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    SubjectRe: [PATCH] uprobes: don't enable/disable signle step if the user did it
    On 07/31, Srikar Dronamraju wrote:
    >
    > * Oleg Nesterov <oleg@redhat.com> [2012-07-30 16:16:38]:
    >
    > > So I think we need arch_uprobe_*able_step(struct uprobe_task *utask).
    > > Ignoring all problems except the one this patch tries to fix, x86
    > > can simply do:
    > >
    > > arch_uprobe_enble_step(utask, struct arch_uprobe *auprobe)
    > > {
    > > utask->clear_tf =
    > > !(regs->flags & X86_EFLAGS_TF) &&
    > > (auprobe->insn != "popf");
    > > regs->flags |= X86_EFLAGS_TF;
    > > }
    > >
    > > arch_uprobe_disable_step(utask)
    > > {
    > > if (utask->clear_tf)
    > > regs->flags &= ~X86_EFLAGS_TF;
    > > }
    > >
    >
    > We were using something similar to this approach. [though we were still
    > using TIF_SINGLESTEP flag].

    (and afaics the code was wrong)

    > However this was all changed based on
    > feedback from Roland and Peter.
    >
    > Here is the pointer to the discussion.
    >
    > https://lkml.org/lkml/2011/1/27/283

    Looking at this discussion now, I am not sure that Roland was against
    the per-arch uprobe_enable_step() implementation.

    And when I read you message I do not understand your opinion ;)

    And just in case, the pseudo code above is only for illustration,
    note also "Ignoring all problems except the one".

    In any case I agree, this needs more discussion. Personally I think
    it doesn't make sense to try to teach user_enable_single_step() to
    work correctly with ptrace and uprobes at the same time, I can be
    wrong of-course.

    Oleg.



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