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    SubjectRe: [RFC/PATCH] Implement new PTRACE_EVENT_SYSCALL_{ENTER,EXIT}
    On 01/19, Sergio Durigan Junior wrote:
    >
    > On Friday, January 10 2014, Oleg Nesterov wrote:
    >
    > > So suppose that gdb does ptrace(PTRACE_SINGLESTEP) and the tracee
    > > executes the "syscall" insn. What it should report?
    > [...]
    > > But what should syscall-exit do? Should it still report SIGSEGV as
    > > it currently does, or should it report _SYSCALL_EXIT instead (if
    > > PTRACE_O_SYSCALL_EXIT of course), or should it report both?
    >
    > Both only if _SYSCALL_EXIT is set. Otherwise, stick to the current
    > behavior, I guess.

    OK, both. In which order? Probably _EXIT first. But this looks a bit
    strange. Suppose that the tracee reports _EXIT, then debugger does
    ptrace(PTRACE_CONT), should the tracee report SIGTRAP?

    SIGTRAP before _EXIT looks a bit strange too... Single-step trap should
    be reported after insn, but we are still in syscall.

    So perhaps _EXIT should win and do not report the step?

    > Isn't it what my current patch does, by the way?

    I forgot how this patch looks so I can be easily wrong, but iirc no.
    Note that tracehook_report_syscall_exit() doesn't even call
    ptrace_report_syscall() if step == T.

    Btw, if you send v2, please CC Michael Kerrisk <mtk.manpages@gmail.com>.

    Oleg.



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