Re: [RFC][PATCH 0/3] ftrace: Add dynamically allocated trampolines

From: Jiri Kosina
Date: Fri Jul 11 2014 - 09:24:37 EST

On Fri, 11 Jul 2014, Masami Hiramatsu wrote:

> >> I did some testing with kpatch and I found one minor issue. The dynamically
> >> allocated trampoline seems to confuse dump_stack() somewhat.
> >>
> >> I added a dump_stack() call in my ftrace_ops callback function
> >> (kpatch_ftrace_handler) which had a filter on meminfo_proc_show().
> >
> > Interesting. Are you using dwarf2 unwinder for stack dumping by any
> > chance? It seems to get things right here. Will look into it more
> > tomorrow.
> Hmm, can dwarf2 unwinder work on the trampoline method? Since the
> trampoline just a copy of instructions which will not have CFI(which is
> stored in dwarf section), I guess it may not work... Frame pointer (push
> bp and save sp to bp on the entry) can work anyway.

That was exactly my idea and that's why I asked, thanks for confirming.

I am afraid we'll have to declare dynamic trampolines incompatible with
drawf2 stack dumping.

Jiri Kosina
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at