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    SubjectRe: [PATCH 6/6][RFC] kprobes: Allow probe on ftrace reserved text (but move it)
    (2012/04/26 11:29), Steven Rostedt wrote:
    > From: Steven Rostedt <srostedt@redhat.com>
    >
    > If a probe is placed on a ftrace nop (or ftrace_caller), simply move the
    > probe to the next instruction instead of rejecting it. This will allow
    > kprobes not to be affected by ftrace using the -mfentry gcc option which
    > will put the ftrace nop at the beginning of the function. As a very common
    > case for kprobes is to add a probe to the very beginning of a function
    > we need a way to handle the case when ftrace takes the first instruction.

    Hmm, I think you'd better introduce a flag(KPROBE_FLAG_MOVED) for
    adjustment of probed IP address. Caller or handler can fixup its IP
    or kprobes itself can do it.

    >
    > Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    > ---
    > kernel/kprobes.c | 11 ++++++++++-
    > 1 file changed, 10 insertions(+), 1 deletion(-)
    >
    > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
    > index c62b854..560d80e 100644
    > --- a/kernel/kprobes.c
    > +++ b/kernel/kprobes.c
    > @@ -1319,10 +1319,20 @@ int __kprobes register_kprobe(struct kprobe *p)
    > struct kprobe *old_p;
    > struct module *probed_mod;
    > kprobe_opcode_t *addr;
    > + unsigned long ftrace_addr;
    >
    > addr = kprobe_addr(p);
    > if (IS_ERR(addr))
    > return PTR_ERR(addr);
    > +
    > + /*
    > + * If the address is located on a ftrace nop, set the
    > + * breakpoint to the following instruction.
    > + */
    > + ftrace_addr = ftrace_location((unsigned long)addr);
    > + if (unlikely(ftrace_addr))
    > + addr = (kprobe_opcode_t *)(ftrace_addr + MCOUNT_INSN_SIZE);

    And also, you may need to use ftrace_text_reserved() here,
    or need a void ftrace_location() function for CONFIG_DYNAMIC_FTRACE=n.

    > +
    > p->addr = addr;
    >
    > ret = check_kprobe_rereg(p);
    > @@ -1333,7 +1343,6 @@ int __kprobes register_kprobe(struct kprobe *p)
    > preempt_disable();
    > if (!kernel_text_address((unsigned long) p->addr) ||
    > in_kprobes_functions((unsigned long) p->addr) ||
    > - ftrace_text_reserved(p->addr, p->addr) ||
    > jump_label_text_reserved(p->addr, p->addr)) {
    > ret = -EINVAL;
    > goto cannot_probe;

    Thanks,


    --
    Masami HIRAMATSU
    Software Platform Research Dept. Linux Technology Center
    Hitachi, Ltd., Yokohama Research Laboratory
    E-mail: masami.hiramatsu.pt@hitachi.com


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