Messages in this thread | | | Date | Thu, 9 Feb 2017 19:09:12 +0000 | From | Abel Vesa <> | Subject | Re: [PATCHv3] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS |
| |
On Thu, Feb 09, 2017 at 07:01:10PM +0000, Abel Vesa wrote: > On Thu, Feb 09, 2017 at 01:14:52PM -0500, Steven Rostedt wrote: > > > > [ sending again with Masami Cc'd ] > > > > On Thu, 9 Feb 2017 13:14:14 -0500 > > Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > On Thu, 9 Feb 2017 18:06:44 +0000 > > > Russell King - ARM Linux <linux@armlinux.org.uk> wrote: > > > > > > > On Thu, Feb 09, 2017 at 12:13:22PM -0500, Steven Rostedt wrote: > > > > > Then came along live kernel patching, which I believe this series is > > > > > trying to support. What is needed by pt_regs is a way to "hijack" the > > > > > function being called to instead call the patched function. That is, > > > > > ftrace is not being used for tracing, but in reality, being used to > > > > > modify the running kernel. It is being used to change what function > > > > > gets called. ftrace is just a hook for that mechanism. > > > > > > > > So, would I be correct to assume that the only parts of pt_regs that > > > > would be touched are those which contain arguments to the function, > > > > and the register which would contain the return value? > > > > > > > > > > For live kernel patching, perhaps. > > > > > > But for kprobes, I think they can touch anything. Matters what the > > > creater of the kprobe wanted to do. > > > > Thing is, by saving all of them is the easiest way to ensure that the > whole context is the same when the replacing function gets called, as > I said before. > > We can't be sure that while __ftrace_ops_list_func is executing, any of > the regs will have the value they had when the function-to-be-replaced > was called. That's the reason I say we need to save them all. Scratch that, I'm wrong, the reason is stupid. The context gets restored anyway after __ftrace_ops_list_func is done. > > > -- Steve > >
| |