEP is enabled, both the _TIF_SYSCALL_EMU and
_TIF_SINGLESTEP flags are set, but ptrace only need to report(send SIGTRAP)
at the entry of a system call, no need to report at the exit of a system
call.

Sorry, but I still not get it, we have:

	step = ((flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU)) == _TIF_SINGLESTEP);

For me, this is same as:
	step = ((flags & _TIF_SINGLESTEP) == _TIF_SINGLESTEP)
	or
	if (flags & _TIF_SINGLESTEP)
		step = true;

I don't think so! As I mentioned in the last email loop, when
PTRACE_SYSEMU_SINGLESTE is enabled, both the _TIF_SYSCALL_EMU and
_TIF_SINGLESTEP flags are set, in which case the step should be "false" for
the old logic. But with the new logic, the step is "true".

Ah right, sorry I missed that.

quoted

So when PTRACE_SYSEMU_SINGLESTEP, _TIF_SYSCALL_EMU and _TIF_SINGLESTEP
are set and step evaluates to true.

So dropping _TIF_SYSCALL_EMU here should be fine. Am I still missing
something ?

--
Regards,
Sudeep

For the PTRACE_SYSEMU_SINGLESTEP request, ptrace only need to report(send
SIGTRAP) at the entry of a system call, no need to report at the exit of a
system call.That's why the old logic-{step = ((flags & (_TIF_SINGLESTEP |
_TIF_SYSCALL_EMU)) == _TIF_SINGLESTEP)} here try to filter out the special
case(PTRACE_SYSEMU_SINGLESTEP).

Understood

Another way to make sure the logic is fine, you can run some tests with
respect to both logic, and to check whether they have the same behavior.

I did run selftests after Andy Lutomirski pointed out. Nothing got flagged,
I haven't looked at the tests themselves yet, but it clearly misses this
case.

--
Regards,
Sudeep