linux-kernel - Re: [PATCH v4 1/2] ptrace: save the type of syscall-stop in ptrace

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Date:   Fri, 30 Nov 2018 12:29:21 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Dmitry V. Levin" <ldv@...linux.org>
Cc:     Kees Cook <keescook@...omium.org>, Jann Horn <jannh@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Elvira Khabirova <lineprinter@...linux.org>,
        Eugene Syromyatnikov <esyr@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        linux-api@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        strace-devel@...ts.strace.io
Subject: Re: [PATCH v4 1/2] ptrace: save the type of syscall-stop in
 ptrace_message

On 11/30, Dmitry V. Levin wrote:
>
> On Thu, Nov 29, 2018 at 03:47:43PM +0100, Oleg Nesterov wrote:
>
> > > so that PTRACE_GETEVENTMSG users can easily tell
> > > whether this new semantics is supported by the kernel or not.
> >
> > Yes. And how much this can help? Again, an application can trivially detect
> > if this feature implemented or not, and it should do this anyway if it wants
> > to (try to) use PTRACE_EVENTMSG_SYSCALL_ENTRY/EXIT ?
>
> How an application can easily detect whether this feature is implemented?

As I already said, it can just do ptrace(PTRACE_GET_SYSCALL_INFO, NULL) ?
If it returns -EIO then this feature is not implemented. Any other error
code (actually EINVAL or EFAULT) means it is implemented.

Oleg.