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

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Date:   Wed, 28 Nov 2018 14:49:14 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Dmitry V. Levin" <ldv@...linux.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Elvira Khabirova <lineprinter@...linux.org>,
        Eugene Syromyatnikov <esyr@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        strace-devel@...ts.strace.io
Subject: Re: [PATCH v4 1/2] ptrace: save the type of syscall-stop in
 ptrace_message

On 11/28, Dmitry V. Levin wrote:
>
> +/*
> + * These values are stored in task->ptrace_message by tracehook_report_syscall_*
> + * to describe current syscall-stop.
> + *
> + * Values for these constants are chosen so that they do not appear
> + * in task->ptrace_message by other means.
> + */
> +#define PTRACE_EVENTMSG_SYSCALL_ENTRY	0x80000000U
> +#define PTRACE_EVENTMSG_SYSCALL_EXIT	0x90000000U

Again, I do not really understand the comment... Why should we care about
"do not appear in task->ptrace_message by other means" ?

2/2 should detect ptrace_report_syscall() case correctly, so we can use any
numbers, say, 1 and 2?

If debugger does PTRACE_GETEVENTMSG it should know how to interpet the value
anyway after wait(status).

Oleg.