linux-kernel - Re: [PATCH 3/6] x86: clean up _TIF_SYSCALL_EMU handling using ptrace_syscall

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Date:   Tue, 5 Mar 2019 02:14:47 +0000
From:   "Haibo Xu (Arm Technology China)" <Haibo.Xu@....com>
To:     Sudeep Holla <Sudeep.Holla@....com>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Will Deacon <Will.Deacon@....com>,
        Oleg Nesterov <oleg@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Richard Weinberger <richard@....at>,
        "jdike@...toit.com" <jdike@...toit.com>,
        Steve Capper <Steve.Capper@....com>,
        "Bin Lu (Arm Technology China)" <Bin.Lu@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 3/6] x86: clean up _TIF_SYSCALL_EMU handling using
 ptrace_syscall_enter hook

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 ?
>
> --
> Regards,
> Sudeep
>

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.

Regards,
Haibo
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