* Steven Rostedt <rost...@goodmis.org> wrote:
> On Fri, 01 Nov 2013 11:25:37 +0000
> Masami Hiramatsu <masami.hiramatsu...@hitachi.com> wrote:
>
> > Prohibit probing on func_ptr_is_kernel_text().
> > Since the func_ptr_is_kernel_text() is called from
> > notifier_call_chain() which is called from int3 handler,
> > probing it may cause double int3 fault and kernel will
> > reboot.
> >
> > This happenes when the kernel built with CONFIG_DEBUG_NOTIFIERS=y.
> >
> > Signed-off-by: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
> > Cc: Andrew Morton <a...@linux-foundation.org>
> > Cc: "Uwe Kleine-König" <u.kleine-koe...@pengutronix.de>
> > Cc: Borislav Petkov <b...@suse.de>
> > Cc: Ingo Molnar <mi...@kernel.org>
> > ---
> > kernel/extable.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/extable.c b/kernel/extable.c
> > index 832cb28..022fb25 100644
> > --- a/kernel/extable.c
> > +++ b/kernel/extable.c
> > @@ -129,7 +129,7 @@ int kernel_text_address(unsigned long addr)
> > * pointer is part of the kernel text, we need to do some
> > * special dereferencing first.
> > */
> > -int func_ptr_is_kernel_text(void *ptr)
> > +int nokprobe func_ptr_is_kernel_text(void *ptr)
> > {
> > unsigned long addr;
> > addr = (unsigned long) dereference_function_descriptor(ptr);
> >
>
> One thing I worry about the "nokprobe" annotation, is that it moves the
> location of the function out of local. This function no exists in the
> section with its users. Same with the debug functions in the other
> patch.
Well, it's a bit like noinline, that changes the position of the function
as well. So it's not true that 'noxyz' attributes don't affect function
placement - they often don't, but some do.
The more important aspect is that 'noprobe' makes it really, really
apparent what the tag is about, at first sight.
_How_ the 'non probing' is achived is an implementational detail when
kprobes are enabled: right now it puts a function into a separate section,
but we could just a much build a list of function names and check against
it at probe insertion time.
Thanks,
Ingo
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