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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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: > > (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: > >> On 2019/3/4 18:12, Sudeep Holla wrote: > >>> On Mon, Mar 04, 2019 at 08:25:28AM +0000, Haibo Xu (Arm Technology China) wrote: > >>>> On 2019/3/1 2:32, Sudeep Holla wrote: > >>>>> 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. > > 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel