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    SubjectRe: getter PTRACE_GETSIGINFO should not modify anything [Re: [PATCH 11/11] ptrace: implement group stop notification for ptracer]
    Hello, Jan.

    On Sun, May 15, 2011 at 04:02:32PM +0200, Jan Kratochvil wrote:
    > Or there should be some other way how to query the siginfo_t state
    > fully transparently (*).
    >
    > (*) But if there exists such syscall it probably does not make sense to modify
    > anything by PTRACE_GETSIGINFO.

    If there's a syscall which doesn't affect notification state, then we
    need something which does clear it. Either way, I suppose you're
    saying we need both something which clears the notification and
    something which doesn't.

    > Imagine various LD_PRELOAD tools which try to wrap system/library calls and
    > operate with ptrace while keeping it transparent for the original debugger.
    > (I have a bunch of such libraries for testing gdb/strace/etc. written there.)
    >
    > Also complicated debuggers with internal OO hierarchy would need to just wrap
    > PTRACE_GETSIGINFO into an internal function to make it transparent for calls
    > not intending to modify the debuggee state.

    We can add a flag or new request for that but I don't know. Those are
    pretty fringe use cases and they don't even strictly require such
    feature - Even for LD_PRELOAD, it can simply keep scheduling INTERRUPT
    until the application calls the wrapped GETSIGINFO when it detects the
    stopped state has changed. It can be easily done from userland.

    Thank you.

    --
    tejun


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