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    Subject[PATCH 6/6][RFC] kprobes: Allow probe on ftrace reserved text (but move it)
    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.

    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);
    +
    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;
    --
    1.7.9.5

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